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good evening welcome to the lunar and

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planetary institute as we continue our

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2013-2014 cosmic exploration speaker

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series uh the universe is out to get us

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in what we can or can't do about it our

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first

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presentation a few months ago was about

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the sun and what it throws at us

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which is bad usually and tonight we're

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going to be talking about asteroid

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impacts on the earth and it's a little

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bit uh fortuitous we actually were

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supposed to have this talk a few weeks

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ago and we rescheduled it to this week

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and it happened to coincide with a

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really cool event that uh dr mackel will

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tell you a little bit about here in a

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bit

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uh our next presentation will be march

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6th so we're taking a few months off so

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don't forget march 6. we have flyers out

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front for it the topic will be on

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gamma-ray bursts and supernova

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and also note our april presentation was

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originally the 17th we have also

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rescheduled that for april 24th

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so please note that

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we have our email list sign up sheet out

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front as always we also have some

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goodies on the table by the on the other

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side of the front door for you to pick

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up and take home

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teachers if you're with us with your

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professional development certificates at

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the receptionist desk pick up one of

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those before you leave and last time we

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asked you to fill an evaluation so if

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you could do that again even if you did

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do it a few months ago we'll be walking

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around with an ipad again if you want to

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do it that way we have paper surveys at

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the front door and we can also give you

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a slip with a url you can take home

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without if you want to

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when you when you get home

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and don't forget our reception

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afterwards of course

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and we have a shuttle i don't know if

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anybody here need to take the shuttle

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tonight but if you did they will leave

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here for the last time to go back to the

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church at 9 30. so make sure you're on

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the 9 30 bus

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so to speak

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if you need to

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all right so to tell us more about

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tonight's speaker i'm going to ask dr

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stephen mackwell to come up and do that

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dr mackwell is the director of the lunar

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thanks andy um

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welcome it's a great pleasure to have

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you here tonight

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as andy mentioned we have uh an event

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going on uh in the building at the

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moment um it's a nasa sponsored event um

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that's here was

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from started up last night it's gone

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going today and then tomorrow morning

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it's a continuation of a meeting that we

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started

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the 30th of september an auspicious day

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we started the meeting was supposed to

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go for three days it lasted for one then

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the government shutdown

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so 51 days later we started it up again

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um and um

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as andy mentioned it's kind of a

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something of a coincidence because the

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meeting is all about nasa's plans for an

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asteroid retrieval mission and so

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it's rather interesting and um

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coincidence in a way that uh and that we

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have david king scheduled to speak

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tonight on the recent chugibinsk um

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airburst in russia so

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uh it's my great pleasure to introduce

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david kring tonight david is a senior

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staff scientist at the lunar and

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planetary institute here

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one of my scientists great pleasure to

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have him around

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david did his bachelor's degree at

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indiana university

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in geology

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moved from there uh did his phd at

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harvard university

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from there oh i should mention that

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while he was doing his undergraduate

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work he was an intern here at the lpi in

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1983 so he has a long history with the

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lpi

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after he finished his phd he moved to

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the

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division of

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the lunar and planetary laboratory at

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the university of arizona and the

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department of geosciences at the

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university of arizona

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where he kind of moved up in the wrongs

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to become an associate professor

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and managed

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the

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lunar planetary institute first as a

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visiting scientist and then said he

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liked us so much he stayed um and is now

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one of my senior scientists david um has

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a number of accomplishments um i could

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go through his long long list of things

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that he's done and the the commitments

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that he's made to the planetary science

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community over the years um

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but i'll just mention the awards that

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he's received he's a fellow of the

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meteoritical society a fellow of the

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geological society of america um he just

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recently received the rongrelio

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award for distinguished services that is

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given out by the geological society of

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america

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and he has a an asteroid named after

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himself

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which is quite fortuitous um david is an

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expert on on impact processes and most

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much of the time he's been here he's

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been the director of the

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center for uh lunar science and

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exploration um here uh running a group

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of people working on on impact processes

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on the moon

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um

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but his background is much broader than

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that and we're going to hear some of his

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breath tonight when he's talking about

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asteroids of course that's the other

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part of the impact process not just

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what's hit but what's hitting it

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so without further ado i will pass the

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microphone to david who's going to talk

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about the 2013 chalyburn scare burst and

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the hazards of near-earth asteroid

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thank you very much uh let's go ahead

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and dig in

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i want to start with the news friday

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february 15

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2013. for those of us in north america

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you may have been waking up turning on

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the radio and getting the first first

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news it may have been over lunch when

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colleagues around the coffee pot said

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did you hear where it may have been in

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the evening when you got home and you

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turned on the evening news but the

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headline was small asteroid penetrates

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earth atmosphere or with some news

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organizations a little bit more dramatic

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terminology

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when this impact occurred

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the sun was illuminating the eastern

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pacific ocean

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dawn was beginning to sweep westward

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across asia as this asteroid made its

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way

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towards the earth

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and impacted uh in the early morning

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hours

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coming from the direction of the sun so

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it was completely unseen

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unexpected and um as you will see in a

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few minutes it startled a great number

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of people in russia

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okay to illustrate

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this trajectory towards the earth i'm

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going to use a video that some of my

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colleagues in the czech republic and the

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university of western ontario produced

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so imagine yourself as a space cowboy

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sitting on top of this asteroid and

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you're going to write it all the way to

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the earth i am going to

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stop it though before you

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they've asked me not to

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so here we are approaching the earth

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we're 48 41 minutes out so we're

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approaching the earth very quick uh

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we're now about 15 minutes out screaming

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over

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asia

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just about to hit and you can see the

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impact site just ahead of us on the limb

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of the earth

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okay it went screaming into the

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stratosphere

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generating

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twin vortices tails behind the object as

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it was depositing a tremendous amount of

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kinetic energy in the atmosphere and

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there was a series of high energy

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detonations

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closer to the ground

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that generated shock waves which really

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are the culprit behind the damage that

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so startled the people in russia

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the

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inward

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uh here we see smoke or dust rising

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where a factory wall collapsed inward

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and outward

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here is the aftermath of that collapsed

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wall from a similar perspective and

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here's you can see the debris of the

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wall that collapsed onto the sidewalk

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unfortunately nobody was caught on very

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beneath that debris

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a lot of people were injured but for the

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most part thankfully they were minor

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injuries now

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i was showing you a perspective from the

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outside i have to say in these types of

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events you are not assured safety

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on the interior so i'm going to show you

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a couple of security films

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that

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captured

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i have to defer to nasa tv i was asked

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okay yeah i was asked not to i'm sorry

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um so so here is a video um

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uh uh and i want to start it and you'll

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see a series of security videos that

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illustrate uh what people at work

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just minding their own business uh saw

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whoops it didn't start quite right let

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they quite clearly realized that there

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was something bad going on outside and

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okay now we're going to see a warehouse

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that's a shock wave and an air blast

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and i like the fact that this gentleman

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went over to his colleague and picked

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her up and left very well done

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okay so

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so this obviously was a big event um but

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there's a couple of things i want to say

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about them these stuff is falling onto

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the earth all the time

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and if we step outside on a clear night

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you can often times see meteors crossing

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the sky these little dust sized

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particles

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so the process of material hitting the

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earth is not unique it's not rare it

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happens all the time fortunately most of

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the debris hitting the earth

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is small in size this is a little

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diagram that illustrates the

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consequences of different types of

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material here are the meteors that you

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see burning up in the upper most

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atmosphere when they are small dust

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sized particles larger objects can

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penetrate deeper

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to the surface of the earth sometimes

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they completely catastrophically

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fragment so you cannot

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find any remnants of the object but

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sometimes they'll reach the lower

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atmosphere completely decelerate and

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then fall to the earth as a single

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meteorite

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the more the bigger objects will

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generate lots of smoky trails this is

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something akin to what chelyabinsk did

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can have one or more multiple

282
00:11:03,829 --> 00:11:01,360
fragmentation or have fragmentation

283
00:11:05,750 --> 00:11:03,839
events and shower the ground with a

284
00:11:08,470 --> 00:11:05,760
series of objects

285
00:11:11,030 --> 00:11:08,480
the largest or strongest objects can

286
00:11:13,430 --> 00:11:11,040
penetrate the entire atmosphere hit the

287
00:11:15,350 --> 00:11:13,440
surface and produce a hypervelocity

288
00:11:18,470 --> 00:11:15,360
impact crater so

289
00:11:21,990 --> 00:11:18,480
message one is this is a common process

290
00:11:23,509 --> 00:11:22,000
message two is thankfully we are

291
00:11:25,269 --> 00:11:23,519
surrounded by an atmosphere the

292
00:11:27,670 --> 00:11:25,279
atmosphere is a very important shield

293
00:11:29,350 --> 00:11:27,680
for those of us on earth

294
00:11:31,269 --> 00:11:29,360
as you may recall for those of you are a

295
00:11:32,870 --> 00:11:31,279
little bit older when the astronauts

296
00:11:34,870 --> 00:11:32,880
were walking on the lunar surface they

297
00:11:36,550 --> 00:11:34,880
were walking on on a planetary surface

298
00:11:38,389 --> 00:11:36,560
without an atmosphere and even these

299
00:11:40,389 --> 00:11:38,399
little micrometeoritic objects were

300
00:11:42,710 --> 00:11:40,399
plowing into the surface creating

301
00:11:44,630 --> 00:11:42,720
micrometeoritic impact

302
00:11:46,630 --> 00:11:44,640
craters that were so energetic they were

303
00:11:50,150 --> 00:11:46,640
actually melting parts of the lunar

304
00:11:52,150 --> 00:11:50,160
surface continuously okay so thankfully

305
00:11:54,710 --> 00:11:52,160
we have a atmosphere that protects us

306
00:11:57,190 --> 00:11:54,720
from objects like chelyabinsk otherwise

307
00:11:59,509 --> 00:11:57,200
it would have hit the ground and created

308
00:12:01,110 --> 00:11:59,519
some more damage okay

309
00:12:03,269 --> 00:12:01,120
meteors are something that you can also

310
00:12:04,870 --> 00:12:03,279
see from space i love this picture this

311
00:12:06,550 --> 00:12:04,880
is captured by some of our colleagues

312
00:12:07,509 --> 00:12:06,560
across the street at the johnson space

313
00:12:09,350 --> 00:12:07,519
center

314
00:12:11,030 --> 00:12:09,360
when they were on orbit on the

315
00:12:13,190 --> 00:12:11,040
international space station you can see

316
00:12:16,069 --> 00:12:13,200
this little perseid meteor streaking

317
00:12:18,069 --> 00:12:16,079
into the upper atmosphere and i would

318
00:12:20,389 --> 00:12:18,079
love to know if somebody saw this very

319
00:12:21,829 --> 00:12:20,399
same year on the ground don't know but

320
00:12:23,030 --> 00:12:21,839
it would be fascinating for it to have

321
00:12:24,870 --> 00:12:23,040
been witnessed

322
00:12:25,990 --> 00:12:24,880
coming and going

323
00:12:28,310 --> 00:12:26,000
okay

324
00:12:30,710 --> 00:12:28,320
not all

325
00:12:33,670 --> 00:12:30,720
fragmentation events also come with

326
00:12:35,269 --> 00:12:33,680
shock shock waves and damaging shock

327
00:12:36,069 --> 00:12:35,279
waves and air blasts

328
00:12:37,910 --> 00:12:36,079
so

329
00:12:40,629 --> 00:12:37,920
this is an example these are a few

330
00:12:44,230 --> 00:12:40,639
stones from the portales valley valley

331
00:12:46,870 --> 00:12:44,240
uh event of 1998 in this case several

332
00:12:48,389 --> 00:12:46,880
dozen stones reached the surface of the

333
00:12:50,389 --> 00:12:48,399
earth after

334
00:12:53,110 --> 00:12:50,399
witnesses reported hearing multiple

335
00:12:55,590 --> 00:12:53,120
detonations and seen smoke trails but in

336
00:12:57,910 --> 00:12:55,600
this case the object was smaller the

337
00:13:00,230 --> 00:12:57,920
detonations occurred a little bit higher

338
00:13:01,910 --> 00:13:00,240
and there was no significant damage on

339
00:13:04,150 --> 00:13:01,920
the ground other than

340
00:13:06,389 --> 00:13:04,160
going through the wall of a barn and

341
00:13:07,990 --> 00:13:06,399
digging a few holes in the field and

342
00:13:08,870 --> 00:13:08,000
roads

343
00:13:10,629 --> 00:13:08,880
okay

344
00:13:13,590 --> 00:13:10,639
so now let's drill in a little bit more

345
00:13:14,949 --> 00:13:13,600
about the chelyabinsk properties itself

346
00:13:17,990 --> 00:13:14,959
first of all the diameter of the

347
00:13:19,670 --> 00:13:18,000
asteroid is about 20 meters 66 feet for

348
00:13:20,790 --> 00:13:19,680
those of you who are used to english

349
00:13:22,949 --> 00:13:20,800
units

350
00:13:25,430 --> 00:13:22,959
the asteroid hit the earth with a

351
00:13:28,069 --> 00:13:25,440
velocity of about 19 kilometers per

352
00:13:29,350 --> 00:13:28,079
second that's about 41 000 miles per

353
00:13:31,829 --> 00:13:29,360
hour

354
00:13:35,509 --> 00:13:31,839
most of the kinetic energy was deposited

355
00:13:38,629 --> 00:13:35,519
an altitude of 35 to 25 kilometers above

356
00:13:41,189 --> 00:13:38,639
the surface and the explosive energy of

357
00:13:43,590 --> 00:13:41,199
that event was approximately

358
00:13:45,269 --> 00:13:43,600
or equal to approximately 500 kilotons

359
00:13:46,150 --> 00:13:45,279
of tnt

360
00:13:49,269 --> 00:13:46,160
which is

361
00:13:50,870 --> 00:13:49,279
just fairly substantial number uh the

362
00:13:53,110 --> 00:13:50,880
energy of the bombs that destroyed

363
00:13:55,910 --> 00:13:53,120
hiroshima and nagasaki and world war ii

364
00:13:58,629 --> 00:13:55,920
were about 15 kilotons so this was a big

365
00:14:00,710 --> 00:13:58,639
event again fortunately occurred at a

366
00:14:02,470 --> 00:14:00,720
fairly high altitude

367
00:14:04,310 --> 00:14:02,480
this event is roughly an order of

368
00:14:07,750 --> 00:14:04,320
magnitude more energetic than the

369
00:14:09,189 --> 00:14:07,760
seacoat alien event of 1947 that also

370
00:14:11,590 --> 00:14:09,199
occurred in russia

371
00:14:13,350 --> 00:14:11,600
it's roughly an order of magnitude less

372
00:14:15,189 --> 00:14:13,360
energetic than the tunguska event of

373
00:14:17,990 --> 00:14:15,199
1908

374
00:14:18,949 --> 00:14:18,000
which occurred in siberia

375
00:14:21,189 --> 00:14:18,959
so

376
00:14:23,670 --> 00:14:21,199
russia obviously is a big continental

377
00:14:25,350 --> 00:14:23,680
mass and sees an unusually large amount

378
00:14:27,750 --> 00:14:25,360
of these events because of that surface

379
00:14:29,910 --> 00:14:27,760
area now i want to actually it's

380
00:14:31,829 --> 00:14:29,920
important to say that the estimates of

381
00:14:33,110 --> 00:14:31,839
these past events that cico delane and

382
00:14:35,269 --> 00:14:33,120
negusca

383
00:14:36,949 --> 00:14:35,279
are our best guesses

384
00:14:38,550 --> 00:14:36,959
um even

385
00:14:40,629 --> 00:14:38,560
gusting is a historical event the

386
00:14:43,590 --> 00:14:40,639
records are quite clear on it but there

387
00:14:44,389 --> 00:14:43,600
weren't arrays of devices out there to

388
00:14:46,310 --> 00:14:44,399
measure

389
00:14:49,990 --> 00:14:46,320
the event it was in fact only

390
00:14:52,790 --> 00:14:50,000
investigated years later and so

391
00:14:55,110 --> 00:14:52,800
when we try to evaluate the hazards of

392
00:14:57,829 --> 00:14:55,120
futures impacts it's important to

393
00:15:01,350 --> 00:14:57,839
understand that our database is really

394
00:15:03,350 --> 00:15:01,360
small okay and that really underscores

395
00:15:04,550 --> 00:15:03,360
the importance of the cellular dense

396
00:15:06,389 --> 00:15:04,560
impact of them

397
00:15:08,629 --> 00:15:06,399
it was terrible that people were hurt

398
00:15:10,230 --> 00:15:08,639
but for the first time we have a really

399
00:15:12,870 --> 00:15:10,240
good data point

400
00:15:16,870 --> 00:15:12,880
that relates the type of damage with the

401
00:15:19,110 --> 00:15:16,880
energy of the impact event okay now when

402
00:15:21,189 --> 00:15:19,120
this occurred on february 15th there was

403
00:15:22,389 --> 00:15:21,199
of course a lot of discussion as to what

404
00:15:24,310 --> 00:15:22,399
hit

405
00:15:26,150 --> 00:15:24,320
what entered the earth's atmosphere i've

406
00:15:27,829 --> 00:15:26,160
been telling you it's an asteroid and of

407
00:15:29,670 --> 00:15:27,839
course we now know it's an asteroid but

408
00:15:32,310 --> 00:15:29,680
what were the clues that led us to that

409
00:15:35,350 --> 00:15:32,320
conclusion some of these clues emerged

410
00:15:36,470 --> 00:15:35,360
really quickly uh so what i'm showing

411
00:15:38,550 --> 00:15:36,480
here

412
00:15:41,110 --> 00:15:38,560
are the is the evidence from the impact

413
00:15:43,990 --> 00:15:41,120
velocity and i am plotting

414
00:15:47,030 --> 00:15:44,000
on the y-axis the impact flux as a

415
00:15:49,110 --> 00:15:47,040
consequence of the impact velocity down

416
00:15:51,350 --> 00:15:49,120
here it's in terms of kilometers per

417
00:15:52,550 --> 00:15:51,360
second up here it's in terms of miles

418
00:15:54,710 --> 00:15:52,560
per second

419
00:15:56,310 --> 00:15:54,720
most of the impactors and this is the

420
00:15:59,430 --> 00:15:56,320
follow the gold line most of the

421
00:16:01,749 --> 00:15:59,440
impactors uh that hit the earth

422
00:16:03,910 --> 00:16:01,759
are asteroids and they have an average

423
00:16:05,430 --> 00:16:03,920
impact velocity of 18 kilometers per

424
00:16:09,269 --> 00:16:05,440
second

425
00:16:11,670 --> 00:16:09,279
the earth is also hit by some

426
00:16:13,910 --> 00:16:11,680
short period comets they hit with

427
00:16:15,910 --> 00:16:13,920
velocities from about 30 to 35

428
00:16:17,749 --> 00:16:15,920
kilometers per second and then there's

429
00:16:19,509 --> 00:16:17,759
even a smaller number of long period

430
00:16:22,069 --> 00:16:19,519
comets that occasionally hit the earth

431
00:16:23,670 --> 00:16:22,079
with velocities of 50 to about 55

432
00:16:25,030 --> 00:16:23,680
kilometers per second

433
00:16:26,949 --> 00:16:25,040
on average

434
00:16:29,829 --> 00:16:26,959
the chelyabinsk object that hit the

435
00:16:32,150 --> 00:16:29,839
earth on 15 february 2013 had an

436
00:16:34,790 --> 00:16:32,160
estimated velocity of 19 kilometers per

437
00:16:36,629 --> 00:16:34,800
second which is this red line right here

438
00:16:38,629 --> 00:16:36,639
which suggests that the object was in

439
00:16:40,230 --> 00:16:38,639
fact an asteroid so that was our first

440
00:16:42,389 --> 00:16:40,240
clue

441
00:16:45,269 --> 00:16:42,399
now there was a lot of video with this

442
00:16:47,829 --> 00:16:45,279
object crossing the sky and scientists

443
00:16:50,389 --> 00:16:47,839
in fact people in the public together

444
00:16:51,990 --> 00:16:50,399
on lots of continents began piecing

445
00:16:53,829 --> 00:16:52,000
together the trajectory of that object

446
00:16:55,430 --> 00:16:53,839
through the sky and then they worked

447
00:16:57,350 --> 00:16:55,440
that backward out into space and

448
00:17:00,150 --> 00:16:57,360
calculated a trajectory

449
00:17:02,389 --> 00:17:00,160
or an orbit excuse me out in space and i

450
00:17:04,309 --> 00:17:02,399
show that result here on this diagram

451
00:17:06,549 --> 00:17:04,319
this is the sun the orbit of mercury the

452
00:17:09,029 --> 00:17:06,559
orbit of venus the orbit of earth orbit

453
00:17:10,150 --> 00:17:09,039
of mars and the particular orbit i'm

454
00:17:11,829 --> 00:17:10,160
showing you is the one that was

455
00:17:13,990 --> 00:17:11,839
determined by paul chotis at the jet

456
00:17:16,470 --> 00:17:14,000
propulsion laboratory and you can see

457
00:17:18,069 --> 00:17:16,480
that the orbit of chely events before it

458
00:17:20,710 --> 00:17:18,079
hit the earth

459
00:17:22,630 --> 00:17:20,720
emerged from the asteroid belt okay so

460
00:17:24,309 --> 00:17:22,640
this is clue number two which is

461
00:17:27,110 --> 00:17:24,319
suggestive of an

462
00:17:28,549 --> 00:17:27,120
origin as an asteroid

463
00:17:30,789 --> 00:17:28,559
finally

464
00:17:33,430 --> 00:17:30,799
not too long after the event occurred

465
00:17:35,270 --> 00:17:33,440
people started reporting stones and and

466
00:17:37,270 --> 00:17:35,280
pebbles and so on and so forth that had

467
00:17:39,909 --> 00:17:37,280
actually reached the surface and began

468
00:17:43,110 --> 00:17:39,919
collecting them so let me show you uh

469
00:17:44,710 --> 00:17:43,120
actually an example of a russian citizen

470
00:17:47,029 --> 00:17:44,720
this is not a scientist but simply a

471
00:17:53,669 --> 00:17:47,039
russian citizen who's very curious about

472
00:17:57,029 --> 00:17:55,270
he's going to drill in he's going to

473
00:17:59,110 --> 00:17:57,039
show you a little spot in the snow

474
00:18:01,430 --> 00:17:59,120
there's that little hole okay

475
00:18:04,070 --> 00:18:01,440
something's pierced the snow he's going

476
00:18:06,070 --> 00:18:04,080
to excavate around that hole

477
00:18:10,950 --> 00:18:06,080
and he's going to uncover

478
00:18:16,630 --> 00:18:13,990
and scrape it away now as it turns out

479
00:18:19,590 --> 00:18:16,640
as these objects pierce the snow they

480
00:18:20,950 --> 00:18:19,600
formed a tube and that tube became icy

481
00:18:23,750 --> 00:18:20,960
and they formed these little objects

482
00:18:25,430 --> 00:18:23,760
that the russians call ice carrots

483
00:18:27,190 --> 00:18:25,440
and at the bottom of the ice carrots you

484
00:18:28,870 --> 00:18:27,200
see these little stones isn't that

485
00:18:29,669 --> 00:18:28,880
wonderful okay

486
00:18:34,789 --> 00:18:29,679
so

487
00:18:36,870 --> 00:18:34,799
we can take away all uncertainty uh and

488
00:18:39,190 --> 00:18:36,880
in fact analyses very quickly revealed

489
00:18:40,870 --> 00:18:39,200
that these uh are related to a type of

490
00:18:42,630 --> 00:18:40,880
meteorites that we call ordinary

491
00:18:43,830 --> 00:18:42,640
copyrights that we know for a lot of

492
00:18:45,909 --> 00:18:43,840
other reasons

493
00:18:47,270 --> 00:18:45,919
come from the asteroid belt and i'll say

494
00:18:50,390 --> 00:18:47,280
something more about

495
00:18:52,710 --> 00:18:50,400
those meteorites in a few minutes now as

496
00:18:55,270 --> 00:18:52,720
i said a few minutes ago this is a 20

497
00:18:57,350 --> 00:18:55,280
meter diameter object it's fairly

498
00:18:59,190 --> 00:18:57,360
substantial composed of ordinary

499
00:19:01,510 --> 00:18:59,200
chondrite material

500
00:19:03,510 --> 00:19:01,520
previously the largest documented

501
00:19:04,789 --> 00:19:03,520
explosive fragmentation of an ordinary

502
00:19:06,870 --> 00:19:04,799
chondritic asteroid occurred in

503
00:19:09,270 --> 00:19:06,880
northwestern arizona

504
00:19:10,950 --> 00:19:09,280
seen here in this red circle in an area

505
00:19:13,270 --> 00:19:10,960
called gold basin

506
00:19:15,029 --> 00:19:13,280
that event involved an 8 meter diameter

507
00:19:16,070 --> 00:19:15,039
asteroid so something substantially

508
00:19:18,390 --> 00:19:16,080
smaller

509
00:19:21,669 --> 00:19:18,400
with a kinetic energy equivalent of 5 to

510
00:19:23,990 --> 00:19:21,679
50 kilotons of tnt so something that was

511
00:19:26,310 --> 00:19:24,000
significantly by a factor of ten to one

512
00:19:28,630 --> 00:19:26,320
hundred smarter than the cellular

513
00:19:30,310 --> 00:19:28,640
event nonetheless uh it showered the

514
00:19:32,950 --> 00:19:30,320
surface with several thousand relics of

515
00:19:34,710 --> 00:19:32,960
the asteroid which we collected over a

516
00:19:36,710 --> 00:19:34,720
period of years

517
00:19:38,470 --> 00:19:36,720
and i want to point out that this is

518
00:19:39,909 --> 00:19:38,480
actually an event that occurred quite a

519
00:19:41,669 --> 00:19:39,919
long time ago

520
00:19:43,510 --> 00:19:41,679
so we are extracting clues from the

521
00:19:44,390 --> 00:19:43,520
geological record of these types of

522
00:19:46,710 --> 00:19:44,400
events

523
00:19:48,950 --> 00:19:46,720
over significant portions of geologic

524
00:19:50,789 --> 00:19:48,960
time now

525
00:19:52,390 --> 00:19:50,799
chelyabinsk was dramatic because it did

526
00:19:54,549 --> 00:19:52,400
get low enough in the atmosphere it

527
00:19:56,390 --> 00:19:54,559
contained a lot of kinetic energy and

528
00:19:58,789 --> 00:19:56,400
there was the explosion that generated

529
00:19:59,990 --> 00:19:58,799
the shock waves and air blasts now it's

530
00:20:02,630 --> 00:20:00,000
important to understand that there are

531
00:20:04,870 --> 00:20:02,640
actually two sources of the shock waves

532
00:20:06,390 --> 00:20:04,880
in the air blast the first one has to do

533
00:20:07,830 --> 00:20:06,400
with the ballistic bite of that object

534
00:20:10,230 --> 00:20:07,840
through the atmosphere and that's what

535
00:20:11,750 --> 00:20:10,240
this first bullet actually addresses

536
00:20:13,350 --> 00:20:11,760
shock waves are produced by objects

537
00:20:15,430 --> 00:20:13,360
moving faster than the speed of sound

538
00:20:17,430 --> 00:20:15,440
i.e mach 1

539
00:20:19,430 --> 00:20:17,440
impacting near-earth asteroids penetrate

540
00:20:22,390 --> 00:20:19,440
the atmosphere with a speed equal to or

541
00:20:24,630 --> 00:20:22,400
in excess of 11.2 kilometers per second

542
00:20:27,110 --> 00:20:24,640
that's more than 25 000 miles per hour

543
00:20:29,430 --> 00:20:27,120
or greater than mach 35

544
00:20:31,350 --> 00:20:29,440
which produces a ballistic shock wave

545
00:20:35,510 --> 00:20:31,360
the chelyabinsk near earth asteroid was

546
00:20:37,590 --> 00:20:35,520
moving at mach 60 to 61.

547
00:20:39,270 --> 00:20:37,600
now a second

548
00:20:41,430 --> 00:20:39,280
shock wave is produced by the

549
00:20:43,510 --> 00:20:41,440
catastrophic explosion

550
00:20:46,470 --> 00:20:43,520
okay so that's just like a bomb going

551
00:20:48,950 --> 00:20:46,480
off anywhere that produces a radiating

552
00:20:51,430 --> 00:20:48,960
shock wave that can reach the surface of

553
00:20:52,630 --> 00:20:51,440
the earth if it occurs above the surface

554
00:20:54,630 --> 00:20:52,640
of the earth

555
00:20:56,870 --> 00:20:54,640
and those shock waves are accompanied by

556
00:20:58,950 --> 00:20:56,880
high velocity air blaster high velocity

557
00:21:01,270 --> 00:20:58,960
winds similar effects were measured

558
00:21:04,070 --> 00:21:01,280
around nuclear explosion test lights

559
00:21:05,830 --> 00:21:04,080
this is an example of trees around a

560
00:21:08,070 --> 00:21:05,840
united states test

561
00:21:10,230 --> 00:21:08,080
during the cold war and you can see that

562
00:21:12,070 --> 00:21:10,240
the shock wave and the air blast

563
00:21:13,430 --> 00:21:12,080
actually is picking up a lot of dust

564
00:21:15,909 --> 00:21:13,440
blowing it and

565
00:21:17,909 --> 00:21:15,919
blending over trees now the tunduska

566
00:21:20,310 --> 00:21:17,919
impact event which i've mentioned

567
00:21:23,990 --> 00:21:20,320
once and we'll refer to again the event

568
00:21:25,830 --> 00:21:24,000
of 1908 was so energetic that when it uh

569
00:21:28,230 --> 00:21:25,840
the shockwave and airblast encountered

570
00:21:31,430 --> 00:21:28,240
the forest in siberia it snapped those

571
00:21:34,310 --> 00:21:31,440
trees over like toothpicks over a region

572
00:21:36,470 --> 00:21:34,320
without two thousand square kilometers

573
00:21:39,190 --> 00:21:36,480
okay now

574
00:21:41,029 --> 00:21:39,200
this is a diagram that illustrates uh

575
00:21:44,470 --> 00:21:41,039
the consequence of the shock wave as it

576
00:21:46,470 --> 00:21:44,480
radiates from the point of origin

577
00:21:48,789 --> 00:21:46,480
so this is increasing pressure over

578
00:21:51,669 --> 00:21:48,799
pressure and as a function of distance

579
00:21:53,590 --> 00:21:51,679
from that origin and not surprisingly

580
00:21:56,630 --> 00:21:53,600
the shock wave is more intense the

581
00:21:58,630 --> 00:21:56,640
closer you are to the impact and as time

582
00:22:01,830 --> 00:21:58,640
progresses and the odd the shock wave

583
00:22:02,870 --> 00:22:01,840
passes over a larger and larger area of

584
00:22:04,710 --> 00:22:02,880
the earth

585
00:22:07,029 --> 00:22:04,720
the energy or the magnitude of that

586
00:22:08,070 --> 00:22:07,039
shock wave decreases

587
00:22:11,110 --> 00:22:08,080
now

588
00:22:14,310 --> 00:22:11,120
let's talk about what shock waves and

589
00:22:16,789 --> 00:22:14,320
air blasts have done at some other known

590
00:22:19,190 --> 00:22:16,799
geologic events

591
00:22:21,510 --> 00:22:19,200
the best preserve and i think the most

592
00:22:23,350 --> 00:22:21,520
dramatic near-earth asteroid impact site

593
00:22:25,190 --> 00:22:23,360
is behringer or meteor crater in

594
00:22:26,950 --> 00:22:25,200
northern arizona if you've not been

595
00:22:29,190 --> 00:22:26,960
there you need to go there okay it's

596
00:22:31,029 --> 00:22:29,200
just down the road from the grand canyon

597
00:22:33,830 --> 00:22:31,039
so when you go to the grand canyon make

598
00:22:37,270 --> 00:22:33,840
a stop this is the crater it's 1.2

599
00:22:38,950 --> 00:22:37,280
kilometers in diameter okay uh the the

600
00:22:40,950 --> 00:22:38,960
guides there like to point out that if

601
00:22:42,470 --> 00:22:40,960
you had stood the washington monument on

602
00:22:44,710 --> 00:22:42,480
the floor of the crater

603
00:22:46,310 --> 00:22:44,720
the tip of the monument would just reach

604
00:22:47,430 --> 00:22:46,320
the rim

605
00:22:48,710 --> 00:22:47,440
and

606
00:22:49,909 --> 00:22:48,720
this was a

607
00:22:51,990 --> 00:22:49,919
larger

608
00:22:54,390 --> 00:22:52,000
impact event the object obviously

609
00:22:56,549 --> 00:22:54,400
reached the ground but as i'll discuss a

610
00:22:58,470 --> 00:22:56,559
little bit later the object wasn't that

611
00:22:59,830 --> 00:22:58,480
much bigger than the chelyabinsk one so

612
00:23:01,430 --> 00:22:59,840
that's actually important to keep in

613
00:23:04,230 --> 00:23:01,440
mind when you're trying to think about

614
00:23:06,470 --> 00:23:04,240
the evaluate the hazard disease types of

615
00:23:07,909 --> 00:23:06,480
objects okay so let's talk about what

616
00:23:10,470 --> 00:23:07,919
meteor crate what happened at meteor

617
00:23:11,909 --> 00:23:10,480
crater this is a satellite view it isn't

618
00:23:13,430 --> 00:23:11,919
actually it's a space shuttle view this

619
00:23:16,390 --> 00:23:13,440
is from columbia

620
00:23:18,149 --> 00:23:16,400
uh and here is the 1.2 kilometer crater

621
00:23:21,430 --> 00:23:18,159
right here in the center of the bullseye

622
00:23:23,350 --> 00:23:21,440
okay now uh in small events like this

623
00:23:25,990 --> 00:23:23,360
one it's hard to imagine this is a small

624
00:23:28,789 --> 00:23:26,000
event but in the scheme of things it is

625
00:23:30,630 --> 00:23:28,799
a fireball shockwave and air blast are

626
00:23:33,510 --> 00:23:30,640
the major environmental effects this is

627
00:23:36,470 --> 00:23:33,520
not the size of the vent that produces

628
00:23:38,149 --> 00:23:36,480
global climatic changes mass extinctions

629
00:23:40,070 --> 00:23:38,159
or anything of that sort

630
00:23:42,070 --> 00:23:40,080
nonetheless the blast effect was

631
00:23:44,710 --> 00:23:42,080
immediately lethal for human sized

632
00:23:48,149 --> 00:23:44,720
animals within the inner six kilometer

633
00:23:50,470 --> 00:23:48,159
diameter circle that circle right there

634
00:23:52,789 --> 00:23:50,480
severe lung damage

635
00:23:54,549 --> 00:23:52,799
uh would occur within the next 10 to 12

636
00:23:57,029 --> 00:23:54,559
kilometer diameter circle due to

637
00:23:59,350 --> 00:23:57,039
pressure pulse alone and animals would

638
00:24:02,390 --> 00:23:59,360
be severely injured and unlikely to

639
00:24:05,350 --> 00:24:02,400
survive with that within that region

640
00:24:08,470 --> 00:24:05,360
now winds and would have exceeded 15

641
00:24:10,470 --> 00:24:08,480
kilometers 1500 excuse me 1500

642
00:24:11,510 --> 00:24:10,480
kilometers per hour within the inner

643
00:24:14,310 --> 00:24:11,520
circle

644
00:24:16,950 --> 00:24:14,320
and still exceed 100 kilometers per hour

645
00:24:19,110 --> 00:24:16,960
at radial distances of 25 kilometers

646
00:24:21,190 --> 00:24:19,120
which is this third circle here the

647
00:24:24,630 --> 00:24:21,200
outermost circle that i portrayed there

648
00:24:26,630 --> 00:24:24,640
at 50 kilometer uh 50 kilometers

649
00:24:28,950 --> 00:24:26,640
represents the outer limit of severe to

650
00:24:31,669 --> 00:24:28,960
moderate damage trees and any human

651
00:24:32,390 --> 00:24:31,679
structures of comparable strength to

652
00:24:34,149 --> 00:24:32,400
trees

653
00:24:36,390 --> 00:24:34,159
and i say that because at this point at

654
00:24:38,230 --> 00:24:36,400
the time of this impact event 50 000

655
00:24:40,149 --> 00:24:38,240
years ago there weren't humans in the

656
00:24:43,510 --> 00:24:40,159
vicinity and there certainly weren't any

657
00:24:45,269 --> 00:24:43,520
houses or anything of that sort

658
00:24:46,950 --> 00:24:45,279
in contrast to what you'll sometimes

659
00:24:47,990 --> 00:24:46,960
hear visitors say

660
00:24:49,269 --> 00:24:48,000
on the rim of the crater it's

661
00:24:53,029 --> 00:24:49,279
fascinating

662
00:24:55,110 --> 00:24:53,039
okay now this being 50 000 years ago

663
00:24:58,070 --> 00:24:55,120
the landscape was different in fact the

664
00:24:59,430 --> 00:24:58,080
climate was different we had cool cooler

665
00:25:01,350 --> 00:24:59,440
and and wetter conditions we are

666
00:25:03,590 --> 00:25:01,360
actually were in the ice age

667
00:25:05,750 --> 00:25:03,600
uh the animals that would have adorned

668
00:25:08,630 --> 00:25:05,760
the landscape are mammoths and mastodons

669
00:25:11,750 --> 00:25:08,640
giant grounds sloths and bears beating

670
00:25:12,549 --> 00:25:11,760
and browsing and hunting okay

671
00:25:14,390 --> 00:25:12,559
uh

672
00:25:16,549 --> 00:25:14,400
you'll see that red circle

673
00:25:18,549 --> 00:25:16,559
that represents uh where the fireball

674
00:25:20,870 --> 00:25:18,559
would have scorched plants to animals up

675
00:25:23,990 --> 00:25:20,880
to a distance of 10 kilometers

676
00:25:26,789 --> 00:25:24,000
the yellow zone represents where large

677
00:25:29,269 --> 00:25:26,799
animals were killed or wounded by a

678
00:25:31,750 --> 00:25:29,279
pressure pulse and an air blast i mean

679
00:25:33,990 --> 00:25:31,760
for example imagine this

680
00:25:35,430 --> 00:25:34,000
pressure pulse and an air blast hit

681
00:25:38,070 --> 00:25:35,440
going over the landscape picking up

682
00:25:40,149 --> 00:25:38,080
sticks and stones and basically creating

683
00:25:41,590 --> 00:25:40,159
the fuselage or a shotgun blast that

684
00:25:42,390 --> 00:25:41,600
would have impaled

685
00:25:45,190 --> 00:25:42,400
organ

686
00:25:47,510 --> 00:25:45,200
animals living across the surface so

687
00:25:50,390 --> 00:25:47,520
even animals that were wounded and not

688
00:25:52,950 --> 00:25:50,400
killed directly may have had a hard time

689
00:25:54,470 --> 00:25:52,960
surviving afterwards hurricane force

690
00:25:56,310 --> 00:25:54,480
winds would have then extended up to a

691
00:25:58,390 --> 00:25:56,320
distances of 30 kilometers in all

692
00:26:01,909 --> 00:25:58,400
directions which is represented

693
00:26:04,310 --> 00:26:01,919
by that blue circle okay

694
00:26:07,029 --> 00:26:04,320
now as i said that occurred 50 000 years

695
00:26:09,269 --> 00:26:07,039
ago there were no humans in the region

696
00:26:12,870 --> 00:26:09,279
but it's important to note that if such

697
00:26:15,350 --> 00:26:12,880
an event were to occur today it has

698
00:26:18,070 --> 00:26:15,360
the capability of completely decimating

699
00:26:20,549 --> 00:26:18,080
a population of a modern uh

700
00:26:22,390 --> 00:26:20,559
city like kansas city so here is a

701
00:26:24,070 --> 00:26:22,400
outline of the metropolitan area of

702
00:26:25,510 --> 00:26:24,080
kansas city

703
00:26:27,430 --> 00:26:25,520
that is the

704
00:26:28,390 --> 00:26:27,440
circle represents

705
00:26:30,950 --> 00:26:28,400
the

706
00:26:33,029 --> 00:26:30,960
zone of severe to moderate damage

707
00:26:34,950 --> 00:26:33,039
anything in that zone would essentially

708
00:26:37,269 --> 00:26:34,960
be annihilated

709
00:26:39,909 --> 00:26:37,279
okay

710
00:26:42,470 --> 00:26:39,919
larger impact events affect larger

711
00:26:43,909 --> 00:26:42,480
regions this is a picture of eastern

712
00:26:45,669 --> 00:26:43,919
canada

713
00:26:47,669 --> 00:26:45,679
in the center of the bullseye is a

714
00:26:51,510 --> 00:26:47,679
crater called manical wagon it's about

715
00:26:53,990 --> 00:26:51,520
100 kilometers in diameter

716
00:26:56,789 --> 00:26:54,000
and the white circle represents

717
00:26:58,470 --> 00:26:56,799
the region over which

718
00:27:01,590 --> 00:26:58,480
buildings and structures if they were to

719
00:27:04,149 --> 00:27:01,600
occur there would have been destroyed

720
00:27:06,789 --> 00:27:04,159
so as you can see it's a rather large

721
00:27:09,350 --> 00:27:06,799
area over a diameter of about 1100

722
00:27:11,350 --> 00:27:09,360
kilometers fortunately i've said this

723
00:27:14,310 --> 00:27:11,360
once before and i'll say it again

724
00:27:17,909 --> 00:27:14,320
larger impact events occur far less

725
00:27:20,149 --> 00:27:17,919
frequently than small ones which is good

726
00:27:22,149 --> 00:27:20,159
and really good when you start to step

727
00:27:24,549 --> 00:27:22,159
up to chick sleep size impact events

728
00:27:26,549 --> 00:27:24,559
which are dinosaur killing impact events

729
00:27:28,549 --> 00:27:26,559
mass extinction style impact events

730
00:27:31,669 --> 00:27:28,559
unfortunately for us these occur on

731
00:27:32,549 --> 00:27:31,679
average only once per 100 million years

732
00:27:34,389 --> 00:27:32,559
okay

733
00:27:37,350 --> 00:27:34,399
in this case

734
00:27:39,269 --> 00:27:37,360
um a severe air blast represented by the

735
00:27:40,950 --> 00:27:39,279
red zone flattened would have flattened

736
00:27:42,870 --> 00:27:40,960
any force out to a distance of about

737
00:27:44,950 --> 00:27:42,880
1500 kilometers

738
00:27:47,029 --> 00:27:44,960
gale to hurricane force winds would have

739
00:27:49,430 --> 00:27:47,039
extended over the entire southern part

740
00:27:53,029 --> 00:27:49,440
of the north american continent as

741
00:27:55,350 --> 00:27:53,039
outlined by that yellow circle

742
00:27:58,549 --> 00:27:55,360
in this case these are actually minor

743
00:27:59,510 --> 00:27:58,559
consequences of the impact event in this

744
00:28:01,669 --> 00:27:59,520
case

745
00:28:02,789 --> 00:28:01,679
the impact event was so large that had

746
00:28:05,350 --> 00:28:02,799
global

747
00:28:07,110 --> 00:28:05,360
effects that extinguished most life on

748
00:28:09,590 --> 00:28:07,120
earth at that time

749
00:28:11,350 --> 00:28:09,600
65 million years ago okay

750
00:28:12,870 --> 00:28:11,360
so this is a little chart to kind of

751
00:28:14,710 --> 00:28:12,880
illustrate what i've just said in the

752
00:28:18,870 --> 00:28:14,720
last slides

753
00:28:21,430 --> 00:28:18,880
the area affected uh by the blast

754
00:28:23,110 --> 00:28:21,440
uh increases as the impact energy

755
00:28:24,950 --> 00:28:23,120
increases and so you see several things

756
00:28:28,070 --> 00:28:24,960
here plotted there's behringer meteor

757
00:28:30,070 --> 00:28:28,080
crater uh there's uh the reese crater in

758
00:28:31,590 --> 00:28:30,080
germany there's wagon which i showed you

759
00:28:34,149 --> 00:28:31,600
in canada and here's the chick-fil-a

760
00:28:35,350 --> 00:28:34,159
impact event in mexico that affected the

761
00:28:38,230 --> 00:28:35,360
entire world

762
00:28:41,269 --> 00:28:38,240
shelia bentz you can see is at the

763
00:28:45,350 --> 00:28:41,279
extreme small end of the types of events

764
00:28:47,430 --> 00:28:45,360
that produce air blast okay

765
00:28:49,510 --> 00:28:47,440
so at some level you look at this chart

766
00:28:51,830 --> 00:28:49,520
and say okay they're not bad

767
00:28:53,990 --> 00:28:51,840
inconsequential at some level

768
00:28:55,830 --> 00:28:54,000
but it's important to also realize that

769
00:28:58,389 --> 00:28:55,840
as the world's population grows and

770
00:29:00,310 --> 00:28:58,399
occupies a larger fraction of earth's

771
00:29:02,470 --> 00:29:00,320
surface events like chely events will

772
00:29:05,350 --> 00:29:02,480
potentially affect more people so that

773
00:29:06,470 --> 00:29:05,360
isn't something i think to keep in mind

774
00:29:07,590 --> 00:29:06,480
okay

775
00:29:09,269 --> 00:29:07,600
now

776
00:29:12,149 --> 00:29:09,279
you don't just have to look at the

777
00:29:15,350 --> 00:29:12,159
geologic past

778
00:29:19,430 --> 00:29:17,909
see examples of these type of events

779
00:29:20,870 --> 00:29:19,440
on this is the modification of the

780
00:29:22,789 --> 00:29:20,880
diagram i showed you earlier i've

781
00:29:24,470 --> 00:29:22,799
actually now put on here the

782
00:29:25,830 --> 00:29:24,480
trajectories of several relatively

783
00:29:27,750 --> 00:29:25,840
recent events

784
00:29:30,070 --> 00:29:27,760
here's chelyabinsk itself coming in

785
00:29:32,789 --> 00:29:30,080
rather shallowly detonating here with a

786
00:29:36,149 --> 00:29:32,799
fat blast of 500 kilotons

787
00:29:38,310 --> 00:29:36,159
just the year before in 2012

788
00:29:40,070 --> 00:29:38,320
the sutter's mill meteoroid detonated

789
00:29:41,350 --> 00:29:40,080
over california how many people remember

790
00:29:44,310 --> 00:29:41,360
hearing about that

791
00:29:47,750 --> 00:29:44,320
okay that had the uh energy of about

792
00:29:50,470 --> 00:29:47,760
four kilotons and then in 2008 we had

793
00:29:53,190 --> 00:29:50,480
another asteroid come whizzing in this

794
00:29:54,950 --> 00:29:53,200
one actually was detected before it hit

795
00:29:56,870 --> 00:29:54,960
and so there were prediction predictions

796
00:29:59,510 --> 00:29:56,880
as to where it would burst and in fact

797
00:30:02,710 --> 00:29:59,520
it did burst with a one kiloton blast uh

798
00:30:05,590 --> 00:30:02,720
over northern sudan okay

799
00:30:07,750 --> 00:30:05,600
so these events are something that occur

800
00:30:09,590 --> 00:30:07,760
on a relatively frequent time scale okay

801
00:30:11,269 --> 00:30:09,600
now let's let's look at the asteroid

802
00:30:13,430 --> 00:30:11,279
itself okay we have all these meteoritic

803
00:30:15,350 --> 00:30:13,440
fragments of it here is a picture just

804
00:30:16,630 --> 00:30:15,360
rotated of one of these fragments it's a

805
00:30:19,909 --> 00:30:16,640
beautiful rock

806
00:30:23,029 --> 00:30:19,919
um you can see that it is it's a breccia

807
00:30:25,830 --> 00:30:23,039
what i mean by a brecht it it is a rock

808
00:30:27,190 --> 00:30:25,840
that is composed of broken fragments of

809
00:30:29,190 --> 00:30:27,200
older rocks

810
00:30:32,230 --> 00:30:29,200
and they are cross-cut by these dark

811
00:30:35,110 --> 00:30:32,240
black veins these veins are material of

812
00:30:37,909 --> 00:30:35,120
shock-melted uh portions of the asteroid

813
00:30:40,230 --> 00:30:37,919
that were created in an impact event on

814
00:30:43,590 --> 00:30:40,240
the asteroid long before it encountered

815
00:30:46,470 --> 00:30:43,600
the earth okay this retriation process

816
00:30:47,750 --> 00:30:46,480
uh probably is responsible for reducing

817
00:30:50,310 --> 00:30:47,760
the structural integrity of the

818
00:30:52,310 --> 00:30:50,320
meteoroid and made it more susceptible

819
00:30:54,710 --> 00:30:52,320
for catastrophic fragmentation in the

820
00:30:57,190 --> 00:30:54,720
earth's atmosphere and this is something

821
00:30:59,750 --> 00:30:57,200
that's been argued on the basis of other

822
00:31:02,470 --> 00:30:59,760
uh meteoritic materials that have fallen

823
00:31:03,190 --> 00:31:02,480
to the earth now scientists love to take

824
00:31:05,669 --> 00:31:03,200
these

825
00:31:08,149 --> 00:31:05,679
thin slices through rocks and this is an

826
00:31:09,269 --> 00:31:08,159
example of that through the chelyabinsk

827
00:31:10,870 --> 00:31:09,279
meteorite

828
00:31:13,029 --> 00:31:10,880
and then we put it on a microscope and

829
00:31:14,630 --> 00:31:13,039
this allows us to see the microscopic

830
00:31:16,630 --> 00:31:14,640
texture of the interior and the

831
00:31:18,710 --> 00:31:16,640
meteoritis in the audience are going to

832
00:31:20,070 --> 00:31:18,720
be drawn immediately to these circular

833
00:31:21,830 --> 00:31:20,080
objects that are scattered here and

834
00:31:24,789 --> 00:31:21,840
there throughout the object

835
00:31:27,990 --> 00:31:24,799
these are conduits these represent

836
00:31:30,149 --> 00:31:28,000
molten droplets of rock fiery rain that

837
00:31:33,029 --> 00:31:30,159
once existed in the solar nebula this

838
00:31:35,509 --> 00:31:33,039
disk of dust and graft gas that used to

839
00:31:39,190 --> 00:31:35,519
circulate around the sun long before

840
00:31:41,669 --> 00:31:39,200
planets accreted okay

841
00:31:43,990 --> 00:31:41,679
these chondrules are eventually accreted

842
00:31:45,909 --> 00:31:44,000
to form small planetesimals and those in

843
00:31:48,549 --> 00:31:45,919
turn eventually accreted to form the

844
00:31:50,789 --> 00:31:48,559
larger planets like earth

845
00:31:52,950 --> 00:31:50,799
that material after accreted into some a

846
00:31:54,710 --> 00:31:52,960
small planetary body was then affected

847
00:31:57,350 --> 00:31:54,720
by an impact event and it created these

848
00:31:59,269 --> 00:31:57,360
dark black channels of impact melt

849
00:32:02,230 --> 00:31:59,279
that cross cut the sample

850
00:32:04,789 --> 00:32:02,240
other parts of this meteoroid

851
00:32:07,029 --> 00:32:04,799
are completely black okay none of those

852
00:32:08,950 --> 00:32:07,039
white fragments survive

853
00:32:11,350 --> 00:32:08,960
and those black regions are visible in

854
00:32:13,029 --> 00:32:11,360
both the microscopic thin section and

855
00:32:14,630 --> 00:32:13,039
actually in whole specimens this is a

856
00:32:16,470 --> 00:32:14,640
centimeter cubed

857
00:32:18,549 --> 00:32:16,480
and this material has been severely

858
00:32:20,470 --> 00:32:18,559
shock damaged and melted by a

859
00:32:23,029 --> 00:32:20,480
pre-existing impact event on the

860
00:32:25,909 --> 00:32:23,039
asteroid before it actually encountered

861
00:32:27,590 --> 00:32:25,919
the earth okay now

862
00:32:30,310 --> 00:32:27,600
this is a picture to kind of illustrate

863
00:32:32,870 --> 00:32:30,320
the processes that this meteorite or the

864
00:32:34,070 --> 00:32:32,880
meat the parent body suffered before it

865
00:32:36,070 --> 00:32:34,080
encountered the earth it came from the

866
00:32:37,590 --> 00:32:36,080
asteroid belt and in the asteroid belt

867
00:32:39,509 --> 00:32:37,600
the asteroids are bumping into each

868
00:32:41,350 --> 00:32:39,519
other and any picture of the asteroid

869
00:32:43,590 --> 00:32:41,360
that you see returned by nasa spacecraft

870
00:32:46,070 --> 00:32:43,600
or other agency spacecraft then you will

871
00:32:48,710 --> 00:32:46,080
inevitably see a surface that has been

872
00:32:50,870 --> 00:32:48,720
pockmarked or affected by collisional

873
00:32:52,230 --> 00:32:50,880
processes here in fact you can see an

874
00:32:54,149 --> 00:32:52,240
impact uh

875
00:32:55,430 --> 00:32:54,159
illustrated uh

876
00:32:57,190 --> 00:32:55,440
and and

877
00:32:58,870 --> 00:32:57,200
going on and i i should say i want to

878
00:33:01,430 --> 00:32:58,880
thank dan durda who is actually the

879
00:33:03,350 --> 00:33:01,440
artist that uh reconstructed these some

880
00:33:05,190 --> 00:33:03,360
of these impact events are so

881
00:33:07,909 --> 00:33:05,200
catastrophic the object might actually

882
00:33:10,389 --> 00:33:07,919
pull apart and reassemble uh forming uh

883
00:33:12,230 --> 00:33:10,399
rubble piles now

884
00:33:13,190 --> 00:33:12,240
this is a picture of the asteroid belt

885
00:33:15,110 --> 00:33:13,200
okay

886
00:33:16,950 --> 00:33:15,120
we have the earth and the moon here's

887
00:33:19,590 --> 00:33:16,960
mars here's jupiter and the asteroid

888
00:33:22,070 --> 00:33:19,600
belt is lined between mars and jupiter

889
00:33:24,710 --> 00:33:22,080
uh asteroids can survive for billions of

890
00:33:25,830 --> 00:33:24,720
years in the asteroid belt up to 4.5

891
00:33:27,909 --> 00:33:25,840
billion years

892
00:33:30,789 --> 00:33:27,919
every once in a while those asteroids

893
00:33:32,789 --> 00:33:30,799
can migrate or will migrate into these

894
00:33:35,909 --> 00:33:32,799
channels you can see there's these gulfs

895
00:33:38,789 --> 00:33:35,919
these gaps they're called kirkwood gaps

896
00:33:40,470 --> 00:33:38,799
where asteroids when they reach those

897
00:33:43,909 --> 00:33:40,480
positions in the asteroid belt are

898
00:33:45,750 --> 00:33:43,919
affected gravitationally by jupiter

899
00:33:47,750 --> 00:33:45,760
and the orbits are perturbed so instead

900
00:33:49,830 --> 00:33:47,760
of having a nice circular orbit around

901
00:33:52,389 --> 00:33:49,840
the sun they're perturbed into an

902
00:33:54,149 --> 00:33:52,399
elliptical orbit that crosses

903
00:33:56,789 --> 00:33:54,159
the orbits of the inner solar system

904
00:33:59,190 --> 00:33:56,799
planets like mars earth venus mercury

905
00:34:01,909 --> 00:33:59,200
and once they cross those orbits they

906
00:34:03,590 --> 00:34:01,919
can collide with the planets so that

907
00:34:05,830 --> 00:34:03,600
happened to chelyabinsk at some point in

908
00:34:07,269 --> 00:34:05,840
time and put it on a collision course

909
00:34:09,270 --> 00:34:07,279
with earth

910
00:34:11,030 --> 00:34:09,280
okay now

911
00:34:14,230 --> 00:34:11,040
we actually know quite a lot about the

912
00:34:16,550 --> 00:34:14,240
asteroids uh and near-earth asteroids

913
00:34:18,629 --> 00:34:16,560
to be more precise we have fifty

914
00:34:20,869 --> 00:34:18,639
thousand samples an era of asteroids in

915
00:34:23,669 --> 00:34:20,879
our collections every meteorite's near

916
00:34:26,230 --> 00:34:23,679
an asteroid okay so we know something

917
00:34:27,829 --> 00:34:26,240
about uh those those objects and how

918
00:34:29,349 --> 00:34:27,839
they were processed or evolved in the

919
00:34:31,669 --> 00:34:29,359
asteroid belt we know something about

920
00:34:33,510 --> 00:34:31,679
how those objects evolve once they get

921
00:34:36,149 --> 00:34:33,520
into earth crossing orbits and we know

922
00:34:37,829 --> 00:34:36,159
something about uh

923
00:34:40,069 --> 00:34:37,839
the collisional processes when they

924
00:34:42,230 --> 00:34:40,079
actually do encounter the earth now most

925
00:34:43,669 --> 00:34:42,240
of those samples most of those 50 000

926
00:34:44,790 --> 00:34:43,679
samples are what we call ordinary

927
00:34:47,190 --> 00:34:44,800
chondrites

928
00:34:49,349 --> 00:34:47,200
that's the type of material chelyabinsk

929
00:34:51,270 --> 00:34:49,359
is composed of okay now there's three

930
00:34:52,869 --> 00:34:51,280
types of ordinary chondrites there is

931
00:34:54,230 --> 00:34:52,879
something called type h

932
00:34:56,230 --> 00:34:54,240
and i'm not going to worry too much

933
00:34:57,589 --> 00:34:56,240
about the distinctions between these

934
00:34:59,910 --> 00:34:57,599
just understand that there are some

935
00:35:02,069 --> 00:34:59,920
compositional differences that suggest

936
00:35:03,510 --> 00:35:02,079
they came from three different parent

937
00:35:05,589 --> 00:35:03,520
bodies okay

938
00:35:07,510 --> 00:35:05,599
so there's a type h ordinary chondroitin

939
00:35:09,829 --> 00:35:07,520
type l ordinary chondrites and the type

940
00:35:12,310 --> 00:35:09,839
ll ordinary chondrites

941
00:35:14,069 --> 00:35:12,320
and our analyses and analyses by teams

942
00:35:16,790 --> 00:35:14,079
around the world have found that

943
00:35:20,630 --> 00:35:16,800
t'chelyabinsk object is derived from the

944
00:35:23,109 --> 00:35:20,640
ll parent body we have almost 6 000

945
00:35:24,710 --> 00:35:23,119
other samples from that parent body so

946
00:35:27,430 --> 00:35:24,720
we can actually piece together a pretty

947
00:35:29,030 --> 00:35:27,440
good story about what that

948
00:35:31,349 --> 00:35:29,040
object experienced and hearing it back

949
00:35:33,349 --> 00:35:31,359
is it's one of one of those six thousand

950
00:35:35,030 --> 00:35:33,359
samples this is the perigold uh

951
00:35:37,990 --> 00:35:35,040
meteorite and i love this one because

952
00:35:39,910 --> 00:35:38,000
first of all it's a it's a large mass

953
00:35:41,750 --> 00:35:39,920
if you have gone to the

954
00:35:43,750 --> 00:35:41,760
natural history museum the smithsonian

955
00:35:45,190 --> 00:35:43,760
in washington dc and gone to the meteor

956
00:35:47,270 --> 00:35:45,200
exhibit you've seen it you may not

957
00:35:49,670 --> 00:35:47,280
remember it but you've seen it

958
00:35:51,829 --> 00:35:49,680
and you can see here we have relic

959
00:35:54,069 --> 00:35:51,839
fragments of the asteroid that were

960
00:35:56,470 --> 00:35:54,079
caught up in an impact cratering event

961
00:35:58,950 --> 00:35:56,480
on this parent asteroid and it like

962
00:36:01,430 --> 00:35:58,960
chelyabinsk is cross-cut with these dark

963
00:36:04,550 --> 00:36:01,440
impact melted shock veins so in many

964
00:36:06,630 --> 00:36:04,560
ways perigold has a lot of similarities

965
00:36:08,790 --> 00:36:06,640
to chelyabinsk okay

966
00:36:11,349 --> 00:36:08,800
because we have that collection of

967
00:36:13,910 --> 00:36:11,359
meteorites from the same parent body as

968
00:36:15,990 --> 00:36:13,920
chelyabinsk we can begin to piece

969
00:36:17,990 --> 00:36:16,000
together the collisional history of that

970
00:36:19,349 --> 00:36:18,000
parent body and this is something that

971
00:36:21,750 --> 00:36:19,359
i've been doing with tim swindle at the

972
00:36:22,950 --> 00:36:21,760
university of arizona and a student that

973
00:36:25,349 --> 00:36:22,960
tim had

974
00:36:27,589 --> 00:36:25,359
we've been analyzed every single impact

975
00:36:29,589 --> 00:36:27,599
melted ordinary chondrite or ll ordinary

976
00:36:32,950 --> 00:36:29,599
chondrite we can get our hands on and

977
00:36:35,109 --> 00:36:32,960
what we found is a large number of them

978
00:36:38,870 --> 00:36:35,119
were involved in impact cratering events

979
00:36:41,270 --> 00:36:38,880
3.9 to 4.4 billion years ago okay

980
00:36:43,430 --> 00:36:41,280
then there's a large gap

981
00:36:45,589 --> 00:36:43,440
in our age distribution which suggests

982
00:36:47,670 --> 00:36:45,599
there were few impacts on that parent

983
00:36:49,750 --> 00:36:47,680
body for a period of about two billion

984
00:36:51,910 --> 00:36:49,760
years and then over the last two billion

985
00:36:53,750 --> 00:36:51,920
years there have been scattered impact

986
00:36:55,430 --> 00:36:53,760
events affecting the surface of that

987
00:36:56,950 --> 00:36:55,440
object one of those probably is

988
00:36:59,190 --> 00:36:56,960
responsible for jet is owning what

989
00:37:01,270 --> 00:36:59,200
became chelyabinsk okay

990
00:37:03,829 --> 00:37:01,280
now more recently we can begin to

991
00:37:05,430 --> 00:37:03,839
analyze chelyabinsk itself okay and so

992
00:37:06,950 --> 00:37:05,440
here are some data that's just appeared

993
00:37:08,630 --> 00:37:06,960
in the literature

994
00:37:11,430 --> 00:37:08,640
our russian colleagues

995
00:37:13,510 --> 00:37:11,440
have determined the age of that black

996
00:37:16,349 --> 00:37:13,520
shock melted veins running through the

997
00:37:19,030 --> 00:37:16,359
sample or produced an impact event

998
00:37:21,270 --> 00:37:19,040
4.452 billion years ago just before the

999
00:37:23,510 --> 00:37:21,280
pulse that tim swindle and i

1000
00:37:26,230 --> 00:37:23,520
seen in other samples

1001
00:37:29,190 --> 00:37:26,240
one or more other less damaging impact

1002
00:37:30,950 --> 00:37:29,200
events may have affected the object or

1003
00:37:33,109 --> 00:37:30,960
the chelyabinsk material

1004
00:37:35,190 --> 00:37:33,119
more recently and there was a final

1005
00:37:36,630 --> 00:37:35,200
impact in space that occurred about 1.2

1006
00:37:38,790 --> 00:37:36,640
billion years ago

1007
00:37:41,349 --> 00:37:38,800
that kunin shizumi and colleagues at

1008
00:37:43,829 --> 00:37:41,359
berkeley detected uh and this event

1009
00:37:45,349 --> 00:37:43,839
exposed what became the surface of chely

1010
00:37:47,510 --> 00:37:45,359
events to space

1011
00:37:50,390 --> 00:37:47,520
that is the event that liberated the

1012
00:37:52,310 --> 00:37:50,400
object that we now know as chelly events

1013
00:37:55,670 --> 00:37:52,320
okay so let's now step through the

1014
00:37:58,230 --> 00:37:55,680
history of this object we begin

1015
00:37:59,910 --> 00:37:58,240
nearly 4.56 billion years ago with

1016
00:38:01,910 --> 00:37:59,920
formation of molten droplet chondrules

1017
00:38:03,589 --> 00:38:01,920
in the slower nebula and all of that

1018
00:38:06,710 --> 00:38:03,599
occurred within the first four million

1019
00:38:09,030 --> 00:38:06,720
years of solar system history okay

1020
00:38:12,069 --> 00:38:09,040
those chondrals and other dust particles

1021
00:38:14,310 --> 00:38:12,079
accreted to form a parent body the ll

1022
00:38:16,310 --> 00:38:14,320
chondrite parent body

1023
00:38:18,310 --> 00:38:16,320
and that material was thermally

1024
00:38:20,470 --> 00:38:18,320
metamorphosed over a period of about 10

1025
00:38:22,069 --> 00:38:20,480
million years now based on the thermal

1026
00:38:24,230 --> 00:38:22,079
metamorphic textures that we actually

1027
00:38:25,510 --> 00:38:24,240
see in the chelyabinsk meteorites we can

1028
00:38:27,270 --> 00:38:25,520
determine that the cellular grants

1029
00:38:29,750 --> 00:38:27,280
material used to be buried several

1030
00:38:30,790 --> 00:38:29,760
kilometers beneath the surface

1031
00:38:35,510 --> 00:38:30,800
okay

1032
00:38:40,470 --> 00:38:37,430
on the surface

1033
00:38:42,470 --> 00:38:40,480
about 115 million years ago and we know

1034
00:38:44,829 --> 00:38:42,480
that because of the analyses of the

1035
00:38:48,630 --> 00:38:44,839
shock blackened veins that cross cut the

1036
00:38:50,710 --> 00:38:48,640
sample analyses of other ll chondrites

1037
00:38:52,630 --> 00:38:50,720
that are associated with trojans

1038
00:38:55,109 --> 00:38:52,640
indicated that that parent body was then

1039
00:38:57,990 --> 00:38:55,119
hit severely by a large number of impact

1040
00:38:59,670 --> 00:38:58,000
events between about 4.3 and 3.8 billion

1041
00:39:01,349 --> 00:38:59,680
years ago

1042
00:39:02,790 --> 00:39:01,359
one or two impacts appear to have

1043
00:39:04,470 --> 00:39:02,800
slightly affected the chelyabinsk

1044
00:39:05,510 --> 00:39:04,480
material during the last 500 million

1045
00:39:07,349 --> 00:39:05,520
years

1046
00:39:09,990 --> 00:39:07,359
the meteoroid encountered a

1047
00:39:12,150 --> 00:39:10,000
gravitational resonance with jupiter

1048
00:39:14,069 --> 00:39:12,160
its orbit was modified and it became a

1049
00:39:15,910 --> 00:39:14,079
near-earth asteroid at that point and

1050
00:39:18,870 --> 00:39:15,920
the surface of the trojan benz meteoroid

1051
00:39:20,790 --> 00:39:18,880
is exposed to cosmic radiation about 1.2

1052
00:39:23,030 --> 00:39:20,800
years ago suggesting a collisional or

1053
00:39:25,670 --> 00:39:23,040
fragmentation event and then of course

1054
00:39:28,390 --> 00:39:25,680
in 2013 earlier this year

1055
00:39:30,150 --> 00:39:28,400
it had its final collision with planet

1056
00:39:32,310 --> 00:39:30,160
earth okay

1057
00:39:35,510 --> 00:39:32,320
that's fascinating our colleagues in

1058
00:39:38,470 --> 00:39:35,520
japan have actually visited a fragment

1059
00:39:40,470 --> 00:39:38,480
of the same l chondrite parent body it's

1060
00:39:42,310 --> 00:39:40,480
called asteroid itacawa

1061
00:39:44,710 --> 00:39:42,320
they sent the spacecraft hayabusa out

1062
00:39:46,550 --> 00:39:44,720
there they explored the asteroid they

1063
00:39:48,069 --> 00:39:46,560
touched down they collected a little bit

1064
00:39:50,870 --> 00:39:48,079
of that material and they returned it to

1065
00:39:53,270 --> 00:39:50,880
earth and so we can analyze it we know

1066
00:39:55,109 --> 00:39:53,280
it is composed of ll-chondrite material

1067
00:39:57,430 --> 00:39:55,119
so here's the asteroid for scale it's

1068
00:39:59,670 --> 00:39:57,440
540 meters across

1069
00:40:01,430 --> 00:39:59,680
for comparison there's the orion crew

1070
00:40:03,750 --> 00:40:01,440
vehicle that's going to carry uh

1071
00:40:06,470 --> 00:40:03,760
astronauts uh beyond low earth orbit the

1072
00:40:08,390 --> 00:40:06,480
moon asteroids and and potentially mars

1073
00:40:11,190 --> 00:40:08,400
uh and here's the current uh

1074
00:40:12,950 --> 00:40:11,200
international space station uh for scale

1075
00:40:16,470 --> 00:40:12,960
as well this is another view of the

1076
00:40:19,829 --> 00:40:16,480
asteroid it is a rocky body uh here for

1077
00:40:22,150 --> 00:40:19,839
scale is a boulder on the surface of

1078
00:40:25,270 --> 00:40:22,160
irokawa that is 20 meters in size that

1079
00:40:26,550 --> 00:40:25,280
is the size of the chelyabinsk meteoroid

1080
00:40:28,550 --> 00:40:26,560
what's a little bit frightening about

1081
00:40:31,430 --> 00:40:28,560
that is you suddenly realize

1082
00:40:33,990 --> 00:40:31,440
there are a lot of potential chelyabinsk

1083
00:40:35,510 --> 00:40:34,000
boulders out there

1084
00:40:40,550 --> 00:40:35,520
okay

1085
00:40:42,950 --> 00:40:40,560
that indicates that irakawa actually is

1086
00:40:44,710 --> 00:40:42,960
part of the inner asteroid belt uh

1087
00:40:46,950 --> 00:40:44,720
chelyabinsk is also part of the inner

1088
00:40:48,870 --> 00:40:46,960
asteroid belt although its orbit carried

1089
00:40:50,790 --> 00:40:48,880
it a little bit farther into the

1090
00:40:53,430 --> 00:40:50,800
asteroid belt

1091
00:40:55,990 --> 00:40:53,440
now here's a comparison of scale

1092
00:40:58,390 --> 00:40:56,000
i want to begin with a picture

1093
00:40:59,750 --> 00:40:58,400
of what the l chondrite parent body

1094
00:41:02,309 --> 00:40:59,760
looked like it was roughly 100

1095
00:41:05,109 --> 00:41:02,319
kilometers in diameter okay

1096
00:41:07,430 --> 00:41:05,119
for comparison there's asteroid in ocawa

1097
00:41:09,109 --> 00:41:07,440
and actually i've had to enlarge it by a

1098
00:41:10,390 --> 00:41:09,119
factor of eight simply so you could see

1099
00:41:12,390 --> 00:41:10,400
it

1100
00:41:14,550 --> 00:41:12,400
okay chili events you simply can't see

1101
00:41:15,750 --> 00:41:14,560
it's at 20 meters and this again drives

1102
00:41:17,190 --> 00:41:15,760
on the point that i mentioned just a

1103
00:41:20,390 --> 00:41:17,200
moment ago

1104
00:41:22,870 --> 00:41:20,400
this object has been fragmented it's

1105
00:41:25,510 --> 00:41:22,880
been scattered across space

1106
00:41:26,950 --> 00:41:25,520
producing a lot more itakawas and

1107
00:41:29,030 --> 00:41:26,960
chelyabinsk some of which could

1108
00:41:31,109 --> 00:41:29,040
potentially hurt earth in the future

1109
00:41:33,109 --> 00:41:31,119
okay now i want to say a couple of other

1110
00:41:34,390 --> 00:41:33,119
things quickly my mind is over there

1111
00:41:35,510 --> 00:41:34,400
telling me you're starting to run out of

1112
00:41:37,030 --> 00:41:35,520
time

1113
00:41:38,790 --> 00:41:37,040
so but these are these are important

1114
00:41:41,190 --> 00:41:38,800
things to understand if you're trying to

1115
00:41:43,270 --> 00:41:41,200
understand the hazards of future impact

1116
00:41:45,270 --> 00:41:43,280
events the first thing i need to explain

1117
00:41:47,109 --> 00:41:45,280
is i made this point before that the

1118
00:41:49,270 --> 00:41:47,119
object that produced ferringer or meteor

1119
00:41:50,150 --> 00:41:49,280
crater in arizona is

1120
00:41:51,829 --> 00:41:50,160
very

1121
00:41:54,870 --> 00:41:51,839
roughly the size of the chelyabinsk

1122
00:41:57,349 --> 00:41:54,880
object okay now a lot of newspapers and

1123
00:41:58,950 --> 00:41:57,359
and pundits and whatnot said oh

1124
00:42:00,309 --> 00:41:58,960
julia bence was half the size of some of

1125
00:42:02,309 --> 00:42:00,319
these other events that were explosive

1126
00:42:04,309 --> 00:42:02,319
okay so let's actually explore what that

1127
00:42:06,069 --> 00:42:04,319
means half the size are twice the size

1128
00:42:09,190 --> 00:42:06,079
so here's here's a picture a stony

1129
00:42:11,670 --> 00:42:09,200
asteroid 20 meters in diameter okay

1130
00:42:12,630 --> 00:42:11,680
here is an object two times larger

1131
00:42:15,990 --> 00:42:12,640
okay

1132
00:42:18,710 --> 00:42:16,000
40 meters in diameter

1133
00:42:20,069 --> 00:42:18,720
although it is two times larger in

1134
00:42:22,069 --> 00:42:20,079
diameter

1135
00:42:24,309 --> 00:42:22,079
it has eight times the volume and eight

1136
00:42:27,030 --> 00:42:24,319
times the mass if the density is the

1137
00:42:28,309 --> 00:42:27,040
same okay so is it two times or eight

1138
00:42:31,510 --> 00:42:28,319
times bigger

1139
00:42:33,910 --> 00:42:31,520
okay now let's put another twist on that

1140
00:42:36,630 --> 00:42:33,920
those are stony asteroids what happens

1141
00:42:39,670 --> 00:42:36,640
if we're looking at an iron asteroid

1142
00:42:41,589 --> 00:42:39,680
an iron asteroid also two times larger

1143
00:42:43,589 --> 00:42:41,599
has a higher density it might have a

1144
00:42:45,750 --> 00:42:43,599
density of seven grams per cubic

1145
00:42:49,829 --> 00:42:45,760
centimeter as opposed to two grams per

1146
00:42:52,069 --> 00:42:49,839
cubic centimeter so it is twice as large

1147
00:42:55,190 --> 00:42:52,079
with eight times the volume but it has

1148
00:42:57,750 --> 00:42:55,200
28 times the mass okay

1149
00:43:00,069 --> 00:42:57,760
now kinetic energy that is the explosive

1150
00:43:02,470 --> 00:43:00,079
nature of these types of impact events

1151
00:43:04,710 --> 00:43:02,480
is one half mv squared one half mass

1152
00:43:08,309 --> 00:43:04,720
times velocity square okay so

1153
00:43:11,349 --> 00:43:08,319
chelyabinsk is a 500 kiloton blast

1154
00:43:13,589 --> 00:43:11,359
an object with 28 times the mass has 28

1155
00:43:16,150 --> 00:43:13,599
times kinetic energy and would produce a

1156
00:43:17,990 --> 00:43:16,160
14 megaton blast that's about what

1157
00:43:20,630 --> 00:43:18,000
produced media crater in northern

1158
00:43:22,390 --> 00:43:20,640
arizona so something two times larger

1159
00:43:26,150 --> 00:43:22,400
can actually be

1160
00:43:28,710 --> 00:43:26,160
quite a bit more destructive now

1161
00:43:31,670 --> 00:43:28,720
during the worst um

1162
00:43:34,150 --> 00:43:31,680
our community and others at nasa and

1163
00:43:35,829 --> 00:43:34,160
fema and the organizers of the planetary

1164
00:43:37,910 --> 00:43:35,839
defense conference says what if

1165
00:43:39,829 --> 00:43:37,920
something like this were to truly

1166
00:43:41,910 --> 00:43:39,839
threaten the earth in the future so we

1167
00:43:44,630 --> 00:43:41,920
ran an exercise earlier this year in

1168
00:43:47,589 --> 00:43:44,640
april david morrison i think was there

1169
00:43:49,750 --> 00:43:47,599
uh it's a fascinating exercise everybody

1170
00:43:52,069 --> 00:43:49,760
in the community was divided up into a

1171
00:43:54,150 --> 00:43:52,079
series of teams astronomers trying to

1172
00:43:57,030 --> 00:43:54,160
detect the orbit and and so on and so

1173
00:43:58,390 --> 00:43:57,040
forth uh trying to characterize an

1174
00:43:59,190 --> 00:43:58,400
asteroid that might be threatening the

1175
00:44:00,630 --> 00:43:59,200
earth

1176
00:44:02,150 --> 00:44:00,640
a group that looked at mitigation

1177
00:44:04,230 --> 00:44:02,160
techniques to try to get this thing away

1178
00:44:05,589 --> 00:44:04,240
from the earth before it hit there was a

1179
00:44:07,430 --> 00:44:05,599
team that tried to predict what the

1180
00:44:08,390 --> 00:44:07,440
impact events would be that was the team

1181
00:44:09,829 --> 00:44:08,400
that i led

1182
00:44:10,710 --> 00:44:09,839
and you can see that there are several

1183
00:44:12,470 --> 00:44:10,720
other

1184
00:44:13,349 --> 00:44:12,480
governmental

1185
00:44:16,470 --> 00:44:13,359
press

1186
00:44:19,670 --> 00:44:16,480
space agency and public teams that were

1187
00:44:20,790 --> 00:44:19,680
put in a room and tried to work out

1188
00:44:25,990 --> 00:44:20,800
what

1189
00:44:28,870 --> 00:44:26,000
if something was detected okay so in

1190
00:44:31,990 --> 00:44:28,880
this exercise a threat was detected

1191
00:44:36,390 --> 00:44:32,000
there was a hypothetical asteroid 2013

1192
00:44:38,309 --> 00:44:36,400
pdce discovered on april 16 2013

1193
00:44:40,790 --> 00:44:38,319
it appeared to be a threatening object

1194
00:44:44,550 --> 00:44:40,800
200 to 300 meters in diameter the

1195
00:44:48,309 --> 00:44:44,560
initial probability of impact was .08

1196
00:44:51,430 --> 00:44:48,319
percent in 2028 that is about 15 years

1197
00:44:53,670 --> 00:44:51,440
after discovery if it were to impact the

1198
00:44:55,349 --> 00:44:53,680
velocity was estimated to be 12.4

1199
00:45:00,309 --> 00:44:55,359
kilometers per second with an energy

1200
00:45:01,109 --> 00:45:00,319
equivalent of about 300 megatons of tnt

1201
00:45:03,750 --> 00:45:01,119
note

1202
00:45:06,470 --> 00:45:03,760
if the object passed through what

1203
00:45:09,750 --> 00:45:06,480
astronomers call a keyhole

1204
00:45:11,990 --> 00:45:09,760
the certainty of impact would have risen

1205
00:45:15,430 --> 00:45:12,000
rather dramatically and that event if it

1206
00:45:16,150 --> 00:45:15,440
were to occur would occur in 2023 okay

1207
00:45:18,069 --> 00:45:16,160
so

1208
00:45:19,589 --> 00:45:18,079
in this simulation

1209
00:45:21,190 --> 00:45:19,599
we're trying to track the orbit we're

1210
00:45:22,550 --> 00:45:21,200
trying to better characterize the object

1211
00:45:25,190 --> 00:45:22,560
we're trying to predict what it happens

1212
00:45:27,349 --> 00:45:25,200
and uh as of 2019

1213
00:45:29,430 --> 00:45:27,359
the possible impact points

1214
00:45:30,790 --> 00:45:29,440
calculated impact points lie along

1215
00:45:32,550 --> 00:45:30,800
what's called a risk corridor which you

1216
00:45:34,550 --> 00:45:32,560
can see in a red line crossing across

1217
00:45:36,390 --> 00:45:34,560
the globe the possible impact sites

1218
00:45:39,829 --> 00:45:36,400
include southeast asia the coastal

1219
00:45:42,710 --> 00:45:39,839
waters of china korea and japan siberia

1220
00:45:45,589 --> 00:45:42,720
and the arctic ocean as orbit is better

1221
00:45:48,630 --> 00:45:45,599
defined in 2019 the probability of

1222
00:45:51,030 --> 00:45:48,640
impact has risen to 28 percent now that

1223
00:45:52,950 --> 00:45:51,040
risk order goes around the world

1224
00:45:55,750 --> 00:45:52,960
and passes directly over london and

1225
00:45:57,109 --> 00:45:55,760
paris to rather populist points on the

1226
00:45:59,270 --> 00:45:57,119
earth before passing over the

1227
00:46:02,230 --> 00:45:59,280
mediterranean sea and northern africa

1228
00:46:04,950 --> 00:46:02,240
calculations of impact effect and all

1229
00:46:06,950 --> 00:46:04,960
those different terrains had to be made

1230
00:46:09,670 --> 00:46:06,960
to better inform emergency management in

1231
00:46:11,910 --> 00:46:09,680
the countries along that corridor some

1232
00:46:13,910 --> 00:46:11,920
people were panicking in the room other

1233
00:46:14,950 --> 00:46:13,920
people were taking advantage of the

1234
00:46:16,790 --> 00:46:14,960
panic

1235
00:46:20,230 --> 00:46:16,800
interesting

1236
00:46:21,670 --> 00:46:20,240
okay also as of 2019 several missions

1237
00:46:24,069 --> 00:46:21,680
had been launched to deflect the

1238
00:46:26,470 --> 00:46:24,079
asteroid and they had all failed

1239
00:46:28,550 --> 00:46:26,480
tensions and the exercise started to go

1240
00:46:30,470 --> 00:46:28,560
up there was urgent discussions of

1241
00:46:32,870 --> 00:46:30,480
nuclear weapons and last-ditch attempt

1242
00:46:33,910 --> 00:46:32,880
to destroy the asteroid interestingly

1243
00:46:35,510 --> 00:46:33,920
enough

1244
00:46:37,510 --> 00:46:35,520
some of the

1245
00:46:41,510 --> 00:46:37,520
countries represented in fact some of

1246
00:46:43,270 --> 00:46:41,520
the countries in the target zone

1247
00:46:44,790 --> 00:46:43,280
did not want to use nuclear weapons

1248
00:46:47,030 --> 00:46:44,800
because they were so philosophically

1249
00:46:50,230 --> 00:46:47,040
opposed

1250
00:46:53,109 --> 00:46:50,240
the crisis grows in 2022 the probability

1251
00:46:54,950 --> 00:46:53,119
of impact is now 100

1252
00:46:56,870 --> 00:46:54,960
so the question is simply a matter of

1253
00:46:58,710 --> 00:46:56,880
where it will occur as the orbit is

1254
00:47:00,309 --> 00:46:58,720
increasingly refined the risk corridor

1255
00:47:01,190 --> 00:47:00,319
shrinks

1256
00:47:03,190 --> 00:47:01,200
to

1257
00:47:04,950 --> 00:47:03,200
europe and northern africa the impact

1258
00:47:08,710 --> 00:47:04,960
will occur in the united kingdom france

1259
00:47:10,309 --> 00:47:08,720
the mediterranean sea or northern africa

1260
00:47:12,150 --> 00:47:10,319
and then these questions arise do you

1261
00:47:14,790 --> 00:47:12,160
evacuate people are nuclear power

1262
00:47:16,870 --> 00:47:14,800
stations shut down et cetera et cetera

1263
00:47:20,950 --> 00:47:16,880
okay

1264
00:47:23,109 --> 00:47:20,960
then impact occurred at 7 00 700 on 21

1265
00:47:24,390 --> 00:47:23,119
november 2029

1266
00:47:25,750 --> 00:47:24,400
at the impact

1267
00:47:27,829 --> 00:47:25,760
fortunately occurred in the

1268
00:47:29,670 --> 00:47:27,839
mediterranean sea nonetheless shockwaves

1269
00:47:32,069 --> 00:47:29,680
roll over the surface of southern france

1270
00:47:34,390 --> 00:47:32,079
tsunamis follow crashing onto shorelines

1271
00:47:36,549 --> 00:47:34,400
around the entire mediterranean region

1272
00:47:40,309 --> 00:47:36,559
etc there's in general tremendous

1273
00:47:42,230 --> 00:47:40,319
devastation and it is not a good day

1274
00:47:44,309 --> 00:47:42,240
we actually learned a lot in that

1275
00:47:47,990 --> 00:47:44,319
exercise and we all walked away with a

1276
00:47:50,230 --> 00:47:48,000
lot of tasks to do including those with

1277
00:47:51,510 --> 00:47:50,240
nasa and fema okay

1278
00:47:53,349 --> 00:47:51,520
now

1279
00:47:57,990 --> 00:47:53,359
it's important a final

1280
00:48:00,069 --> 00:47:58,000
close by uh looking at yes i know

1281
00:48:02,069 --> 00:48:00,079
running out of time

1282
00:48:04,150 --> 00:48:02,079
look at uh

1283
00:48:06,790 --> 00:48:04,160
the probability of these impact events

1284
00:48:08,870 --> 00:48:06,800
and how to prepare them in a blue line

1285
00:48:11,670 --> 00:48:08,880
here what i'm plotting here that i

1286
00:48:14,549 --> 00:48:11,680
actually should say al harris plotted

1287
00:48:17,349 --> 00:48:14,559
and is in an nrc document called

1288
00:48:19,910 --> 00:48:17,359
defending planet earth is the impact

1289
00:48:21,990 --> 00:48:19,920
interval of objects of different sizes

1290
00:48:23,910 --> 00:48:22,000
okay and as we've said before smaller

1291
00:48:24,950 --> 00:48:23,920
objects hit more frequently than bigger

1292
00:48:26,790 --> 00:48:24,960
objects

1293
00:48:29,270 --> 00:48:26,800
this blue line represents the event that

1294
00:48:31,030 --> 00:48:29,280
we just simulated or i showed you in

1295
00:48:33,430 --> 00:48:31,040
that simulation at the planetary defense

1296
00:48:35,109 --> 00:48:33,440
conference this red line represents

1297
00:48:37,349 --> 00:48:35,119
chelyabinsk can you see that a chili

1298
00:48:39,510 --> 00:48:37,359
event size event occurs on average once

1299
00:48:42,390 --> 00:48:39,520
per 10 to 100 years okay and i've said

1300
00:48:44,790 --> 00:48:42,400
that several times on average okay that

1301
00:48:46,870 --> 00:48:44,800
is the average cadence but until we've

1302
00:48:48,950 --> 00:48:46,880
detected all objects any of these

1303
00:48:50,390 --> 00:48:48,960
objects including a mass extinction

1304
00:48:52,790 --> 00:48:50,400
hypoth

1305
00:48:56,230 --> 00:48:52,800
event could occur tomorrow okay so it's

1306
00:48:58,710 --> 00:48:56,240
something important to keep in mind okay

1307
00:49:00,390 --> 00:48:58,720
so how do we move forward

1308
00:49:02,309 --> 00:49:00,400
to move forward i want to actually draw

1309
00:49:04,630 --> 00:49:02,319
your attention to this diagram which is

1310
00:49:07,349 --> 00:49:04,640
similar you'll see that same curve

1311
00:49:10,390 --> 00:49:07,359
i've put the impact interval in years

1312
00:49:12,470 --> 00:49:10,400
from this axis to this axis and now over

1313
00:49:13,750 --> 00:49:12,480
here are the number of objects

1314
00:49:15,030 --> 00:49:13,760
explicitly

1315
00:49:16,470 --> 00:49:15,040
indicated

1316
00:49:18,710 --> 00:49:16,480
and there's this red curve that al

1317
00:49:19,430 --> 00:49:18,720
harris has put on this diagram that is

1318
00:49:21,430 --> 00:49:19,440
the

1319
00:49:23,750 --> 00:49:21,440
curve illustrating what has been

1320
00:49:25,670 --> 00:49:23,760
discovered at least as of 2009 and you

1321
00:49:26,549 --> 00:49:25,680
can see that there is a big gap

1322
00:49:28,950 --> 00:49:26,559
okay

1323
00:49:30,710 --> 00:49:28,960
so what do we need to do to address

1324
00:49:32,470 --> 00:49:30,720
future hazards the first thing that i

1325
00:49:34,470 --> 00:49:32,480
think we need to do is we need to have

1326
00:49:36,710 --> 00:49:34,480
an environmental assessment of events

1327
00:49:38,710 --> 00:49:36,720
that occurred in the geologic past

1328
00:49:40,309 --> 00:49:38,720
so that we have a foundation to estimate

1329
00:49:42,230 --> 00:49:40,319
future events those events should

1330
00:49:43,990 --> 00:49:42,240
include all cratering events and those

1331
00:49:46,470 --> 00:49:44,000
air bursts that produce meteoritic and

1332
00:49:50,069 --> 00:49:46,480
or geologic relics like meteor crater

1333
00:49:52,069 --> 00:49:50,079
impacted into northern arizona okay

1334
00:49:54,069 --> 00:49:52,079
simultaneously we need to have survey

1335
00:49:55,910 --> 00:49:54,079
programs that are designed to identify

1336
00:49:58,710 --> 00:49:55,920
potentially threatening objects and here

1337
00:50:01,109 --> 00:49:58,720
i'm pointing to this big detection gap

1338
00:50:04,150 --> 00:50:01,119
we don't have a very good understanding

1339
00:50:06,150 --> 00:50:04,160
of the objects of that size domain and

1340
00:50:08,630 --> 00:50:06,160
here's a little factoid of the 20

1341
00:50:11,990 --> 00:50:08,640
million objects the size of chelyabinsk

1342
00:50:13,750 --> 00:50:12,000
only 500 have been detected so far

1343
00:50:15,349 --> 00:50:13,760
finally mitigation concepts should be

1344
00:50:17,190 --> 00:50:15,359
developed that can be implemented to

1345
00:50:19,589 --> 00:50:17,200
reduce or completely resolve the hazard

1346
00:50:21,829 --> 00:50:19,599
near earth object any near-earth object

1347
00:50:24,230 --> 00:50:21,839
may pose for earth and it's important to

1348
00:50:26,470 --> 00:50:24,240
understand that the earlier we detect an

1349
00:50:28,710 --> 00:50:26,480
object that may hit the earth the easier

1350
00:50:29,829 --> 00:50:28,720
it will be to prevent the impact

1351
00:50:40,950 --> 00:50:29,839
okay

1352
00:50:44,470 --> 00:50:42,710
and then if you folks want to just come

1353
00:50:46,870 --> 00:50:44,480
to one of those two microphones

1354
00:50:49,190 --> 00:50:46,880
you'll hear it in there okay

1355
00:50:50,630 --> 00:50:49,200
so we're gonna just real quick to

1356
00:50:52,150 --> 00:50:50,640
mention we'll we'll take two questions

1357
00:50:53,670 --> 00:50:52,160
in here and then go to our overflow and

1358
00:50:55,109 --> 00:50:53,680
see if they have any and please wait if

1359
00:50:57,109 --> 00:50:55,119
we bring the mic to you so we make sure

1360
00:50:59,670 --> 00:50:57,119
it gets picked up on the cameras

1361
00:51:02,390 --> 00:50:59,680
just a separate question the composition

1362
00:51:08,150 --> 00:51:02,400
the composition of the contract

1363
00:51:12,470 --> 00:51:09,990
okay so yeah so let me repeat the

1364
00:51:13,829 --> 00:51:12,480
question the question is uh what can we

1365
00:51:16,309 --> 00:51:13,839
say about the composition of the

1366
00:51:18,069 --> 00:51:16,319
chondrite or the the impacting object

1367
00:51:20,710 --> 00:51:18,079
how is it compared to the earth okay the

1368
00:51:22,870 --> 00:51:20,720
first order chondritic meteorites

1369
00:51:24,069 --> 00:51:22,880
although they have subtle variations in

1370
00:51:26,150 --> 00:51:24,079
chemistry

1371
00:51:28,950 --> 00:51:26,160
have the composition of the sun minus

1372
00:51:31,349 --> 00:51:28,960
the gases hydrogen and helium okay and

1373
00:51:32,790 --> 00:51:31,359
the first order all of the planets earth

1374
00:51:35,270 --> 00:51:32,800
included accreted from that same

1375
00:51:38,150 --> 00:51:35,280
contradictive debris so

1376
00:51:39,990 --> 00:51:38,160
uh they have a lot of similarities that

1377
00:51:42,870 --> 00:51:40,000
is chelyabins has a lot of similarities

1378
00:51:44,549 --> 00:51:42,880
to both the sun and the earth now i

1379
00:51:46,790 --> 00:51:44,559
don't want to imply with that very

1380
00:51:49,109 --> 00:51:46,800
simple answer that the planets all have

1381
00:51:51,030 --> 00:51:49,119
the same composition and that's actually

1382
00:51:53,190 --> 00:51:51,040
interesting when we do compare the

1383
00:51:55,589 --> 00:51:53,200
composition of the earth mars venus and

1384
00:51:57,670 --> 00:51:55,599
so on they should have

1385
00:51:59,589 --> 00:51:57,680
started out accreting the same material

1386
00:52:01,670 --> 00:51:59,599
and have the same composition and when

1387
00:52:03,750 --> 00:52:01,680
we find they don't like earth and mars

1388
00:52:05,750 --> 00:52:03,760
are a little bit distinct that's a clue

1389
00:52:07,589 --> 00:52:05,760
that something else interesting is going

1390
00:52:09,030 --> 00:52:07,599
on and that's what the planetary science

1391
00:52:13,270 --> 00:52:09,040
community is spending a lot of time

1392
00:52:13,280 --> 00:52:16,829
does anyone here have a

1393
00:52:20,950 --> 00:52:19,349
question david can you can you comment

1394
00:52:22,710 --> 00:52:20,960
on the fact that the chelyabinsk

1395
00:52:24,710 --> 00:52:22,720
meteorite came in

1396
00:52:26,069 --> 00:52:24,720
at a very shallow angle and could just

1397
00:52:28,630 --> 00:52:26,079
have well come in

1398
00:52:29,829 --> 00:52:28,640
vertically over a city in terms of how

1399
00:52:32,150 --> 00:52:29,839
the

1400
00:52:34,390 --> 00:52:32,160
damage to a city within it coming

1401
00:52:36,630 --> 00:52:34,400
straight down yeah

1402
00:52:39,030 --> 00:52:36,640
i showed that plot of the chelyabinsk

1403
00:52:40,870 --> 00:52:39,040
trajectory and several other

1404
00:52:42,470 --> 00:52:40,880
recent

1405
00:52:43,910 --> 00:52:42,480
bolite events in the earth's atmosphere

1406
00:52:44,710 --> 00:52:43,920
and you saw it had a relatively shallow

1407
00:52:48,309 --> 00:52:44,720
angle

1408
00:52:50,710 --> 00:52:48,319
if the object had come in steeper it

1409
00:52:53,109 --> 00:52:50,720
would have deposited more of that energy

1410
00:52:55,349 --> 00:52:53,119
at the earth's surface based on computer

1411
00:52:59,349 --> 00:52:55,359
simulations many of those are done by

1412
00:53:01,589 --> 00:52:59,359
mark boslow in new mexico at los alamos

1413
00:53:03,670 --> 00:53:01,599
and therefore it could have been more

1414
00:53:06,309 --> 00:53:03,680
destructive yeah so the impact

1415
00:53:09,349 --> 00:53:06,319
trajectory actually has a bearing on the

1416
00:53:10,950 --> 00:53:09,359
consequences of the impact event

1417
00:53:13,030 --> 00:53:10,960
do we have any questions in the overflow

1418
00:53:21,109 --> 00:53:13,040
room not at this time

1419
00:53:26,710 --> 00:53:23,349
when you when you said that 20 million

1420
00:53:28,950 --> 00:53:26,720
uh chubby bee and size objects is that

1421
00:53:30,950 --> 00:53:28,960
all among all asteroids are among near

1422
00:53:40,309 --> 00:53:30,960
earth asteroids

1423
00:53:44,950 --> 00:53:42,390
the early photos of the damage showed

1424
00:53:47,510 --> 00:53:44,960
factory walls being knocked down

1425
00:53:49,270 --> 00:53:47,520
as a simple fix

1426
00:53:52,790 --> 00:53:49,280
could building codes

1427
00:53:54,829 --> 00:53:52,800
be improved and help reduce the damage

1428
00:53:57,990 --> 00:53:54,839
yes and i would say that

1429
00:54:00,470 --> 00:53:58,000
buildings in earthquake zones

1430
00:54:03,030 --> 00:54:00,480
would fare better from this type of

1431
00:54:04,230 --> 00:54:03,040
impact event than in areas that don't

1432
00:54:05,829 --> 00:54:04,240
have

1433
00:54:08,230 --> 00:54:05,839
those enhanced

1434
00:54:09,270 --> 00:54:08,240
construction

1435
00:54:13,030 --> 00:54:09,280
techniques

1436
00:54:13,040 --> 00:54:17,589
yes

1437
00:54:20,950 --> 00:54:19,190
how did you figure out the history of

1438
00:54:22,630 --> 00:54:20,960
this thing by just by just looking at

1439
00:54:24,309 --> 00:54:22,640
those grooves and things on there that

1440
00:54:26,710 --> 00:54:24,319
was amazing that you figured out that

1441
00:54:28,309 --> 00:54:26,720
much detail how did you do that

1442
00:54:30,230 --> 00:54:28,319
well

1443
00:54:32,630 --> 00:54:30,240
that's what cosmo chemists do that's

1444
00:54:34,150 --> 00:54:32,640
what the meteoritical community does

1445
00:54:35,750 --> 00:54:34,160
um i mean

1446
00:54:37,349 --> 00:54:35,760
and and i know that's kind of a glib

1447
00:54:40,789 --> 00:54:37,359
answer but literally that's what we've

1448
00:54:42,069 --> 00:54:40,799
been doing for over 100 years

1449
00:54:50,829 --> 00:54:42,079
the

1450
00:54:53,589 --> 00:54:50,839
that allows us to identify which

1451
00:54:56,150 --> 00:54:53,599
meteorites can be grouped together which

1452
00:54:58,870 --> 00:54:56,160
meteorites came from the same parent

1453
00:55:01,270 --> 00:54:58,880
body in the asteroid belt and in fact

1454
00:55:03,670 --> 00:55:01,280
based on the collection of meteorites

1455
00:55:06,230 --> 00:55:03,680
that we have it appears that there were

1456
00:55:08,710 --> 00:55:06,240
in excess of 100 small planets that

1457
00:55:09,750 --> 00:55:08,720
survive between the orbits of mars and

1458
00:55:11,510 --> 00:55:09,760
jupiter

1459
00:55:13,589 --> 00:55:11,520
and there's some ideas as to why they

1460
00:55:15,430 --> 00:55:13,599
didn't accrete to mars

1461
00:55:17,270 --> 00:55:15,440
or some of the other planets and in fact

1462
00:55:19,190 --> 00:55:17,280
it may have everything to do with the

1463
00:55:21,670 --> 00:55:19,200
gravitational influence of jupiter which

1464
00:55:23,270 --> 00:55:21,680
didn't allow that that to occur but it's

1465
00:55:25,430 --> 00:55:23,280
based on the mineralogy and the

1466
00:55:28,309 --> 00:55:25,440
chemistry of these objects now

1467
00:55:30,549 --> 00:55:28,319
the other part of the story that i told

1468
00:55:31,349 --> 00:55:30,559
you had something to do

1469
00:55:33,510 --> 00:55:31,359
with

1470
00:55:36,150 --> 00:55:33,520
how deep it was buried

1471
00:55:38,470 --> 00:55:36,160
we can determine that because the the

1472
00:55:41,109 --> 00:55:38,480
deeper the object was buried the hotter

1473
00:55:43,910 --> 00:55:41,119
it got and the slower it cooled

1474
00:55:45,430 --> 00:55:43,920
so that can be equated to a depth

1475
00:55:47,670 --> 00:55:45,440
and then we

1476
00:55:49,829 --> 00:55:47,680
outlined some of the collisional history

1477
00:55:52,630 --> 00:55:49,839
of the object and we're able to

1478
00:55:56,069 --> 00:55:52,640
determine that because if there is a

1479
00:55:59,109 --> 00:55:56,079
impact event with sufficient energy

1480
00:56:00,150 --> 00:55:59,119
it will reset the radiometric clocks in

1481
00:56:02,390 --> 00:56:00,160
the rock

1482
00:56:04,710 --> 00:56:02,400
and so we can determine the age

1483
00:56:09,349 --> 00:56:04,720
of the new impact rock and then put that

1484
00:56:11,829 --> 00:56:10,630
okay go ahead

1485
00:56:17,109 --> 00:56:11,839
we do have a

1486
00:56:22,069 --> 00:56:19,750
yeah i was interested in the um

1487
00:56:24,870 --> 00:56:22,079
basically the frequency

1488
00:56:27,670 --> 00:56:24,880
that objects actually survive

1489
00:56:28,549 --> 00:56:27,680
to impact the surface of the earth

1490
00:56:30,950 --> 00:56:28,559
so

1491
00:56:33,750 --> 00:56:30,960
say in the last 100 years

1492
00:56:35,589 --> 00:56:33,760
what would be an average value for the

1493
00:56:37,910 --> 00:56:35,599
number of impacts and whether or not

1494
00:56:39,829 --> 00:56:37,920
that's changed

1495
00:56:42,230 --> 00:56:39,839
substantially over

1496
00:56:43,270 --> 00:56:42,240
you know the past that we know of

1497
00:56:45,510 --> 00:56:43,280
okay

1498
00:56:48,710 --> 00:56:45,520
um well it

1499
00:56:50,789 --> 00:56:48,720
again the smaller impacting objects

1500
00:56:51,670 --> 00:56:50,799
occur far more frequently than the small

1501
00:56:53,829 --> 00:56:51,680
one

1502
00:56:56,150 --> 00:56:53,839
and in fact small meteorite producing

1503
00:56:58,390 --> 00:56:56,160
impact events are pretty darn common

1504
00:57:00,230 --> 00:56:58,400
i've not done this calculation for texas

1505
00:57:02,549 --> 00:57:00,240
and now that i live here i should

1506
00:57:04,150 --> 00:57:02,559
but in venera arizona where i spent most

1507
00:57:06,069 --> 00:57:04,160
of my life

1508
00:57:08,789 --> 00:57:06,079
the answer was two to three fist-sized

1509
00:57:09,910 --> 00:57:08,799
meteorites fell in arizona every year

1510
00:57:12,870 --> 00:57:09,920
okay

1511
00:57:15,910 --> 00:57:12,880
now larger objects the size of

1512
00:57:17,750 --> 00:57:15,920
chelyabinsk um they seem to be hitting

1513
00:57:20,470 --> 00:57:17,760
the atmosphere somewhere between 10 and

1514
00:57:22,710 --> 00:57:20,480
100 years and i have to say we can't be

1515
00:57:24,789 --> 00:57:22,720
more precise for a couple of reasons one

1516
00:57:27,430 --> 00:57:24,799
we don't have a lot of data

1517
00:57:29,349 --> 00:57:27,440
and two that actually can vary quite a

1518
00:57:31,190 --> 00:57:29,359
lot even if we did have a lot of data in

1519
00:57:33,270 --> 00:57:31,200
fact i was discussing this very same

1520
00:57:35,109 --> 00:57:33,280
issue with david morrison one of our

1521
00:57:37,270 --> 00:57:35,119
country's most esteemed astronomers just

1522
00:57:39,510 --> 00:57:37,280
before the talk uh some of our

1523
00:57:40,870 --> 00:57:39,520
colleagues will say it's a firm 20 20 to

1524
00:57:43,190 --> 00:57:40,880
30 years

1525
00:57:44,789 --> 00:57:43,200
some of us think it's more like 50 67

1526
00:57:46,230 --> 00:57:44,799
years but it could be a little bit

1527
00:57:47,589 --> 00:57:46,240
longer so there's there is some

1528
00:57:49,030 --> 00:57:47,599
uncertainty

1529
00:57:51,109 --> 00:57:49,040
to the answer that i can give you to

1530
00:57:53,910 --> 00:57:51,119
that question now the other part of that

1531
00:57:56,470 --> 00:57:53,920
question is how often these things

1532
00:57:58,230 --> 00:57:56,480
either cause damage or reach the ground

1533
00:57:59,510 --> 00:57:58,240
and there it's very important to

1534
00:58:01,670 --> 00:57:59,520
understand

1535
00:58:04,390 --> 00:58:01,680
that the size of the object and the

1536
00:58:05,990 --> 00:58:04,400
strength of the object is very important

1537
00:58:08,950 --> 00:58:06,000
when we're talking about these small

1538
00:58:11,030 --> 00:58:08,960
objects okay when we when we talk about

1539
00:58:13,109 --> 00:58:11,040
something that is mountainous in size

1540
00:58:14,870 --> 00:58:13,119
like like the 10 kilometer object that

1541
00:58:17,430 --> 00:58:14,880
produced the chick's loop crater that

1542
00:58:18,789 --> 00:58:17,440
wiped out dinosaurs okay that object was

1543
00:58:21,190 --> 00:58:18,799
so big

1544
00:58:24,150 --> 00:58:21,200
it would it didn't see the atmosphere it

1545
00:58:26,069 --> 00:58:24,160
just went it's so massive okay but

1546
00:58:27,589 --> 00:58:26,079
smaller objects

1547
00:58:30,230 --> 00:58:27,599
that are

1548
00:58:31,990 --> 00:58:30,240
both small and weak can catastrophically

1549
00:58:34,390 --> 00:58:32,000
fragment

1550
00:58:36,470 --> 00:58:34,400
stones stony asteroids are much weaker

1551
00:58:38,870 --> 00:58:36,480
than iron asteroids and so they tend to

1552
00:58:41,430 --> 00:58:38,880
fragment in the atmosphere more often

1553
00:58:44,349 --> 00:58:41,440
and in fact if you look at the earth's

1554
00:58:47,109 --> 00:58:44,359
smallest craters they are almost

1555
00:58:49,109 --> 00:58:47,119
exclusively produced by iron asteroids

1556
00:58:51,349 --> 00:58:49,119
and that is because the small iron

1557
00:58:53,910 --> 00:58:51,359
asteroids can reach the surface while

1558
00:58:57,829 --> 00:58:53,920
the smaller stony asteroids are unable

1559
00:59:01,750 --> 00:58:57,839
to and so they burst in the atmosphere

1560
00:59:05,990 --> 00:59:03,349
not at this time thank you hey we'll

1561
00:59:09,349 --> 00:59:06,000
take two more in here

1562
00:59:13,109 --> 00:59:09,359
um i heard that uh the uh i don't know

1563
00:59:16,950 --> 00:59:15,510
military have been monitoring

1564
00:59:18,390 --> 00:59:16,960
things coming through the atmosphere and

1565
00:59:20,950 --> 00:59:18,400
they have

1566
00:59:23,349 --> 00:59:20,960
data that they were discussing

1567
00:59:24,789 --> 00:59:23,359
releasing to astronomers to help provide

1568
00:59:27,829 --> 00:59:24,799
more data do you know anything about

1569
00:59:29,750 --> 00:59:27,839
that yes uh the us government uh we

1570
00:59:32,150 --> 00:59:29,760
refer to that as simply us government

1571
00:59:34,069 --> 00:59:32,160
sensors we don't talk too much about the

1572
00:59:35,430 --> 00:59:34,079
way in which they do this

1573
00:59:37,430 --> 00:59:35,440
i mean obviously those of us in the

1574
00:59:40,230 --> 00:59:37,440
business understand that but the us

1575
00:59:42,789 --> 00:59:40,240
government was very forthcoming uh they

1576
00:59:45,270 --> 00:59:42,799
turned over that data and the estimate

1577
00:59:47,270 --> 00:59:45,280
of 500 kilotons explosive energy is

1578
00:59:48,390 --> 00:59:47,280
consistent with the us government sensor

1579
00:59:49,109 --> 00:59:48,400
data

1580
00:59:51,109 --> 00:59:49,119
now

1581
00:59:53,349 --> 00:59:51,119
the energy can be

1582
00:59:54,549 --> 00:59:53,359
estimated by several other techniques

1583
00:59:56,789 --> 00:59:54,559
one of which

1584
00:59:57,990 --> 00:59:56,799
interestingly enough is a seismic

1585
01:00:00,549 --> 00:59:58,000
technique

1586
01:00:03,829 --> 01:00:00,559
that the world deployed as a

1587
01:00:06,710 --> 01:00:03,839
counter-measure to nuclear weapons tests

1588
01:00:09,349 --> 01:00:06,720
okay so this is deployed nationally

1589
01:00:10,870 --> 01:00:09,359
so that if a country does

1590
01:00:12,630 --> 01:00:10,880
detonate against

1591
01:00:15,190 --> 01:00:12,640
trees and agreements a nuclear weapon

1592
01:00:17,430 --> 01:00:15,200
that will be detected and so that

1593
01:00:31,990 --> 01:00:17,440
system was also employed in determining

1594
01:00:38,069 --> 01:00:35,109
most of the meteorites or asteroids that

1595
01:00:40,829 --> 01:00:38,079
become meteorites it impact the earth

1596
01:00:45,030 --> 01:00:44,150
lectures gave the asteroid belt as the

1597
01:00:47,270 --> 01:00:45,040
main

1598
01:00:51,190 --> 01:00:47,280
source of these come these

1599
01:00:53,829 --> 01:00:51,200
meteorites that we have

1600
01:00:56,630 --> 01:00:53,839
then we hear i hear about

1601
01:00:59,470 --> 01:00:56,640
meteorites from mars that are found in

1602
01:01:01,109 --> 01:00:59,480
antarctica are of a different com

1603
01:01:02,230 --> 01:01:01,119
comprehension

1604
01:01:03,430 --> 01:01:02,240
how does

1605
01:01:05,589 --> 01:01:03,440
mars

1606
01:01:08,470 --> 01:01:05,599
when when did those meteorites come from

1607
01:01:10,230 --> 01:01:08,480
mars and how do we know the difference

1608
01:01:11,829 --> 01:01:10,240
between those and the ones from the

1609
01:01:13,349 --> 01:01:11,839
asteroid belt yeah that's a great

1610
01:01:15,430 --> 01:01:13,359
question

1611
01:01:17,270 --> 01:01:15,440
meteorites from mars and for that matter

1612
01:01:19,109 --> 01:01:17,280
meteorites from the moon fascinate

1613
01:01:20,710 --> 01:01:19,119
people in meteorated community because

1614
01:01:23,750 --> 01:01:20,720
they are in some sense free sample

1615
01:01:25,990 --> 01:01:23,760
return missions okay and what

1616
01:01:28,549 --> 01:01:26,000
what has happened in those cases is

1617
01:01:30,789 --> 01:01:28,559
asteroids have hit the surface of mars

1618
01:01:33,349 --> 01:01:30,799
and hit the surface of the moon and some

1619
01:01:35,109 --> 01:01:33,359
of the material that's ejected in those

1620
01:01:37,990 --> 01:01:35,119
events that in the crater forming

1621
01:01:39,430 --> 01:01:38,000
process actually leave with velocities

1622
01:01:41,910 --> 01:01:39,440
that allow them to escape those

1623
01:01:43,829 --> 01:01:41,920
planetary gravities okay then they get

1624
01:01:45,270 --> 01:01:43,839
into space and some of that debris it's

1625
01:01:46,789 --> 01:01:45,280
a small proportion that some of that

1626
01:01:48,549 --> 01:01:46,799
debris will collide with the other

1627
01:01:50,150 --> 01:01:48,559
planets like the earth

1628
01:01:51,589 --> 01:01:50,160
and so we do have a wonderful collection

1629
01:01:53,109 --> 01:01:51,599
of samples from mars and we have a

1630
01:01:54,630 --> 01:01:53,119
wonderful collection of samples from the

1631
01:01:55,349 --> 01:01:54,640
moon now

1632
01:01:56,950 --> 01:01:55,359
the

1633
01:01:59,589 --> 01:01:56,960
meteorites

1634
01:02:01,990 --> 01:01:59,599
that we understand today came from the

1635
01:02:04,309 --> 01:02:02,000
moon were not actually discovered or

1636
01:02:06,150 --> 01:02:04,319
recognized as being from the moon until

1637
01:02:07,270 --> 01:02:06,160
about a decade after the apollo program

1638
01:02:10,390 --> 01:02:07,280
shut down

1639
01:02:11,990 --> 01:02:10,400
but we in that case had all of these

1640
01:02:13,910 --> 01:02:12,000
wonderful samples that the astronauts

1641
01:02:15,430 --> 01:02:13,920
had collected brought down to earth we

1642
01:02:16,789 --> 01:02:15,440
identified their very distinctive

1643
01:02:18,230 --> 01:02:16,799
chemistry and then when we saw a

1644
01:02:19,990 --> 01:02:18,240
meteorite with the very same chemistry

1645
01:02:22,630 --> 01:02:20,000
we said aha we know where those come

1646
01:02:25,029 --> 01:02:22,640
from now the ones on mars

1647
01:02:26,870 --> 01:02:25,039
that was a little trickier puzzle

1648
01:02:29,349 --> 01:02:26,880
because of course we've not yet sent a

1649
01:02:30,390 --> 01:02:29,359
crew nor even a robotic sample return

1650
01:02:32,230 --> 01:02:30,400
mission

1651
01:02:34,870 --> 01:02:32,240
to to mars

1652
01:02:38,230 --> 01:02:34,880
but in that case um

1653
01:02:41,430 --> 01:02:38,240
the atmosphere of mars had been measured

1654
01:02:43,910 --> 01:02:41,440
by landers like fighting okay

1655
01:02:46,710 --> 01:02:43,920
and then we got these samples back on

1656
01:02:48,549 --> 01:02:46,720
earth and some very smart people some of

1657
01:02:49,589 --> 01:02:48,559
them right here at the johnson space

1658
01:02:52,069 --> 01:02:49,599
center

1659
01:02:54,789 --> 01:02:52,079
analyze some shock melted material

1660
01:02:56,549 --> 01:02:54,799
within those meteorites and found that

1661
01:02:58,309 --> 01:02:56,559
some of the atmosphere on their host

1662
01:03:00,390 --> 01:02:58,319
planet was trapped

1663
01:03:02,470 --> 01:03:00,400
and the composition of that trap gas

1664
01:03:04,069 --> 01:03:02,480
turned out to be absolutely identical to

1665
01:03:05,430 --> 01:03:04,079
what was being measured on the surface

1666
01:03:07,589 --> 01:03:05,440
of mars

1667
01:03:09,190 --> 01:03:07,599
so that has now been bolstered by a lot

1668
01:03:11,109 --> 01:03:09,200
of other evidence but we're really

1669
01:03:13,430 --> 01:03:11,119
confident that we have a really handsome

1670
01:03:15,670 --> 01:03:13,440
collection of samples from mars

1671
01:03:18,950 --> 01:03:15,680
i have to say as interesting as those

1672
01:03:22,630 --> 01:03:18,960
are those is a very tiny proportion

1673
01:03:23,589 --> 01:03:22,640
of the meteorites that fall on earth

1674
01:03:24,950 --> 01:03:23,599
all right well let's take our speaker

1675
01:03:26,789 --> 01:03:24,960
one more time

1676
01:03:27,829 --> 01:03:26,799
and if you have another question

1677
01:03:37,829 --> 01:03:27,839
see if you can catch them now in the