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nasa's jet propulsion laboratory

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presents

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the von carmen lecture a series of talks

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by scientists and engineers who are

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exploring our planet our solar system

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good evening ladies and gentlemen how's

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well thank you very much for coming out

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uh it's nice and cool in here at least

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right

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so anyway shall we with thousands of

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planets now known around other stars

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it's natural to wonder why so many

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planetary systems are quite different

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from our own

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some stars have several planets inside

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the location of mercury's orbit where

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our solar system is basically empty

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while other stars have planets more

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massive than our jupiter on looping

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eccentric orbits a few stars have hot

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jupiters circling every few days on

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orbits so tight the starlight heats the

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planet's atmospheres beyond the point

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where iron vaporizes

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and many stars have planets intermediate

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in size between our rocky earth and icy

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uranus sizes that are completely missing

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from our solar system

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and some planets orbit not one but two

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stars

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so where did all this diversity come

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from we know planets must form from the

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dust and gas orbiting young stars

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because we see the orbiting material

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with the hubble and spitzer telescopes

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and ground-based telescopes

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but the dust makes the material opaque

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at optical and infrared wavelengths so

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it's hard to know what's going on inside

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in recent years our view has become

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clear enough to make out some features

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that might be caused by young planets

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orbiting within the material tonight's

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guest will discuss several of the new

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images and a few of the 3d computer

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models astronomers are using to try to

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learn how planets are born into such

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diversity

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tonight's guest grew up in australia

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where as a teenager he built a small

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telescope that he used to study the

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milky way and comets

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he earned a bachelor's degree at the

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university of sydney then moved to the

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u.s for a phd in astrophysics at uc

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santa cruz and after his stints at the

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university of maryland and uc santa

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barbara he came to jpl where he now

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supervises the interstellar and

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heliospheric physics group

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for him a typical workday involves

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building computer programs to compare

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models of what happens during planet

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formation with the observations sent

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back by space telescopes ladies and

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gentlemen please help me welcome

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hello and welcome

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i guess the mic is on

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uh so i would like to share with you the

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story of what we know so far about

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in the last 20 years thousands of

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planets have been discovered at an

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increasing rate

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only the few brightest

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are directly imaged like this one here

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so the star has been mostly removed in

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the center and then the three little

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dots b c and d are the three planets

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here but these are unusual they're uh

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particularly large and bright and

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particularly far from their star in most

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cases we cannot see these thousands of

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most were found by

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two methods

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either using the the motions of the

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stars in response to the planet so this

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movie shows a star here

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and a planet going around it and you can

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see that

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although the planet is going around the

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star the star is also in a sense going

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around the planet it moves a little in

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response to the planet's gravity

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and that means that the bright star we

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can we can just look at it and see its

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motion towards us and away from us

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and in the same way that when a fire

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engine comes toward you its pitch gets

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higher and then as it goes away the

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pitch gets lower same thing happens with

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the star's light so we can see a bluing

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as it comes towards us and a reddening

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as it goes away so we can use this

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radial velocity method that's been used

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to discover many of the new planets

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the other main way is through transits

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and that basically is just a fancy way

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of saying that the planet goes in front

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of the star and blocks out a little bit

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of its light

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so uh the biggest planet in our own

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solar system jupiter is about one-tenth

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as big across as the sun which means

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one-tenth in each direction means about

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1 100th total of the sun's light would

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be blocked if jupiter were to pass

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across its face as seen by

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somebody very far away

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and so

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many most of the planets that have been

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discovered have been found by this

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method using the kepler space telescope

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which studies a large number of stars

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looking for the slight dimming when a

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as better telescopes have been built and

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also as we've gotten better at analyzing

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the results from the telescopes are

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teasing out the little signals that we

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get from the planets

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the uh the masses of the planets that we

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can see have gone down so this shows

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years

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uh the the year in which each planet was

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discovered so the first one that

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everybody believed was about 1995 here

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and as a function of the of the the mass

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so jupiter is here neptune and the earth

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and you can see that as techniques have

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gotten better the the lowest mass that

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we can detect has gone down and down

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and now it's at about the mass of the

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earth so it's an exciting time

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to be part of this search for new

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by the way uh gray is the radial

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velocities and red is the transits and

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so you can see that when kepler the

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kepler telescope was launched into space

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in 2009 the red dots really take off so

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so many more planets have been

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it's also an exciting time because

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thousands more of the planets are going

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to be discovered in the next few years

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so a couple of years ago the european

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space agency launched gaia which

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measures the

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positions of the stars very accurately

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and so

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if the

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as the planet goes around once again you

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can see the stars motion but this time

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in the plane of the sky

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and so gaia should discover several

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thousand more new planets

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and also tess which is a super kepler um

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with an even bigger fly's eye of of

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telescopes with more megapixels and it

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will because it has that bigger field of

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view it can study nearby stars kepler

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had to concentrate on a smaller field uh

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far away but uh tess the transiting

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exoplanet survey satellite will be able

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to see

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all of the nearby stars by scanning the

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sky so we'll find out about our

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neighbours the planets around our

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neighbor stars

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and that's due to launch in a couple of

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so tonight i'd like to discuss three

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questions first

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um what are other stars

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planets like

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uh and like the other questions this is

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one that people have been asking for a

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long time and it's it's great that now

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we have a chance at last to answer it

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and i'd like to share what we know so

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far

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about the answer to this question

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and the second one is

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um how are they different from the

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planets around

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our own sun which we've known about for

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thousands of years and it turns out they

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are quite different many of them are

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totally unlike anything we've known up

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to now

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and then the third question is why are

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they different that is

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what's different about their history

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what's different about how they came to

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be where they are

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um that has made them so different from

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our own solar system and so diverse so

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different from one another

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so on to the first question

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so

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the first planets to be found were

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what are now called hot jupiters and

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they were first to be found because

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they're as big and as massive as jupiter

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you can see this one is

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a good fraction of the of the diameter

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of its host star here

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so big and heavy means that they make

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the star move a lot so that that

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movement is easy to see and the other

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thing is that they are very close to

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their star many of them are in orbits of

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just a few days instead of

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365 days like our earth

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and so they're whizzing around the star

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so often that you just need to look for

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a few days with a telescope and you'll

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see that signal repeat you'll see the

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star move towards you and then away from

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you and then towards again

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and so because of that quick repetition

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they are easy to see

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but because they are so close to their

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stars they become very hot they become

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much hotter than even the innermost

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planet in our solar system mercury

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and on their surface the temperature is

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hot enough to meet to melt most metals

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and so

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they they have to be gas giants even if

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some of the gas is

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metal vapor

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and

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based on the number of these that have

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been found

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uh they must orbit around one percent of

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the nearby sun-like stars so there are a

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lot of them but they're still

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but they are completely

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the next easiest kind of of new planets

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to find are the eccentric giants so

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these may have a mass close to that of

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jupiter but instead on instead of going

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on a nice steady circular orbit they

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they go on big loops they start they

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start out far from their star they

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plunge in very close and they go far out

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again this example goes well outside the

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orbit of mars

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if if you were to place it in our solar

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system and in just inside the orbit of

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mercury

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and

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the fact that they're eccentric means

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that they must have had something

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violent happen to them in the past to

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knock them off the orbit where they were

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initially formed

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and the number of these that have been

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found suggested they orbit around five

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percent of the nearby sun-like stars

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but then the third kind the hardest to

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find but the most numerous

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are smaller

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and uh they're on they're on orbits less

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than about 100 days because that's what

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kepler has been able to detect this

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each so each little

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set of circles is one of the planetary

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systems

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the colors just show the

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the order so red is nearest to the star

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yellow is next and so on

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and you can see the relative sizes so

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here's a super jupiter and there are

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many smaller planets

283
00:10:44,710 --> 00:10:42,399
and for comparison up here is our solar

284
00:10:45,670 --> 00:10:44,720
system with mercury venus the earth and

285
00:10:47,110 --> 00:10:45,680
mars

286
00:10:49,509 --> 00:10:47,120
we're going to zoom in because a lot of

287
00:10:51,509 --> 00:10:49,519
these systems are really small very

288
00:10:54,069 --> 00:10:51,519
compact you have in many cases several

289
00:10:56,310 --> 00:10:54,079
planets orbiting quite close to their

290
00:11:00,710 --> 00:10:56,320
star

291
00:11:04,710 --> 00:11:01,750
so

292
00:11:07,590 --> 00:11:04,720
but the bottom line from all of these

293
00:11:10,550 --> 00:11:07,600
uh three classes new classes of of

294
00:11:12,230 --> 00:11:10,560
planets is that if you look up at one of

295
00:11:14,870 --> 00:11:12,240
the bright stars in the sky bright means

296
00:11:17,030 --> 00:11:14,880
it's probably nearby there's about a 50

297
00:11:19,829 --> 00:11:17,040
percent chance that it has one or more

298
00:11:22,550 --> 00:11:19,839
planets earth mass or greater and these

299
00:11:24,389 --> 00:11:22,560
numbers are just because um

300
00:11:26,389 --> 00:11:24,399
this is what we are able to detect so

301
00:11:31,910 --> 00:11:26,399
far there could be more there could be

302
00:11:35,590 --> 00:11:33,350
so

303
00:11:37,030 --> 00:11:35,600
the the second question i'd like to talk

304
00:11:40,150 --> 00:11:37,040
about is

305
00:11:43,110 --> 00:11:40,160
uh how these planets are different

306
00:11:44,949 --> 00:11:43,120
from the planets in our own solar system

307
00:11:46,949 --> 00:11:44,959
and this is where it gets interesting

308
00:11:48,949 --> 00:11:46,959
because it starts to tie

309
00:11:51,509 --> 00:11:48,959
um the strangenesses of these new

310
00:11:58,150 --> 00:11:51,519
planets to how we perhaps came to be

311
00:12:04,949 --> 00:11:59,269
so

312
00:12:06,870 --> 00:12:04,959
is mercury and its orbit is 88 days long

313
00:12:09,430 --> 00:12:06,880
it's about four tenths

314
00:12:11,910 --> 00:12:09,440
as big across as the orbit of the earth

315
00:12:13,190 --> 00:12:11,920
compare that with this one system of

316
00:12:14,550 --> 00:12:13,200
planets around another star the

317
00:12:17,190 --> 00:12:14,560
kepler-11

318
00:12:20,150 --> 00:12:17,200
system and it has one two three four

319
00:12:22,069 --> 00:12:20,160
five planets inside mercury's orbit and

320
00:12:25,509 --> 00:12:22,079
then another one in between mercury and

321
00:12:27,590 --> 00:12:25,519
venus if you put it in our system

322
00:12:30,150 --> 00:12:27,600
so in our solar system this region

323
00:12:32,629 --> 00:12:30,160
inside here is empty

324
00:12:34,230 --> 00:12:32,639
but in the other system there are

325
00:12:36,150 --> 00:12:34,240
quite a number of planets and this has

326
00:12:37,990 --> 00:12:36,160
been repeated again and again

327
00:12:39,910 --> 00:12:38,000
it's a common pattern among the systems

328
00:12:42,069 --> 00:12:39,920
that we've been able to see

329
00:12:43,670 --> 00:12:42,079
so this is a great mystery why is our

330
00:12:45,350 --> 00:12:43,680
solar system

331
00:12:46,470 --> 00:12:45,360
so different from these other systems

332
00:12:49,269 --> 00:12:46,480
why is our

333
00:12:50,710 --> 00:12:49,279
solar system special in some way

334
00:12:52,870 --> 00:12:50,720
or rare

335
00:12:54,790 --> 00:12:52,880
in most other respects in terms of our

336
00:12:56,710 --> 00:12:54,800
place in the galaxy or our galaxy's

337
00:12:58,310 --> 00:12:56,720
place in the universe

338
00:13:00,949 --> 00:12:58,320
uh we are not special we are just

339
00:13:08,230 --> 00:13:00,959
typical but our solar system does seem

340
00:13:13,590 --> 00:13:10,389
in our solar system

341
00:13:14,949 --> 00:13:13,600
so here's everything to scale the sun

342
00:13:17,350 --> 00:13:14,959
here on the left

343
00:13:20,710 --> 00:13:17,360
we have two big planets jupiter and

344
00:13:22,550 --> 00:13:20,720
saturn both about 10 times the radius of

345
00:13:25,190 --> 00:13:22,560
the earth shown here

346
00:13:27,269 --> 00:13:25,200
we also have two ice giants ice and gas

347
00:13:28,949 --> 00:13:27,279
giants uranus and neptune which are each

348
00:13:30,949 --> 00:13:28,959
about four times

349
00:13:32,790 --> 00:13:30,959
the diameter of the earth then we have

350
00:13:35,030 --> 00:13:32,800
earth and venus which are pretty similar

351
00:13:36,069 --> 00:13:35,040
except that venus is has serious

352
00:13:37,990 --> 00:13:36,079
greenhouse

353
00:13:43,910 --> 00:13:38,000
effect and then some smaller stuff

354
00:13:47,590 --> 00:13:46,389
in contrast around the stars that we've

355
00:13:51,829 --> 00:13:47,600
been able to see

356
00:13:53,829 --> 00:13:51,839
cold

357
00:13:56,230 --> 00:13:53,839
relatively distant giants like jupiter

358
00:13:57,509 --> 00:13:56,240
and saturn seem to be relatively rare

359
00:13:58,550 --> 00:13:57,519
there are the eccentric giants but

360
00:14:00,389 --> 00:13:58,560
they're quite different because they

361
00:14:01,350 --> 00:14:00,399
loop in close to their stars and become

362
00:14:03,670 --> 00:14:01,360
warm

363
00:14:06,230 --> 00:14:03,680
jupiter and saturn stay out

364
00:14:08,710 --> 00:14:06,240
beyond where water can survive

365
00:14:10,150 --> 00:14:08,720
and that as far as we can tell so far is

366
00:14:12,069 --> 00:14:10,160
rare but that's just at the limit of our

367
00:14:20,470 --> 00:14:12,079
knowledge now we're just being beginning

368
00:14:25,350 --> 00:14:23,430
another interesting difference between

369
00:14:27,430 --> 00:14:25,360
our solar system and

370
00:14:31,110 --> 00:14:27,440
these other new ones

371
00:14:33,189 --> 00:14:31,120
is that we have nothing in size

372
00:14:35,350 --> 00:14:33,199
between the earth

373
00:14:38,550 --> 00:14:35,360
and uranus and neptune which are about

374
00:14:39,829 --> 00:14:38,560
four times the earth's diameter

375
00:14:41,990 --> 00:14:39,839
they're very different in composition

376
00:14:42,870 --> 00:14:42,000
the earth is of course mostly rock and

377
00:14:45,030 --> 00:14:42,880
metal

378
00:14:47,030 --> 00:14:45,040
uranus and neptune have a core inside of

379
00:14:49,189 --> 00:14:47,040
rock and metal and then

380
00:14:53,189 --> 00:14:49,199
ice as well and then some gas some

381
00:14:56,230 --> 00:14:53,199
hydrogen and helium on the outside

382
00:14:57,750 --> 00:14:56,240
but when we look at the population of

383
00:14:59,670 --> 00:14:57,760
planets

384
00:15:02,870 --> 00:14:59,680
around the other stars we see something

385
00:15:05,030 --> 00:15:02,880
quite different so here this is a a bar

386
00:15:06,470 --> 00:15:05,040
chart so the average number of planets

387
00:15:08,870 --> 00:15:06,480
per star

388
00:15:12,629 --> 00:15:08,880
versus the radius of the planet so for

389
00:15:15,189 --> 00:15:12,639
example about 10 percent of these stars

390
00:15:20,550 --> 00:15:15,199
have planets between the earth's radius

391
00:15:25,269 --> 00:15:21,990
but then the interesting thing is that

392
00:15:27,829 --> 00:15:25,279
another 10 percent have have planets

393
00:15:29,189 --> 00:15:27,839
with radii between 1.4 and 2 times

394
00:15:30,310 --> 00:15:29,199
earth's radius and then yet another

395
00:15:31,110 --> 00:15:30,320
percent

396
00:15:33,189 --> 00:15:31,120
have

397
00:15:35,030 --> 00:15:33,199
planets in this next range up and it's

398
00:15:37,430 --> 00:15:35,040
only when we get up to here about four

399
00:15:39,030 --> 00:15:37,440
that our solar system has another one so

400
00:15:40,710 --> 00:15:39,040
the interesting thing is that we have a

401
00:15:42,389 --> 00:15:40,720
couple of planets here a couple of

402
00:15:44,870 --> 00:15:42,399
planets here and nothing in between and

403
00:15:46,629 --> 00:15:44,880
yet these are the most common among the

404
00:15:48,069 --> 00:15:46,639
ones we've been able to find around

405
00:15:50,150 --> 00:15:48,079
other stars

406
00:15:52,550 --> 00:15:50,160
so that's a mystery why why are we

407
00:15:54,230 --> 00:15:52,560
different again

408
00:15:56,470 --> 00:15:54,240
another thing that we can see here is

409
00:15:58,790 --> 00:15:56,480
that when we get down to so jupiter is

410
00:16:00,550 --> 00:15:58,800
about 11 times

411
00:16:02,629 --> 00:16:00,560
uh the earth's radius and saturn is

412
00:16:04,629 --> 00:16:02,639
about nine so they both fall in this

413
00:16:06,069 --> 00:16:04,639
bump here so you can see there's a steep

414
00:16:07,509 --> 00:16:06,079
fall off here and then a less steep

415
00:16:09,269 --> 00:16:07,519
falloff and

416
00:16:10,949 --> 00:16:09,279
there's this little bump here

417
00:16:13,189 --> 00:16:10,959
maybe that's telling us something about

418
00:16:15,670 --> 00:16:13,199
how these planets form maybe it's a bit

419
00:16:17,189 --> 00:16:15,680
more difficult as you grow as you try to

420
00:16:19,110 --> 00:16:17,199
form bigger and bigger planets either

421
00:16:21,110 --> 00:16:19,120
it's more difficult to form them or once

422
00:16:22,629 --> 00:16:21,120
they're formed they quickly grow until

423
00:16:24,550 --> 00:16:22,639
they come up to this size and then they

424
00:16:31,030 --> 00:16:24,560
stick there there's something special

425
00:16:34,949 --> 00:16:32,949
we have a little bit more information

426
00:16:37,829 --> 00:16:34,959
than just the radius

427
00:16:39,269 --> 00:16:37,839
for at least some of these new planets

428
00:16:40,949 --> 00:16:39,279
so we for some of them we can also

429
00:16:42,710 --> 00:16:40,959
measure the mass if we can see the

430
00:16:44,870 --> 00:16:42,720
radial velocity if we can see how the

431
00:16:47,110 --> 00:16:44,880
planet uh is driving its star then that

432
00:16:48,710 --> 00:16:47,120
tells us the mass in addition to seeing

433
00:16:51,590 --> 00:16:48,720
the size from how much of the star's

434
00:16:53,350 --> 00:16:51,600
light it blocks and if we put those two

435
00:16:54,870 --> 00:16:53,360
pieces of information together we can

436
00:16:57,110 --> 00:16:54,880
get the density

437
00:16:59,829 --> 00:16:57,120
so here the planet radius is plotted in

438
00:17:01,590 --> 00:16:59,839
earth radia radii the planet mass in

439
00:17:04,309 --> 00:17:01,600
earth masses so the earth is right here

440
00:17:05,029 --> 00:17:04,319
at one and one and venus is just below

441
00:17:09,350 --> 00:17:05,039
it

442
00:17:12,230 --> 00:17:09,360
our solar system is uranus up at the top

443
00:17:13,590 --> 00:17:12,240
right there about four earth radii and

444
00:17:15,189 --> 00:17:13,600
about 14

445
00:17:17,510 --> 00:17:15,199
earth masses

446
00:17:18,549 --> 00:17:17,520
and you can see that there is a lot in

447
00:17:21,029 --> 00:17:18,559
between

448
00:17:23,350 --> 00:17:21,039
um in this region that is completely

449
00:17:24,949 --> 00:17:23,360
unpopulated in our solar system

450
00:17:26,949 --> 00:17:24,959
so each of these colored points is one

451
00:17:28,710 --> 00:17:26,959
of the newly discovered planets we're a

452
00:17:31,430 --> 00:17:28,720
little bit uncertain on their masses and

453
00:17:33,830 --> 00:17:31,440
a bit less uncertain on their radii

454
00:17:35,110 --> 00:17:33,840
shown by the bars there

455
00:17:36,950 --> 00:17:35,120
and then

456
00:17:38,630 --> 00:17:36,960
when you put together a mass

457
00:17:41,029 --> 00:17:38,640
a mass and a radius then you get a

458
00:17:43,750 --> 00:17:41,039
density the interesting thing is that in

459
00:17:45,830 --> 00:17:43,760
the top left corner here these planets

460
00:17:47,990 --> 00:17:45,840
have densities less than one gram per

461
00:17:49,669 --> 00:17:48,000
cubic centimeter less than water

462
00:17:52,150 --> 00:17:49,679
so if they were small enough they would

463
00:17:53,430 --> 00:17:52,160
float in a bathtub

464
00:17:55,190 --> 00:17:53,440
and that means that they have to be

465
00:17:57,750 --> 00:17:55,200
mostly gas in order to get the density

466
00:17:58,789 --> 00:17:57,760
that low if you made them out of

467
00:18:00,950 --> 00:17:58,799
out of

468
00:18:03,190 --> 00:18:00,960
earth rocks then they would have then

469
00:18:05,430 --> 00:18:03,200
their mass would increase in this way

470
00:18:07,350 --> 00:18:05,440
with radius if you made if you added

471
00:18:09,270 --> 00:18:07,360
some water it was half rock and half

472
00:18:11,830 --> 00:18:09,280
water it would follow this curve if it

473
00:18:13,510 --> 00:18:11,840
was all water it would be on this curve

474
00:18:15,110 --> 00:18:13,520
and many of these planets are up above

475
00:18:17,270 --> 00:18:15,120
even all water so that means they have

476
00:18:19,430 --> 00:18:17,280
to have some hydrogen and helium mixed

477
00:18:21,430 --> 00:18:19,440
in shown by the the dotted curves there

478
00:18:23,830 --> 00:18:21,440
how much of the hydrogen helium

479
00:18:24,950 --> 00:18:23,840
you need to mix in

480
00:18:26,390 --> 00:18:24,960
so

481
00:18:29,590 --> 00:18:26,400
um

482
00:18:32,390 --> 00:18:29,600
not only do we have planets in this

483
00:18:35,510 --> 00:18:32,400
region in between uh the earth and

484
00:18:37,669 --> 00:18:35,520
uranus and neptune in size but also

485
00:18:40,470 --> 00:18:37,679
they're quite different in composition

486
00:18:43,029 --> 00:18:40,480
they they're fluffy in a way that even

487
00:18:45,430 --> 00:18:43,039
uranus and neptune are not

488
00:18:47,590 --> 00:18:45,440
so there again there are strange beasts

489
00:18:50,150 --> 00:18:47,600
unfamiliar beasts

490
00:18:52,070 --> 00:18:50,160
i didn't mention yet the colours of the

491
00:18:55,350 --> 00:18:52,080
points show how much light they receive

492
00:18:57,110 --> 00:18:55,360
from their star so this is the the flux

493
00:18:59,110 --> 00:18:57,120
in units of the flux that the earth

494
00:19:01,270 --> 00:18:59,120
receives from the sun you can see that

495
00:19:03,110 --> 00:19:01,280
many of the colors are yellow or red

496
00:19:05,510 --> 00:19:03,120
indicating that they receive a hundred a

497
00:19:07,830 --> 00:19:05,520
thousand or even ten thousand times

498
00:19:09,430 --> 00:19:07,840
as much light from their stars because

499
00:19:11,750 --> 00:19:09,440
remember these are close

500
00:19:12,789 --> 00:19:11,760
because we can most easily see the ones

501
00:19:14,950 --> 00:19:12,799
that are

502
00:19:22,230 --> 00:19:14,960
on orbits less than 100 days quite close

503
00:19:28,070 --> 00:19:25,350
but in another way many of these extra

504
00:19:30,390 --> 00:19:28,080
solar planets are quite like the solar

505
00:19:33,510 --> 00:19:30,400
system here's a little map of the solar

506
00:19:35,590 --> 00:19:33,520
system as seen from the side

507
00:19:37,029 --> 00:19:35,600
uh so the sun is here and the planets

508
00:19:39,430 --> 00:19:37,039
are lined up

509
00:19:40,470 --> 00:19:39,440
uh with the the planes of their orbits

510
00:19:42,870 --> 00:19:40,480
shown by

511
00:19:45,590 --> 00:19:42,880
uh the the lines here and the one that

512
00:19:47,029 --> 00:19:45,600
tilts the most out of the plane of of

513
00:19:48,789 --> 00:19:47,039
all of the rest is mercury and it's

514
00:19:50,630 --> 00:19:48,799
about six degrees

515
00:19:52,310 --> 00:19:50,640
and the others are uh are all less than

516
00:19:54,549 --> 00:19:52,320
that so the numbers are listed down here

517
00:19:57,110 --> 00:19:54,559
many of them are less than one degree

518
00:19:59,270 --> 00:19:57,120
the earth is only 1.6

519
00:20:01,909 --> 00:19:59,280
so they're basically all lying in one

520
00:20:04,710 --> 00:20:01,919
plane and that's consistent at any rate

521
00:20:06,470 --> 00:20:04,720
with them all having formed together

522
00:20:08,710 --> 00:20:06,480
out of the same material

523
00:20:10,710 --> 00:20:08,720
so they they all share

524
00:20:12,549 --> 00:20:10,720
not quite share in orbit but they have

525
00:20:13,830 --> 00:20:12,559
orbits of different sizes in the same

526
00:20:16,070 --> 00:20:13,840
plane

527
00:20:18,310 --> 00:20:16,080
and we know that many of the uh the

528
00:20:20,070 --> 00:20:18,320
planets around other stars the systems

529
00:20:22,710 --> 00:20:20,080
that have multiple planets must be like

530
00:20:24,470 --> 00:20:22,720
that too because we see them go fro in

531
00:20:26,470 --> 00:20:24,480
front of the face of their star one by

532
00:20:28,149 --> 00:20:26,480
one one after the other and so that

533
00:20:29,510 --> 00:20:28,159
means again they have to lie very close

534
00:20:31,510 --> 00:20:29,520
to the same plane otherwise they would

535
00:20:34,310 --> 00:20:31,520
pass above the star or below it and we

536
00:20:36,149 --> 00:20:34,320
would not see those transits

537
00:20:37,909 --> 00:20:36,159
so in this way

538
00:20:39,830 --> 00:20:37,919
the the other planets

539
00:20:41,270 --> 00:20:39,840
are similar to ours and perhaps that's

540
00:20:46,230 --> 00:20:41,280
saying that in some respects the way

541
00:20:50,230 --> 00:20:48,390
but some of the hot jupiters break this

542
00:20:52,310 --> 00:20:50,240
rule

543
00:20:55,110 --> 00:20:52,320
uh this is one that was found with the

544
00:20:57,029 --> 00:20:55,120
ground-based telescope so a wide-angle

545
00:20:58,149 --> 00:20:57,039
search for planets i think is is its

546
00:20:59,029 --> 00:20:58,159
moniker

547
00:21:03,190 --> 00:20:59,039
and

548
00:21:05,669 --> 00:21:03,200
here are showing the star is rotating

549
00:21:08,870 --> 00:21:05,679
like this around a vertical axis

550
00:21:10,870 --> 00:21:08,880
and yet the planet is uh plunging along

551
00:21:13,430 --> 00:21:10,880
this line here

552
00:21:15,110 --> 00:21:13,440
up and down around so it's almost the

553
00:21:18,390 --> 00:21:15,120
plane of its orbit is almost

554
00:21:20,310 --> 00:21:18,400
perpendicular to the equator of its star

555
00:21:22,390 --> 00:21:20,320
and this suggests that something violent

556
00:21:32,310 --> 00:21:22,400
has happened to uh to push it away from

557
00:21:36,710 --> 00:21:34,630
so finally i'd like to get on to the

558
00:21:39,190 --> 00:21:36,720
part that's speculation and this is what

559
00:21:42,310 --> 00:21:39,200
i do for my day job so i'm very happy to

560
00:21:44,870 --> 00:21:43,190
so

561
00:21:46,870 --> 00:21:44,880
we don't know the whole whole story of

562
00:21:48,390 --> 00:21:46,880
how they're born we're still trying to

563
00:21:50,789 --> 00:21:48,400
piece it together

564
00:21:52,630 --> 00:21:50,799
i'll try to try to outline a few of the

565
00:21:54,070 --> 00:21:52,640
chapters a few of the things that we

566
00:22:00,710 --> 00:21:54,080
think may have happened even if we don't

567
00:22:05,990 --> 00:22:03,590
so first around many young stars we see

568
00:22:07,350 --> 00:22:06,000
orbiting clouds of dust and gas like

569
00:22:10,230 --> 00:22:07,360
this one

570
00:22:14,310 --> 00:22:10,240
so the star here is hidden so

571
00:22:16,149 --> 00:22:14,320
there's a disk of of uh opaque material

572
00:22:18,630 --> 00:22:16,159
around the star and it happens in this

573
00:22:20,390 --> 00:22:18,640
case to be seen edge on so we can't see

574
00:22:21,830 --> 00:22:20,400
the star directly

575
00:22:23,590 --> 00:22:21,840
instead

576
00:22:26,549 --> 00:22:23,600
what happens is that some of the dust

577
00:22:29,029 --> 00:22:26,559
and gas lies above and below the disc

578
00:22:30,630 --> 00:22:29,039
and that especially the dust there

579
00:22:33,270 --> 00:22:30,640
reflects the starlight scatters the

580
00:22:35,990 --> 00:22:33,280
starlight towards us so this light above

581
00:22:38,789 --> 00:22:36,000
and below the disc is the uh

582
00:22:40,870 --> 00:22:38,799
is the material the low density material

583
00:22:42,789 --> 00:22:40,880
in the outskirts of this cloud

584
00:22:44,549 --> 00:22:42,799
bouncing the starlight so that we can

585
00:22:46,630 --> 00:22:44,559
see it

586
00:22:49,990 --> 00:22:46,640
you can see the the line is a little bit

587
00:22:51,830 --> 00:22:50,000
red here because some some of the dust

588
00:22:55,669 --> 00:22:51,840
the denser dust is absorbing some of the

589
00:22:59,590 --> 00:22:57,750
so the typical size for this cloud is

590
00:23:02,070 --> 00:22:59,600
about the size of the solar system or a

591
00:23:05,669 --> 00:23:02,080
little bit bigger so that's good because

592
00:23:08,549 --> 00:23:05,679
we need to form a planetary system

593
00:23:10,310 --> 00:23:08,559
the mass in it is about enough to form

594
00:23:12,789 --> 00:23:10,320
the planets

595
00:23:14,070 --> 00:23:12,799
plus some extra hydrogen and helium so

596
00:23:15,350 --> 00:23:14,080
that's one of the problems that we have

597
00:23:19,350 --> 00:23:15,360
to solve we have to get rid of that

598
00:23:20,230 --> 00:23:19,360
extra gas to leave the planets behind

599
00:23:22,870 --> 00:23:20,240
and

600
00:23:25,029 --> 00:23:22,880
we don't we can't uh watch one of these

601
00:23:26,870 --> 00:23:25,039
and see how long it lives

602
00:23:28,549 --> 00:23:26,880
because it lives for a few million years

603
00:23:30,710 --> 00:23:28,559
but we can look at

604
00:23:33,110 --> 00:23:30,720
star clusters of different ages we can

605
00:23:35,029 --> 00:23:33,120
work out the ages by studying the stars

606
00:23:37,350 --> 00:23:35,039
and we can see that around clusters that

607
00:23:39,190 --> 00:23:37,360
are more than a few million years old

608
00:23:40,710 --> 00:23:39,200
almost none of the stars still have

609
00:23:42,149 --> 00:23:40,720
these clouds

610
00:23:43,669 --> 00:23:42,159
so from that

611
00:23:46,070 --> 00:23:43,679
we guess

612
00:23:47,830 --> 00:23:46,080
it's an educated guest that

613
00:23:48,950 --> 00:23:47,840
they live for a few million years that's

614
00:23:51,750 --> 00:23:48,960
the amount of time that we have

615
00:23:52,950 --> 00:23:51,760
available to collect together these

616
00:23:56,549 --> 00:23:52,960
interstellar

617
00:23:58,070 --> 00:23:56,559
tiny submicron sized grains of dust

618
00:24:02,230 --> 00:23:58,080
collect them together in their trillions

619
00:24:07,350 --> 00:24:04,710
another thing is that um

620
00:24:09,510 --> 00:24:07,360
if we if we work out how long it would

621
00:24:11,909 --> 00:24:09,520
take for this dust to settle down for

622
00:24:13,909 --> 00:24:11,919
all of this extra dust out here to

623
00:24:15,269 --> 00:24:13,919
collapse down and form a thin line in

624
00:24:16,070 --> 00:24:15,279
the middle

625
00:24:18,149 --> 00:24:16,080
it's

626
00:24:20,870 --> 00:24:18,159
maybe a few thousand years something in

627
00:24:24,149 --> 00:24:20,880
that ballpark so it's much less than the

628
00:24:25,750 --> 00:24:24,159
lifetimes of these clouds so that means

629
00:24:27,909 --> 00:24:25,760
that something has to be keeping the

630
00:24:29,029 --> 00:24:27,919
dust stirred up and preventing it from

631
00:24:30,830 --> 00:24:29,039
settling

632
00:24:33,350 --> 00:24:30,840
and that something is probably

633
00:24:35,110 --> 00:24:33,360
turbulence and that turbulence

634
00:24:40,870 --> 00:24:35,120
has a role to play in forming the

635
00:24:46,549 --> 00:24:43,510
from modeling in the computer we know

636
00:24:49,029 --> 00:24:46,559
that if you have a magnetic field

637
00:24:51,430 --> 00:24:49,039
and if the gas is ionized enough so that

638
00:24:55,590 --> 00:24:51,440
it can feel the magnetic forces

639
00:24:57,430 --> 00:24:55,600
then the forces drive turbulence

640
00:24:58,870 --> 00:24:57,440
a magnetic field connects material close

641
00:25:01,190 --> 00:24:58,880
to the star with material a little bit

642
00:25:02,870 --> 00:25:01,200
further away and pushes the further away

643
00:25:04,630 --> 00:25:02,880
stuff onto a higher orbit while letting

644
00:25:05,830 --> 00:25:04,640
the closer stuff spiral into a lower

645
00:25:07,510 --> 00:25:05,840
orbit

646
00:25:09,590 --> 00:25:07,520
some of it eventually will spiral right

647
00:25:11,190 --> 00:25:09,600
in and and um

648
00:25:13,430 --> 00:25:11,200
collapse down onto the surface of the

649
00:25:15,190 --> 00:25:13,440
star so the star will grow a bit on the

650
00:25:17,350 --> 00:25:15,200
other hand the outer reaches of it are

651
00:25:19,830 --> 00:25:17,360
going to spread and the disc will get

652
00:25:21,830 --> 00:25:19,840
get bigger over time

653
00:25:24,230 --> 00:25:21,840
but all of that relies on

654
00:25:26,070 --> 00:25:24,240
on having enough ionization

655
00:25:27,190 --> 00:25:26,080
so it can couple to magnetic fields and

656
00:25:33,350 --> 00:25:27,200
we don't know

657
00:25:37,350 --> 00:25:35,590
we can even see planet formation

658
00:25:40,070 --> 00:25:37,360
beginning

659
00:25:41,909 --> 00:25:40,080
here is an image from a giant new radio

660
00:25:46,230 --> 00:25:41,919
telescope that's still being assembled

661
00:25:48,230 --> 00:25:46,240
in the atacama desert in south america

662
00:25:50,549 --> 00:25:48,240
it shows the disc around a young star

663
00:25:53,190 --> 00:25:50,559
which is at the center here

664
00:25:55,350 --> 00:25:53,200
and at radio wavelengths the telescope

665
00:25:57,750 --> 00:25:55,360
is sensitive to

666
00:25:58,950 --> 00:25:57,760
pebble sized or sand grain sized

667
00:26:00,149 --> 00:25:58,960
particles

668
00:26:01,510 --> 00:26:00,159
which means they're far bigger than

669
00:26:02,630 --> 00:26:01,520
anything in the interstellar medium so

670
00:26:04,710 --> 00:26:02,640
that means at least the very early

671
00:26:06,870 --> 00:26:04,720
stages of planet formation

672
00:26:12,070 --> 00:26:06,880
have begun

673
00:26:16,070 --> 00:26:13,669
there are rings you can see that the

674
00:26:18,470 --> 00:26:16,080
dust seems to be gathered together so

675
00:26:19,750 --> 00:26:18,480
there are rings and gaps and more rings

676
00:26:21,430 --> 00:26:19,760
and more gaps

677
00:26:24,710 --> 00:26:21,440
and astronomers are still debating this

678
00:26:27,269 --> 00:26:24,720
is a new result in the last year

679
00:26:30,230 --> 00:26:27,279
maybe it's planets maybe it's the uh the

680
00:26:31,990 --> 00:26:30,240
tides of planets orbiting within it that

681
00:26:33,590 --> 00:26:32,000
uh so perhaps a planet has cleared this

682
00:26:34,789 --> 00:26:33,600
gap and another one has cleared this gap

683
00:26:37,269 --> 00:26:34,799
and so on

684
00:26:39,190 --> 00:26:37,279
but another possibility is that perhaps

685
00:26:40,630 --> 00:26:39,200
what's happening instead is that the

686
00:26:41,590 --> 00:26:40,640
dust particles are starting to stick

687
00:26:45,269 --> 00:26:41,600
together

688
00:26:47,750 --> 00:26:45,279
in regions where you're near the

689
00:26:50,310 --> 00:26:47,760
threshold for uh for vaporizing one of

690
00:26:52,789 --> 00:26:50,320
the materials that makes up the ices

691
00:26:55,510 --> 00:26:52,799
some of these these gaps seem to seem to

692
00:26:57,909 --> 00:26:55,520
correspond to those locations for uh for

693
00:27:00,470 --> 00:26:57,919
evaporating different ices

694
00:27:02,230 --> 00:27:00,480
and yet another possibility is that this

695
00:27:04,310 --> 00:27:02,240
material is dense enough to begin under

696
00:27:06,870 --> 00:27:04,320
its own gravity begin to accumulate

697
00:27:08,710 --> 00:27:06,880
together to build up these rings so you

698
00:27:10,789 --> 00:27:08,720
can see there are lots of possibilities

699
00:27:17,990 --> 00:27:10,799
and we have a lot of work to do to sort

700
00:27:23,110 --> 00:27:21,430
once we get beyond that pebble size we

701
00:27:25,190 --> 00:27:23,120
can't see what happens

702
00:27:26,710 --> 00:27:25,200
if you have a trillion dust grains

703
00:27:28,789 --> 00:27:26,720
floating around they have a lot of

704
00:27:31,750 --> 00:27:28,799
surface area but if you collect them

705
00:27:34,549 --> 00:27:31,760
together into a compact ball they have

706
00:27:35,990 --> 00:27:34,559
much less area and so they don't emit

707
00:27:37,909 --> 00:27:36,000
at all basically they have their

708
00:27:40,549 --> 00:27:37,919
emission is far too feeble

709
00:27:42,950 --> 00:27:40,559
for even the best of our telescopes to

710
00:27:46,070 --> 00:27:42,960
uh to see them

711
00:27:47,990 --> 00:27:46,080
but it seems likely that planets form

712
00:27:49,029 --> 00:27:48,000
easiest a little bit further out than

713
00:27:53,510 --> 00:27:49,039
the earth

714
00:27:55,590 --> 00:27:53,520
hot for water ice to survive

715
00:27:57,350 --> 00:27:55,600
as you can tell from seeing that comets

716
00:27:58,549 --> 00:27:57,360
when they pass the earth orbit begin to

717
00:28:00,549 --> 00:27:58,559
evaporate

718
00:28:02,549 --> 00:28:00,559
but if you go a bit further out you

719
00:28:03,669 --> 00:28:02,559
still have quite a lot of material

720
00:28:05,909 --> 00:28:03,679
and yet

721
00:28:07,990 --> 00:28:05,919
the water can survive

722
00:28:09,350 --> 00:28:08,000
this picture is taking it to the extreme

723
00:28:12,149 --> 00:28:09,360
this is an artist's impression of the

724
00:28:13,830 --> 00:28:12,159
surface of pluto and the sun is so far

725
00:28:16,389 --> 00:28:13,840
away that it's just a bright star and

726
00:28:18,470 --> 00:28:16,399
that's why pluto is so cold

727
00:28:20,230 --> 00:28:18,480
and for the same reason the

728
00:28:22,310 --> 00:28:20,240
outer reaches of the early solar system

729
00:28:24,389 --> 00:28:22,320
are a good place to build planets

730
00:28:26,870 --> 00:28:24,399
because you have a lot of ices and if

731
00:28:28,630 --> 00:28:26,880
you take the ice and add it to the rock

732
00:28:29,909 --> 00:28:28,640
then you triple or quadruple the amount

733
00:28:31,190 --> 00:28:29,919
of solid material that you have

734
00:28:32,149 --> 00:28:31,200
available

735
00:28:34,310 --> 00:28:32,159
so

736
00:28:39,029 --> 00:28:34,320
that's a good that helps in many ways to

737
00:28:43,350 --> 00:28:41,110
but if we form the planets in the outer

738
00:28:46,070 --> 00:28:43,360
solar system why are there so many of

739
00:28:47,029 --> 00:28:46,080
these planets around other stars close

740
00:28:51,990 --> 00:28:47,039
in

741
00:28:54,630 --> 00:28:52,000
the planet the young planet has to up

742
00:29:01,029 --> 00:28:54,640
and pack its bags and somehow

743
00:29:06,310 --> 00:29:03,990
one possibility is that they migrate

744
00:29:08,710 --> 00:29:06,320
inwards by interacting with the gas

745
00:29:10,950 --> 00:29:08,720
around them so here's a movie from

746
00:29:11,750 --> 00:29:10,960
another computer simulation

747
00:29:14,389 --> 00:29:11,760
and

748
00:29:16,230 --> 00:29:14,399
to look at things in detail uh even on

749
00:29:18,149 --> 00:29:16,240
the big computers that we have today we

750
00:29:21,190 --> 00:29:18,159
have to look at a small patch

751
00:29:24,149 --> 00:29:21,200
so our camera here is staying fixed on

752
00:29:25,830 --> 00:29:24,159
the planet as it orbits around the star

753
00:29:27,510 --> 00:29:25,840
you can see that material on the left

754
00:29:29,750 --> 00:29:27,520
side of the screen here is orbiting

755
00:29:31,669 --> 00:29:29,760
faster so it moves up relative to the

756
00:29:32,950 --> 00:29:31,679
planet material on the right side of the

757
00:29:34,470 --> 00:29:32,960
screen is orbiting slower because it's

758
00:29:37,590 --> 00:29:34,480
further from the star so it appears to

759
00:29:39,269 --> 00:29:37,600
move down relative to the planet

760
00:29:41,350 --> 00:29:39,279
and you can see that despite the

761
00:29:43,190 --> 00:29:41,360
turbulence that makes this calculation

762
00:29:45,350 --> 00:29:43,200
messy there's overall there's a spiral

763
00:29:48,470 --> 00:29:45,360
arm pattern here so material that

764
00:29:51,029 --> 00:29:48,480
approaches the planet from below

765
00:29:52,789 --> 00:29:51,039
going faster it gets pulled a little bit

766
00:29:54,310 --> 00:29:52,799
towards the planet

767
00:29:57,510 --> 00:29:54,320
and that deflection means that there's

768
00:29:58,870 --> 00:29:57,520
extra material in this spiral arm

769
00:30:00,389 --> 00:29:58,880
downstream

770
00:30:01,750 --> 00:30:00,399
same thing happens on the other side for

771
00:30:03,830 --> 00:30:01,760
material that's lagging behind the

772
00:30:06,310 --> 00:30:03,840
planet once it's attracted to the planet

773
00:30:09,430 --> 00:30:06,320
it then collects into this spiral arm on

774
00:30:11,510 --> 00:30:09,440
the other side and each spiral arm

775
00:30:13,990 --> 00:30:11,520
exerts a force on the planet through its

776
00:30:16,710 --> 00:30:14,000
gravity but the forces aren't quite the

777
00:30:18,950 --> 00:30:16,720
same the typically

778
00:30:20,630 --> 00:30:18,960
the arm on the outside exerts a slightly

779
00:30:22,149 --> 00:30:20,640
bigger force

780
00:30:24,389 --> 00:30:22,159
and that means that the planet is

781
00:30:25,990 --> 00:30:24,399
gradually going to drift in

782
00:30:28,070 --> 00:30:26,000
towards the star

783
00:30:29,430 --> 00:30:28,080
over time it could approach the star

784
00:30:32,149 --> 00:30:29,440
very closely

785
00:30:36,630 --> 00:30:32,159
so this may be a good way to make those

786
00:30:38,950 --> 00:30:36,640
tightly packed systems of planets

787
00:30:40,549 --> 00:30:38,960
there is another way to get the planets

788
00:30:42,789 --> 00:30:40,559
in close which works at least for the

789
00:30:45,750 --> 00:30:42,799
hot jupiters

790
00:30:47,590 --> 00:30:45,760
and it involves tides just like the

791
00:30:49,669 --> 00:30:47,600
tides on the earth

792
00:30:51,669 --> 00:30:49,679
so if we have

793
00:30:54,549 --> 00:30:51,679
a distant jupiter

794
00:30:56,149 --> 00:30:54,559
it encounters another of its kind

795
00:30:57,909 --> 00:30:56,159
so it's scattered onto an eccentric

796
00:31:00,230 --> 00:30:57,919
orbit so it's looping in close to the

797
00:31:02,549 --> 00:31:00,240
sun and out again back to near where it

798
00:31:05,909 --> 00:31:02,559
started but when it's in close its

799
00:31:08,230 --> 00:31:05,919
gravity raises tides on its star

800
00:31:10,870 --> 00:31:08,240
and just as tides on the earth get

801
00:31:13,190 --> 00:31:10,880
dissipated by moving around the land

802
00:31:14,710 --> 00:31:13,200
masses tides in the star also get

803
00:31:16,310 --> 00:31:14,720
dissipated the star gets a little bit of

804
00:31:18,470 --> 00:31:16,320
extra heat from that

805
00:31:20,710 --> 00:31:18,480
and the planets orbit the outer end of

806
00:31:21,830 --> 00:31:20,720
its orbit grows shorter and shorter and

807
00:31:24,549 --> 00:31:21,840
it can

808
00:31:28,549 --> 00:31:24,559
eventually end up um

809
00:31:30,630 --> 00:31:28,559
in a a close orbit uh in tide around its

810
00:31:32,789 --> 00:31:30,640
star so here's what the tides do on

811
00:31:34,549 --> 00:31:32,799
earth

812
00:31:36,310 --> 00:31:34,559
you can see it's easy to get out to the

813
00:31:37,590 --> 00:31:36,320
lighthouse at low tide and not at high

814
00:31:40,789 --> 00:31:37,600
tide

815
00:31:42,470 --> 00:31:40,799
so twice per rotation of the earth the

816
00:31:44,549 --> 00:31:42,480
gravity of the moon is pulling the ocean

817
00:31:46,389 --> 00:31:44,559
up and the same thing happens on the

818
00:31:50,950 --> 00:31:46,399
star

819
00:31:53,029 --> 00:31:50,960
gravity of its planet

820
00:31:55,269 --> 00:31:53,039
will uh pull the tides up and then the

821
00:31:56,789 --> 00:31:55,279
tides will dissipate into heat that

822
00:31:58,710 --> 00:31:56,799
removes energy

823
00:32:00,950 --> 00:31:58,720
from the orbit so this is a second way

824
00:32:02,710 --> 00:32:00,960
that we could make

825
00:32:06,950 --> 00:32:02,720
at least the hot jupiters be close to

826
00:32:09,669 --> 00:32:07,830
so i

827
00:32:11,590 --> 00:32:09,679
i see that i've come

828
00:32:14,230 --> 00:32:11,600
almost to the end already so i have

829
00:32:16,149 --> 00:32:14,240
plenty of time for questions

830
00:32:18,470 --> 00:32:16,159
these are the

831
00:32:21,190 --> 00:32:18,480
questions that we haven't answered but

832
00:32:26,070 --> 00:32:21,200
would like to these are the things that

833
00:32:30,950 --> 00:32:27,909
first how did the planetary systems come

834
00:32:33,029 --> 00:32:30,960
to be so different from one another

835
00:32:35,350 --> 00:32:33,039
um

836
00:32:37,430 --> 00:32:35,360
uh we've seen that some systems have hot

837
00:32:38,950 --> 00:32:37,440
jupiters and relatively few other

838
00:32:42,149 --> 00:32:38,960
planets the hot jupiters seem to be

839
00:32:43,830 --> 00:32:42,159
accompanied by uh fewer companions than

840
00:32:49,110 --> 00:32:43,840
other systems

841
00:32:49,990 --> 00:32:49,120
have the eccentric giants

842
00:32:52,470 --> 00:32:50,000
where

843
00:32:54,710 --> 00:32:52,480
there's a big body that plunges through

844
00:32:56,710 --> 00:32:54,720
the inner parts of the planetary system

845
00:32:59,430 --> 00:32:56,720
and out again so they must have had some

846
00:33:01,990 --> 00:32:59,440
kind of violent event in their past

847
00:33:04,710 --> 00:33:02,000
why do some systems have those those

848
00:33:07,750 --> 00:33:04,720
violent happenings and others do not

849
00:33:09,669 --> 00:33:07,760
and we've seen that yet other systems uh

850
00:33:12,389 --> 00:33:09,679
have several planets packed in close

851
00:33:13,190 --> 00:33:12,399
around their star where our solar system

852
00:33:14,789 --> 00:33:13,200
has

853
00:33:16,950 --> 00:33:14,799
basically nothing

854
00:33:18,230 --> 00:33:16,960
and so what's different about about the

855
00:33:21,909 --> 00:33:18,240
history

856
00:33:24,549 --> 00:33:21,919
of our solar system

857
00:33:26,710 --> 00:33:24,559
we have four coal giants also on orbits

858
00:33:29,269 --> 00:33:26,720
that are nearly circular and that uh

859
00:33:31,430 --> 00:33:29,279
seems to be unusual what's special about

860
00:33:32,470 --> 00:33:31,440
our solar system were we

861
00:33:33,830 --> 00:33:32,480
um

862
00:33:36,070 --> 00:33:33,840
lucky in a way that we didn't have a

863
00:33:37,750 --> 00:33:36,080
violent event in the outer reaches and

864
00:33:40,950 --> 00:33:37,760
yet unlucky in that something special

865
00:33:42,789 --> 00:33:40,960
happened close into the sun

866
00:33:45,990 --> 00:33:42,799
we don't know it's still to be

867
00:33:48,230 --> 00:33:46,000
investigated and finally working towards

868
00:33:50,630 --> 00:33:48,240
uh

869
00:33:52,230 --> 00:33:50,640
finding other earths we'd like to know

870
00:33:53,750 --> 00:33:52,240
what the ones that we can see so far the

871
00:33:56,230 --> 00:33:53,760
ones that are just a little bit bigger

872
00:33:58,789 --> 00:33:56,240
than the earth what they are made of

873
00:34:00,950 --> 00:33:58,799
um and then how were they put together

874
00:34:02,710 --> 00:34:00,960
why do some of them have the that fluffy

875
00:34:05,509 --> 00:34:02,720
composition why they

876
00:34:06,870 --> 00:34:05,519
uh gas to a far bigger extent than the

877
00:34:11,030 --> 00:34:06,880
earth

878
00:34:12,470 --> 00:34:11,040
we find any that are rocky and yet they

879
00:34:15,190 --> 00:34:12,480
do have

880
00:34:19,190 --> 00:34:15,200
an atmosphere that we might recognize

881
00:34:24,790 --> 00:34:23,349
so uh i'll put back up my my starting

882
00:34:28,550 --> 00:34:24,800
slide

883
00:34:34,710 --> 00:34:31,909
and maybe i can say also

884
00:34:37,270 --> 00:34:34,720
i talked about migration for the for the

885
00:34:39,030 --> 00:34:37,280
giant planets but for the small

886
00:34:41,349 --> 00:34:39,040
rocky planets we'd like to know how they

887
00:34:43,270 --> 00:34:41,359
migrate too this artist's impression is

888
00:34:45,349 --> 00:34:43,280
showing uh uh

889
00:34:48,629 --> 00:34:45,359
what happens when you have some uh rocky

890
00:34:51,270 --> 00:34:48,639
material in close to the star

891
00:34:53,349 --> 00:34:51,280
i think the evidence from the fact that

892
00:34:55,669 --> 00:34:53,359
so many of those small planets are

893
00:34:57,670 --> 00:34:55,679
coplanar suggests that they must have

894
00:35:00,069 --> 00:34:57,680
undergone migration too i think that's

895
00:35:02,390 --> 00:35:00,079
probably the common thread because in

896
00:35:03,990 --> 00:35:02,400
our solar system

897
00:35:06,390 --> 00:35:04,000
all the planets share a plane in those

898
00:35:08,310 --> 00:35:06,400
other systems they do too and so it has

899
00:35:09,190 --> 00:35:08,320
to be that

900
00:35:14,790 --> 00:35:09,200
they

901
00:35:16,230 --> 00:35:14,800
so i i've come to the end so i'll be

902
00:35:30,550 --> 00:35:16,240
very grateful to take any of your

903
00:35:35,510 --> 00:35:33,750
i've been told to uh remind you to come

904
00:35:38,790 --> 00:35:35,520
up to the microphone please to ask

905
00:35:50,150 --> 00:35:41,589
that way our viewers online can

906
00:35:55,670 --> 00:35:54,710
my question is regarding the tides

907
00:35:57,829 --> 00:35:55,680
that

908
00:35:59,109 --> 00:35:57,839
between the sun and the planet

909
00:36:02,310 --> 00:35:59,119
that

910
00:36:04,710 --> 00:36:02,320
i believe you mentioned is possibly

911
00:36:06,630 --> 00:36:04,720
responsible for bringing the planets

912
00:36:09,109 --> 00:36:06,640
closer to the sun

913
00:36:10,390 --> 00:36:09,119
and um

914
00:36:12,230 --> 00:36:10,400
i'm wondering

915
00:36:13,670 --> 00:36:12,240
about the difference between that

916
00:36:14,470 --> 00:36:13,680
scenario

917
00:36:18,710 --> 00:36:14,480
and

918
00:36:22,630 --> 00:36:18,720
where um

919
00:36:26,390 --> 00:36:22,640
the earth's rotation has been slowed due

920
00:36:28,310 --> 00:36:26,400
to the top the relationship between

921
00:36:31,190 --> 00:36:28,320
the earth and the moon and the moon

922
00:36:32,790 --> 00:36:31,200
actually is goes further out so i'm

923
00:36:35,270 --> 00:36:32,800
wondering about

924
00:36:37,670 --> 00:36:35,280
if there's a difference or what's going

925
00:36:41,109 --> 00:36:37,680
on there it's it's similar but just a

926
00:36:42,150 --> 00:36:41,119
little bit different so in that case

927
00:36:44,069 --> 00:36:42,160
because

928
00:36:46,870 --> 00:36:44,079
the earth rotates in one day whereas the

929
00:36:48,790 --> 00:36:46,880
moon orbits in 30 days or so

930
00:36:50,550 --> 00:36:48,800
and that means that

931
00:36:51,829 --> 00:36:50,560
the the bulge that the moon raises in

932
00:36:53,510 --> 00:36:51,839
the earth

933
00:36:55,910 --> 00:36:53,520
gets a little bit ahead

934
00:36:57,990 --> 00:36:55,920
of the moon's location in its orbit and

935
00:36:59,750 --> 00:36:58,000
it pulls on the moon and accelerates its

936
00:37:00,630 --> 00:36:59,760
forward and that's why the moon tends to

937
00:37:01,990 --> 00:37:00,640
move

938
00:37:04,950 --> 00:37:02,000
further away

939
00:37:05,990 --> 00:37:04,960
but that's not guaranteed to happen in

940
00:37:07,829 --> 00:37:06,000
in

941
00:37:09,910 --> 00:37:07,839
exoplanet systems so for example you

942
00:37:12,950 --> 00:37:09,920
could have a situation as we actually

943
00:37:15,270 --> 00:37:12,960
have with mars and its two small moons

944
00:37:16,710 --> 00:37:15,280
where they're orbiting inside the point

945
00:37:18,790 --> 00:37:16,720
where they would be

946
00:37:20,230 --> 00:37:18,800
going around once per day

947
00:37:24,150 --> 00:37:20,240
so

948
00:37:25,270 --> 00:37:24,160
they're pulled back by the uh the bulge

949
00:37:27,270 --> 00:37:25,280
on the planet and so they will

950
00:37:31,270 --> 00:37:27,280
eventually crash into the surface i see

951
00:37:38,150 --> 00:37:34,150
i uh yes i was wondering how many uh

952
00:37:41,190 --> 00:37:38,160
main sequence objects you found

953
00:37:43,990 --> 00:37:41,200
in your new study of new planets

954
00:37:46,870 --> 00:37:44,000
and also is it possible

955
00:37:48,829 --> 00:37:46,880
that the stars could migrate through

956
00:37:51,670 --> 00:37:48,839
nuclear

957
00:37:54,310 --> 00:37:51,680
fusion um i guess i'd like to understand

958
00:37:55,910 --> 00:37:54,320
a little bit more about your question so

959
00:37:58,710 --> 00:37:55,920
um

960
00:38:02,870 --> 00:37:58,720
so it is certainly true that as stars

961
00:38:05,349 --> 00:38:02,880
use up the fuel in their insides they do

962
00:38:07,430 --> 00:38:05,359
they tend to expand generally as they

963
00:38:09,270 --> 00:38:07,440
move through their main sequence

964
00:38:10,870 --> 00:38:09,280
life time

965
00:38:12,390 --> 00:38:10,880
and things could get interesting if you

966
00:38:14,950 --> 00:38:12,400
have a hot jupiter

967
00:38:16,790 --> 00:38:14,960
and one of those stars

968
00:38:20,310 --> 00:38:16,800
expands enough so that it approaches the

969
00:38:22,790 --> 00:38:20,320
jupiter's orbit and it could be that the

970
00:38:26,310 --> 00:38:22,800
the planet gets swallowed up

971
00:38:27,750 --> 00:38:26,320
we haven't seen anything like that yet

972
00:38:29,510 --> 00:38:27,760
as far as i know

973
00:38:31,510 --> 00:38:29,520
and that's probably because the

974
00:38:33,510 --> 00:38:31,520
swallowing up happens quickly

975
00:38:35,829 --> 00:38:33,520
once the planet is in the even the low

976
00:38:38,550 --> 00:38:35,839
density upper layers of the star it very

977
00:38:40,150 --> 00:38:38,560
quickly spirals down and is lost

978
00:38:42,150 --> 00:38:40,160
so if we would probably have to look at

979
00:38:43,430 --> 00:38:42,160
a lot of stars until we could get lucky

980
00:38:44,630 --> 00:38:43,440
enough to see

981
00:38:47,230 --> 00:38:44,640
that happen

982
00:38:51,030 --> 00:38:47,240
is it possible though that uh the

983
00:38:54,310 --> 00:38:51,040
geothermal process uh could uh add to

984
00:38:55,109 --> 00:38:54,320
the collapse of the star from the core

985
00:38:58,790 --> 00:38:55,119
well

986
00:38:59,829 --> 00:38:58,800
um even a jupiter has has only about one

987
00:39:02,870 --> 00:38:59,839
one

988
00:39:04,710 --> 00:39:02,880
of the mass of a sun-like star

989
00:39:07,589 --> 00:39:04,720
and so from that point of view it would

990
00:39:09,750 --> 00:39:07,599
only be a small perturbation

991
00:39:11,910 --> 00:39:09,760
it does add a little bit of extra heavy

992
00:39:13,829 --> 00:39:11,920
elements

993
00:39:16,310 --> 00:39:13,839
but they are probably deposited in the

994
00:39:18,310 --> 00:39:16,320
outer layers and so they they would have

995
00:39:21,109 --> 00:39:18,320
only a small effect

996
00:39:22,550 --> 00:39:21,119
on the star's own gravity and probably

997
00:39:24,470 --> 00:39:22,560
little effect on what's happening right

998
00:39:25,510 --> 00:39:24,480
at the core where the nuclear fusion is

999
00:39:27,510 --> 00:39:25,520
ongoing

1000
00:39:29,510 --> 00:39:27,520
but it might be detectable so there are

1001
00:39:33,270 --> 00:39:29,520
some people that

1002
00:39:36,550 --> 00:39:35,190
stars with planets may be a little bit

1003
00:39:38,310 --> 00:39:36,560
enriched in

1004
00:39:40,310 --> 00:39:38,320
heavy elements for example in their

1005
00:39:43,990 --> 00:39:40,320
surface layers

1006
00:39:48,470 --> 00:39:46,710
hi um this is a three-part question

1007
00:39:51,430 --> 00:39:48,480
um i was wondering if you can give us

1008
00:39:54,310 --> 00:39:51,440
examples of the type of violent events

1009
00:39:57,750 --> 00:39:54,320
that would have impacted the planets as

1010
00:40:00,150 --> 00:39:57,760
they formed the second question is um

1011
00:40:02,310 --> 00:40:00,160
would those events occur while the

1012
00:40:03,190 --> 00:40:02,320
planets are forming or after

1013
00:40:05,670 --> 00:40:03,200
and

1014
00:40:08,470 --> 00:40:05,680
have we been able to observe

1015
00:40:10,710 --> 00:40:08,480
any violent events

1016
00:40:11,670 --> 00:40:10,720
with planets that we're looking at now

1017
00:40:13,910 --> 00:40:11,680
um

1018
00:40:15,750 --> 00:40:13,920
yeah that's a third question

1019
00:40:17,510 --> 00:40:15,760
so um

1020
00:40:19,270 --> 00:40:17,520
similar to in the last question so

1021
00:40:20,630 --> 00:40:19,280
because they're violent they tend to be

1022
00:40:22,790 --> 00:40:20,640
over quickly

1023
00:40:24,310 --> 00:40:22,800
and so mostly we see the aftermath we

1024
00:40:27,030 --> 00:40:24,320
see the planets that are on unusual

1025
00:40:33,109 --> 00:40:28,069
so

1026
00:40:36,630 --> 00:40:33,119
years ago

1027
00:40:39,510 --> 00:40:36,640
comet that crashed into jupiter

1028
00:40:41,910 --> 00:40:39,520
and it um that was a violent event it

1029
00:40:43,990 --> 00:40:41,920
happened over just a few years that it

1030
00:40:45,829 --> 00:40:44,000
uh happened to have a close encounter

1031
00:40:47,990 --> 00:40:45,839
and get captured by the planet and then

1032
00:40:50,069 --> 00:40:48,000
it went into jupiter uh crashed into the

1033
00:40:52,470 --> 00:40:50,079
atmosphere fairly quickly

1034
00:40:54,550 --> 00:40:52,480
um and for a similar reason we

1035
00:40:57,589 --> 00:40:54,560
um we would have to get quite lucky to

1036
00:40:58,390 --> 00:40:57,599
see one of these violent events

1037
00:41:00,630 --> 00:40:58,400
um

1038
00:41:02,710 --> 00:41:00,640
the violent events they would probably

1039
00:41:04,950 --> 00:41:02,720
involve a close passage so in the solar

1040
00:41:06,630 --> 00:41:04,960
system um the planets are mutually

1041
00:41:08,470 --> 00:41:06,640
stable they don't interfere with one

1042
00:41:09,430 --> 00:41:08,480
another terribly much

1043
00:41:10,790 --> 00:41:09,440
but

1044
00:41:12,710 --> 00:41:10,800
only just

1045
00:41:15,670 --> 00:41:12,720
so if you were to move jupiter or saturn

1046
00:41:17,589 --> 00:41:15,680
just a little bit towards each other

1047
00:41:19,750 --> 00:41:17,599
then you could

1048
00:41:21,990 --> 00:41:19,760
have them interact enough that they

1049
00:41:23,750 --> 00:41:22,000
would they would uh

1050
00:41:24,950 --> 00:41:23,760
uh get bigger and bigger disturbances

1051
00:41:26,950 --> 00:41:24,960
and eventually have some very close

1052
00:41:28,470 --> 00:41:26,960
passage and then go on to completely new

1053
00:41:31,510 --> 00:41:28,480
orbits

1054
00:41:33,430 --> 00:41:31,520
and um that's the kind of violent event

1055
00:41:35,910 --> 00:41:33,440
that that may have shaped some of these

1056
00:41:37,670 --> 00:41:35,920
extra solar planetary systems

1057
00:41:39,430 --> 00:41:37,680
but we just have to infer it from

1058
00:41:41,190 --> 00:41:39,440
computer models and from seeing the

1059
00:41:42,950 --> 00:41:41,200
debris basically that's left over

1060
00:41:46,630 --> 00:41:42,960
afterwards

1061
00:41:50,870 --> 00:41:48,309
so my question relates to the fact that

1062
00:41:52,710 --> 00:41:50,880
you made a number of claims based on um

1063
00:41:55,670 --> 00:41:52,720
that our solar system is unique from

1064
00:41:57,990 --> 00:41:55,680
others i was curious about uniqueness uh

1065
00:41:59,910 --> 00:41:58,000
basically based on us only being able to

1066
00:42:03,270 --> 00:41:59,920
see certain types of other planets or

1067
00:42:05,349 --> 00:42:03,280
put another way um you think is our

1068
00:42:07,510 --> 00:42:05,359
research methods verifying we'll find a

1069
00:42:08,950 --> 00:42:07,520
larger percentage of solar systems like

1070
00:42:13,109 --> 00:42:08,960
our own

1071
00:42:15,109 --> 00:42:13,119
um my fear is that uh

1072
00:42:17,589 --> 00:42:15,119
we don't know enough yet

1073
00:42:19,430 --> 00:42:17,599
so we in particular

1074
00:42:21,510 --> 00:42:19,440
um so just in the last couple of years

1075
00:42:22,630 --> 00:42:21,520
we've been able to uh begin seeing

1076
00:42:24,069 --> 00:42:22,640
earth's

1077
00:42:25,750 --> 00:42:24,079
and

1078
00:42:28,309 --> 00:42:25,760
we're just now being being able to see

1079
00:42:30,230 --> 00:42:28,319
the cold giants

1080
00:42:31,990 --> 00:42:30,240
so in a few years time i hope that the

1081
00:42:34,309 --> 00:42:32,000
picture that i've given you today will

1082
00:42:36,870 --> 00:42:34,319
be still correct at least as far as the

1083
00:42:38,790 --> 00:42:36,880
close end planets but those outer ones

1084
00:42:40,790 --> 00:42:38,800
uh our knowledge is much less certain

1085
00:42:42,309 --> 00:42:40,800
and so the picture could change so for

1086
00:42:45,030 --> 00:42:42,319
example there's another method a new

1087
00:42:46,309 --> 00:42:45,040
method called microlensing when a star

1088
00:42:48,790 --> 00:42:46,319
and its planet

1089
00:42:51,109 --> 00:42:48,800
go in front of a background star the

1090
00:42:53,270 --> 00:42:51,119
background star gets lensed so the light

1091
00:42:55,430 --> 00:42:53,280
gets focused on us and it gets a little

1092
00:42:57,270 --> 00:42:55,440
bit brighter and we can see a extra

1093
00:42:58,950 --> 00:42:57,280
brightening for the planet and through

1094
00:43:01,030 --> 00:42:58,960
that method we can detect planets that

1095
00:43:02,550 --> 00:43:01,040
are further out from their star even if

1096
00:43:03,750 --> 00:43:02,560
we can only see them just that one time

1097
00:43:04,710 --> 00:43:03,760
they go in front of the background

1098
00:43:06,790 --> 00:43:04,720
object

1099
00:43:08,390 --> 00:43:06,800
and so through that method a few

1100
00:43:09,750 --> 00:43:08,400
planets have now been found that are

1101
00:43:11,510 --> 00:43:09,760
cold giants

1102
00:43:13,349 --> 00:43:11,520
so if a lot of those are found then that

1103
00:43:14,309 --> 00:43:13,359
part of the picture i've described could

1104
00:43:17,990 --> 00:43:14,319
change

1105
00:43:21,910 --> 00:43:19,349
i have a question about one of your

1106
00:43:25,430 --> 00:43:21,920
graphs you had an xy graph that showed

1107
00:43:28,150 --> 00:43:25,440
mass and size yes

1108
00:43:30,150 --> 00:43:28,160
and i just wondered you pointed out um

1109
00:43:33,270 --> 00:43:30,160
an open area in the upper left but what

1110
00:43:34,230 --> 00:43:33,280
happens at the bottom of that chart

1111
00:43:36,870 --> 00:43:34,240
um

1112
00:43:39,430 --> 00:43:36,880
there's is it because we can't visualize

1113
00:43:41,670 --> 00:43:39,440
planets that are smaller at this time

1114
00:43:43,750 --> 00:43:41,680
that's right so to give a feeling for

1115
00:43:45,670 --> 00:43:43,760
that um if the earth went in front of

1116
00:43:48,710 --> 00:43:45,680
the sun the earth is about one percent

1117
00:43:50,470 --> 00:43:48,720
of the sun's diameter so it blocks out

1118
00:43:52,309 --> 00:43:50,480
about one part in ten thousand of the

1119
00:43:54,390 --> 00:43:52,319
sun's light so you need to measure the

1120
00:43:56,550 --> 00:43:54,400
brightness of all these stars to that

1121
00:43:59,670 --> 00:43:56,560
precision in order to pick up an earth

1122
00:44:03,670 --> 00:43:59,680
and that is now possible but just barely

1123
00:44:07,190 --> 00:44:05,109
all right so over the next couple of

1124
00:44:08,710 --> 00:44:07,200
years as more more powerful telescopes

1125
00:44:10,710 --> 00:44:08,720
come online i'm assuming we'll be able

1126
00:44:12,390 --> 00:44:10,720
to see smaller objects like earth size

1127
00:44:13,190 --> 00:44:12,400
and mercury size

1128
00:44:17,430 --> 00:44:13,200
what

1129
00:44:19,510 --> 00:44:17,440
different telescopes going to enable and

1130
00:44:21,670 --> 00:44:19,520
what would that actually tell us that we

1131
00:44:23,589 --> 00:44:21,680
can't already know the with the current

1132
00:44:25,510 --> 00:44:23,599
methods

1133
00:44:28,390 --> 00:44:25,520
um

1134
00:44:30,309 --> 00:44:28,400
well it's just a matter of the size and

1135
00:44:33,030 --> 00:44:30,319
and how accurately you can measure the

1136
00:44:36,230 --> 00:44:33,040
brightness and so

1137
00:44:40,790 --> 00:44:38,470
i mean it's it's a whole new unexplored

1138
00:44:42,069 --> 00:44:40,800
territory because we really don't know

1139
00:44:46,150 --> 00:44:42,079
what

1140
00:44:47,190 --> 00:44:46,160
in that size range smaller than the

1141
00:44:48,390 --> 00:44:47,200
earth

1142
00:44:49,910 --> 00:44:48,400
and those

1143
00:44:51,670 --> 00:44:49,920
those planets tend to be just the little

1144
00:44:53,750 --> 00:44:51,680
leftover bits they're the flecks of dust

1145
00:44:56,309 --> 00:44:53,760
that get flicked around when the big

1146
00:44:57,670 --> 00:44:56,319
ones undergo any kind of special event

1147
00:44:59,349 --> 00:44:57,680
and so it's certainly possible they

1148
00:45:00,710 --> 00:44:59,359
could be very different in other systems

1149
00:45:03,109 --> 00:45:00,720
from our own

1150
00:45:07,910 --> 00:45:03,119
but we just don't know yet so it's

1151
00:45:12,470 --> 00:45:10,470
hi um my question is

1152
00:45:14,309 --> 00:45:12,480
earlier you had a graph showing

1153
00:45:18,230 --> 00:45:14,319
our solar system and how all of the

1154
00:45:20,069 --> 00:45:18,240
planets are on a flat plane yes and how

1155
00:45:22,550 --> 00:45:20,079
some of the hot jupiters were knocked

1156
00:45:25,190 --> 00:45:22,560
off of that plane by a violent event

1157
00:45:27,750 --> 00:45:25,200
is is that does that mean that most

1158
00:45:29,430 --> 00:45:27,760
solar systems will have

1159
00:45:32,230 --> 00:45:29,440
most of the material or most of the

1160
00:45:34,870 --> 00:45:32,240
planets along that flat plain

1161
00:45:35,910 --> 00:45:34,880
most of the ones we've found so far are

1162
00:45:37,270 --> 00:45:35,920
like that

1163
00:45:38,790 --> 00:45:37,280
okay

1164
00:45:40,950 --> 00:45:38,800
but again

1165
00:45:42,390 --> 00:45:40,960
our knowledge is limited so we can see

1166
00:45:43,910 --> 00:45:42,400
the planets that go in front of their

1167
00:45:45,670 --> 00:45:43,920
star

1168
00:45:47,510 --> 00:45:45,680
we can go a little bit beyond that so in

1169
00:45:49,270 --> 00:45:47,520
some cases we see a planet go in front

1170
00:45:50,309 --> 00:45:49,280
of the star but the next time it doesn't

1171
00:45:52,630 --> 00:45:50,319
go

1172
00:45:53,829 --> 00:45:52,640
in front at quite the same uh

1173
00:45:55,510 --> 00:45:53,839
quite the time we expect like it's a

1174
00:45:57,109 --> 00:45:55,520
little bit irregular a bit ahead of

1175
00:45:58,710 --> 00:45:57,119
where we expected one orbit and a bit

1176
00:46:00,790 --> 00:45:58,720
behind the next and from that we can

1177
00:46:02,069 --> 00:46:00,800
work out there must be another planet

1178
00:46:03,349 --> 00:46:02,079
and we can work out roughly where it

1179
00:46:04,870 --> 00:46:03,359
should be it's a little bit off the

1180
00:46:07,190 --> 00:46:04,880
plane so it doesn't go across the face

1181
00:46:09,510 --> 00:46:07,200
of the star we can work out how

1182
00:46:10,950 --> 00:46:09,520
massive it must be to perturb the planet

1183
00:46:12,870 --> 00:46:10,960
that we can see

1184
00:46:14,550 --> 00:46:12,880
so from from that

1185
00:46:15,910 --> 00:46:14,560
you can get an idea about how many of

1186
00:46:17,589 --> 00:46:15,920
those

1187
00:46:19,349 --> 00:46:17,599
off off-plane

1188
00:46:21,030 --> 00:46:19,359
planets there may be

1189
00:46:22,870 --> 00:46:21,040
and even when you include those it still

1190
00:46:25,829 --> 00:46:22,880
looks like the bulk of them are pretty

1191
00:46:26,950 --> 00:46:25,839
close to all lying in a plane do we do

1192
00:46:29,990 --> 00:46:26,960
we know why

1193
00:46:32,150 --> 00:46:30,000
most solar systems will form along that

1194
00:46:34,069 --> 00:46:32,160
one plane and not have a whole bunch of

1195
00:46:35,750 --> 00:46:34,079
planets that go a whole bunch of

1196
00:46:37,510 --> 00:46:35,760
different axes

1197
00:46:39,430 --> 00:46:37,520
well

1198
00:46:41,270 --> 00:46:39,440
the simplest answer is probably the best

1199
00:46:44,069 --> 00:46:41,280
there and that is that if you take that

1200
00:46:45,910 --> 00:46:44,079
cloud of dust and gas

1201
00:46:47,589 --> 00:46:45,920
it's supported by its rotation it's

1202
00:46:50,150 --> 00:46:47,599
basically in orbital motion around the

1203
00:46:52,470 --> 00:46:50,160
star so that supports it in in the

1204
00:46:54,950 --> 00:46:52,480
radial direction but in the vertical

1205
00:46:56,630 --> 00:46:54,960
direction um its rotation is not

1206
00:46:58,870 --> 00:46:56,640
supporting it it just has whatever

1207
00:47:00,630 --> 00:46:58,880
pressure it has inside the gas to stop

1208
00:47:02,470 --> 00:47:00,640
it from all collapsing to a thin sheet

1209
00:47:05,030 --> 00:47:02,480
at the middle that's why it's a disc

1210
00:47:07,190 --> 00:47:05,040
instead of a sphere it's uh it's thinner

1211
00:47:09,349 --> 00:47:07,200
in that direction along the rotation

1212
00:47:12,309 --> 00:47:09,359
axis so if the planets form from that

1213
00:47:15,030 --> 00:47:12,319
material they have to more or less share

1214
00:47:16,870 --> 00:47:15,040
the same rotation okay they can scatter

1215
00:47:18,870 --> 00:47:16,880
off each other a bit and push one up and

1216
00:47:21,910 --> 00:47:18,880
one down a bit but not very much okay

1217
00:47:26,630 --> 00:47:25,270
you had a remarkable image made by alma

1218
00:47:29,270 --> 00:47:26,640
of um

1219
00:47:30,630 --> 00:47:29,280
in the millimeter wavelengths of a

1220
00:47:32,630 --> 00:47:30,640
stellar disc

1221
00:47:35,190 --> 00:47:32,640
and i noticed a lot of uh radial

1222
00:47:38,550 --> 00:47:35,200
structure apparent is is that just an

1223
00:47:40,790 --> 00:47:38,560
artifact or is it something real do you

1224
00:47:43,829 --> 00:47:40,800
mean the uh the various rings or

1225
00:47:45,990 --> 00:47:43,839
something is the rays of radial

1226
00:47:50,150 --> 00:47:46,000
spokes coming out of it

1227
00:47:52,390 --> 00:47:50,160
well so my friends who are radio experts

1228
00:47:54,790 --> 00:47:52,400
tell me so the alma telescope

1229
00:47:58,390 --> 00:47:54,800
uh is not one big dish but instead it

1230
00:48:00,550 --> 00:47:58,400
has a few dozen smaller dishes that are

1231
00:48:01,910 --> 00:48:00,560
combined to make an image

1232
00:48:03,270 --> 00:48:01,920
and you can combine them in slightly

1233
00:48:04,870 --> 00:48:03,280
different ways like weighting

1234
00:48:07,349 --> 00:48:04,880
combinations of dishes close to the

1235
00:48:09,430 --> 00:48:07,359
center versus ones that are further out

1236
00:48:11,109 --> 00:48:09,440
and i think it's possible to make those

1237
00:48:13,030 --> 00:48:11,119
spokes go away

1238
00:48:16,150 --> 00:48:13,040
not the rings the rings stay no matter

1239
00:48:17,589 --> 00:48:16,160
what you do so we can't trust the spokes

1240
00:48:19,750 --> 00:48:17,599
yet in fact

1241
00:48:22,230 --> 00:48:19,760
people have done a thing where they they

1242
00:48:25,349 --> 00:48:22,240
try to wrap everything around

1243
00:48:28,230 --> 00:48:26,470
lay

1244
00:48:29,829 --> 00:48:28,240
the piece of the image that's at one

1245
00:48:30,790 --> 00:48:29,839
angle on the piece that's at another

1246
00:48:31,829 --> 00:48:30,800
angle

1247
00:48:33,589 --> 00:48:31,839
and

1248
00:48:35,670 --> 00:48:33,599
they cannot find any convincing evidence

1249
00:48:36,870 --> 00:48:35,680
for it not being perfectly symmetric

1250
00:48:38,150 --> 00:48:36,880
except for the fact that it's tilted

1251
00:48:39,589 --> 00:48:38,160
over a little bit

1252
00:48:42,470 --> 00:48:39,599
so as far as we can tell they're round

1253
00:48:46,549 --> 00:48:42,480
rings and nothing more good

1254
00:48:50,309 --> 00:48:48,470
hi thank you for the lecture um i have

1255
00:48:52,950 --> 00:48:50,319
two questions actually um the first

1256
00:48:57,109 --> 00:48:55,270
giving the

1257
00:49:00,150 --> 00:48:57,119
more to our solar system or

1258
00:49:01,750 --> 00:49:00,160
the missing planet theory in our solar

1259
00:49:04,549 --> 00:49:01,760
system can you shed some light on that

1260
00:49:06,950 --> 00:49:04,559
given the mass of the planet that was

1261
00:49:09,430 --> 00:49:06,960
supposedly in our solar system before it

1262
00:49:11,510 --> 00:49:09,440
escaped and the apparent position it had

1263
00:49:13,190 --> 00:49:11,520
in our solar system

1264
00:49:16,630 --> 00:49:13,200
well you could imagine a couple of

1265
00:49:17,829 --> 00:49:16,640
missing planets so one would be inside

1266
00:49:19,990 --> 00:49:17,839
mercury

1267
00:49:22,230 --> 00:49:20,000
why is there nothing there

1268
00:49:23,750 --> 00:49:22,240
and uh one answer that people have come

1269
00:49:26,630 --> 00:49:23,760
up with in that case is perhaps there

1270
00:49:28,870 --> 00:49:26,640
were some more planets inside mercury

1271
00:49:31,349 --> 00:49:28,880
and perhaps around mercury's orbit

1272
00:49:32,710 --> 00:49:31,359
but they went unstable

1273
00:49:35,349 --> 00:49:32,720
for some reason and some of them

1274
00:49:36,390 --> 00:49:35,359
collided so mercury is a bit unusual in

1275
00:49:38,470 --> 00:49:36,400
that

1276
00:49:40,790 --> 00:49:38,480
it has an enormous iron core

1277
00:49:41,990 --> 00:49:40,800
and relatively thin layer of rock on the

1278
00:49:43,349 --> 00:49:42,000
outside

1279
00:49:46,390 --> 00:49:43,359
and so perhaps what happened was some of

1280
00:49:48,630 --> 00:49:46,400
those collisions blasted off whatever uh

1281
00:49:50,069 --> 00:49:48,640
surface layers it had and it's just

1282
00:49:51,910 --> 00:49:50,079
um

1283
00:49:52,950 --> 00:49:51,920
it's just the fragment that's left at

1284
00:49:54,790 --> 00:49:52,960
the center

1285
00:49:57,030 --> 00:49:54,800
so that's that could be one explanation

1286
00:49:58,549 --> 00:49:57,040
for why there's a missing planet uh very

1287
00:50:00,870 --> 00:49:58,559
near the sun

1288
00:50:02,470 --> 00:50:00,880
as another possibility is that you could

1289
00:50:04,790 --> 00:50:02,480
say there's a missing planet in the

1290
00:50:06,630 --> 00:50:04,800
asteroid belt

1291
00:50:09,109 --> 00:50:06,640
why do we have some small fragments that

1292
00:50:11,190 --> 00:50:09,119
added up don't amount to anything even

1293
00:50:14,069 --> 00:50:11,200
close to mars

1294
00:50:15,990 --> 00:50:14,079
um and and not have another big planet

1295
00:50:17,430 --> 00:50:16,000
you could add add a planet there and not

1296
00:50:19,510 --> 00:50:17,440
much disturb the rest of the solar

1297
00:50:21,829 --> 00:50:19,520
system

1298
00:50:23,589 --> 00:50:21,839
and uh various ideas have been put

1299
00:50:25,670 --> 00:50:23,599
forward for that missing planet over the

1300
00:50:27,430 --> 00:50:25,680
years one is that

1301
00:50:30,630 --> 00:50:27,440
perhaps jupiter came inwards a little

1302
00:50:33,030 --> 00:50:30,640
bit early in the solar system's history

1303
00:50:34,549 --> 00:50:33,040
and then went back out again

1304
00:50:36,630 --> 00:50:34,559
perhaps under the influence of saturn as

1305
00:50:37,910 --> 00:50:36,640
saturn was forming if it did that it may

1306
00:50:39,430 --> 00:50:37,920
have cleared out

1307
00:50:41,349 --> 00:50:39,440
the asteroid belt region and may have

1308
00:50:43,190 --> 00:50:41,359
also contributed to mars being not that

1309
00:50:45,430 --> 00:50:43,200
big mars is only about one-tenth the

1310
00:50:47,670 --> 00:50:45,440
mass of the earth and so this is called

1311
00:50:49,670 --> 00:50:47,680
the grand tax scenario like a boat

1312
00:50:51,829 --> 00:50:49,680
tacking in and then out again so it

1313
00:50:54,549 --> 00:50:51,839
might be an explanation for another gap

1314
00:50:56,470 --> 00:50:54,559
in the solar system my second question

1315
00:50:58,549 --> 00:50:56,480
is um

1316
00:51:00,710 --> 00:50:58,559
are all jupiter-sized planets that

1317
00:51:03,670 --> 00:51:00,720
migrate in to their solar to their

1318
00:51:05,910 --> 00:51:03,680
parent star doomed or are they able to

1319
00:51:07,990 --> 00:51:05,920
theoretically stop in a position say

1320
00:51:10,470 --> 00:51:08,000
like in the goldilocks zone of earth

1321
00:51:15,510 --> 00:51:10,480
that is a good question and one that

1322
00:51:20,470 --> 00:51:17,430
because we do see some hot jupiters they

1323
00:51:23,589 --> 00:51:20,480
can't all plunge into their stars

1324
00:51:25,270 --> 00:51:23,599
and one way that they could stop is

1325
00:51:26,950 --> 00:51:25,280
perhaps in the later stages of planet

1326
00:51:29,829 --> 00:51:26,960
formation if as you come close to the

1327
00:51:32,069 --> 00:51:29,839
star there may be a gap so the gas comes

1328
00:51:32,790 --> 00:51:32,079
to an end perhaps it gets funneled onto

1329
00:51:51,829 --> 00:51:32,800
the

1330
00:51:54,150 --> 00:51:51,839
planet perhaps its migration could stop

1331
00:51:56,470 --> 00:51:54,160
at that point or near that point that's

1332
00:51:58,150 --> 00:51:56,480
one of the explanations people have

1333
00:52:01,670 --> 00:51:58,160
have put forward

1334
00:52:04,069 --> 00:52:01,680
if i could just squeak one more in um

1335
00:52:06,230 --> 00:52:04,079
have you discovered any planets around a

1336
00:52:07,750 --> 00:52:06,240
or o type stars

1337
00:52:09,270 --> 00:52:07,760
um

1338
00:52:11,109 --> 00:52:09,280
let me think so

1339
00:52:12,870 --> 00:52:11,119
i think somebody may have claimed an o

1340
00:52:15,270 --> 00:52:12,880
star but i'm not sure i believe it but

1341
00:52:16,390 --> 00:52:15,280
for a stars there are quite a few so

1342
00:52:19,589 --> 00:52:16,400
what people have done is look at

1343
00:52:20,710 --> 00:52:19,599
so-called retired a stars so a stars

1344
00:52:24,470 --> 00:52:20,720
that have gotten late enough in their

1345
00:52:26,309 --> 00:52:24,480
life so that their outer layers swell up

1346
00:52:28,309 --> 00:52:26,319
so i should fill in there so when a

1347
00:52:30,309 --> 00:52:28,319
stars are in the main part of their

1348
00:52:32,710 --> 00:52:30,319
lives just like the sun their outer

1349
00:52:35,190 --> 00:52:32,720
layers are hot enough so that most atoms

1350
00:52:36,710 --> 00:52:35,200
have lost um

1351
00:52:38,630 --> 00:52:36,720
enough electrons so that they don't

1352
00:52:40,230 --> 00:52:38,640
produce spectral lines and that means

1353
00:52:41,829 --> 00:52:40,240
that you you can't accurately measure

1354
00:52:44,230 --> 00:52:41,839
the velocity of the star towards you or

1355
00:52:45,990 --> 00:52:44,240
away from you so for the main sequence a

1356
00:52:48,230 --> 00:52:46,000
stars we don't really know whether they

1357
00:52:50,950 --> 00:52:48,240
have planets when they get older and

1358
00:52:53,109 --> 00:52:50,960
their outer layers swell up and cool off

1359
00:52:54,950 --> 00:52:53,119
they get the spectral lines back again

1360
00:52:56,549 --> 00:52:54,960
and so we can we can see the planets

1361
00:52:58,790 --> 00:52:56,559
then and so for those older stars there

1362
00:53:00,630 --> 00:52:58,800
are quite a few planets known

1363
00:53:01,990 --> 00:53:00,640
and i guess i haven't been reading up on

1364
00:53:04,150 --> 00:53:02,000
that lately but i think the last i

1365
00:53:06,870 --> 00:53:04,160
remember it looked like there were

1366
00:53:09,030 --> 00:53:06,880
um there was a deficit of planets in

1367
00:53:10,630 --> 00:53:09,040
close they started at about the earth's

1368
00:53:11,510 --> 00:53:10,640
distance from the sun

1369
00:53:12,950 --> 00:53:11,520
so

1370
00:53:14,710 --> 00:53:12,960
they seem to be a little bit different

1371
00:53:16,630 --> 00:53:14,720
than the sun-like stars in their

1372
00:53:22,549 --> 00:53:16,640
population of planets

1373
00:53:28,710 --> 00:53:25,270
hi thank you for a great talk

1374
00:53:31,349 --> 00:53:28,720
so we know that nebulae contain regions

1375
00:53:33,430 --> 00:53:31,359
of dense gas and dust

1376
00:53:35,589 --> 00:53:33,440
so one of the theories is that

1377
00:53:37,910 --> 00:53:35,599
a nearby supernova

1378
00:53:39,670 --> 00:53:37,920
releases some kind of a shock wave that

1379
00:53:42,150 --> 00:53:39,680
then bumps up against

1380
00:53:44,870 --> 00:53:42,160
that dense region of gas and dust and

1381
00:53:46,710 --> 00:53:44,880
triggering star formation

1382
00:53:48,470 --> 00:53:46,720
can you shed some light as to how that

1383
00:53:49,670 --> 00:53:48,480
happens i've thought about it a lot i'm

1384
00:53:53,270 --> 00:53:49,680
still having a little bit of a tough

1385
00:53:55,270 --> 00:53:53,280
time with the physics of how that occurs

1386
00:53:57,349 --> 00:53:55,280
well

1387
00:53:59,670 --> 00:53:57,359
seems like a couple of times a year

1388
00:54:01,190 --> 00:53:59,680
somebody claims to have observed that in

1389
00:54:03,750 --> 00:54:01,200
action

1390
00:54:05,589 --> 00:54:03,760
but it has been uh

1391
00:54:06,950 --> 00:54:05,599
it has been difficult to

1392
00:54:09,750 --> 00:54:06,960
to confirm

1393
00:54:15,190 --> 00:54:11,349
in one of these clouds it's going to

1394
00:54:19,349 --> 00:54:17,670
the outer layers can be quiescent when

1395
00:54:20,470 --> 00:54:19,359
the inner layers have already begun to

1396
00:54:22,309 --> 00:54:20,480
collapse

1397
00:54:24,470 --> 00:54:22,319
and so if we see

1398
00:54:26,309 --> 00:54:24,480
um

1399
00:54:28,470 --> 00:54:26,319
if we if we see

1400
00:54:30,549 --> 00:54:28,480
a system over which a shock wave has

1401
00:54:32,390 --> 00:54:30,559
just passed it's a little hard to know

1402
00:54:35,349 --> 00:54:32,400
if the collapse to form a star was

1403
00:54:37,030 --> 00:54:35,359
triggered by the shock wave or not

1404
00:54:38,630 --> 00:54:37,040
another another reason that that's a

1405
00:54:40,870 --> 00:54:38,640
hard problem is that we only get a

1406
00:54:43,349 --> 00:54:40,880
snapshot because the passage of the

1407
00:54:45,109 --> 00:54:43,359
shock wave can take many years many

1408
00:54:47,349 --> 00:54:45,119
astronomers lifetimes

1409
00:54:49,510 --> 00:54:47,359
and so we can't uh we can't get the

1410
00:54:50,630 --> 00:54:49,520
whole picture we just see an instant in

1411
00:54:54,069 --> 00:54:50,640
time

1412
00:54:56,630 --> 00:54:54,079
and for those reasons um

1413
00:54:59,589 --> 00:54:56,640
while it's it seems like a really

1414
00:55:01,670 --> 00:54:59,599
plausible idea and it may happen um i

1415
00:55:02,710 --> 00:55:01,680
don't think it's been very convincingly

1416
00:55:04,790 --> 00:55:02,720
shown

1417
00:55:07,430 --> 00:55:04,800
that it is happening in any one

1418
00:55:12,309 --> 00:55:07,440
particular case

1419
00:55:16,630 --> 00:55:14,870
i wanted to ask about the

1420
00:55:18,549 --> 00:55:16,640
the size of the star and what effect it

1421
00:55:20,710 --> 00:55:18,559
might have on the potential

1422
00:55:23,990 --> 00:55:20,720
planets that might form the types of

1423
00:55:29,349 --> 00:55:27,109
so the size of the star so people have

1424
00:55:30,870 --> 00:55:29,359
been searching for planets around stars

1425
00:55:32,549 --> 00:55:30,880
with a range of masses we talked just a

1426
00:55:34,710 --> 00:55:32,559
minute ago about the ones a bit more

1427
00:55:36,309 --> 00:55:34,720
massive than the sun

1428
00:55:39,670 --> 00:55:36,319
people have also looked at stars less

1429
00:55:42,630 --> 00:55:40,549
so

1430
00:55:44,309 --> 00:55:42,640
m dwarfs and even brown dwarfs and

1431
00:55:46,390 --> 00:55:44,319
there's certainly there have been

1432
00:55:48,549 --> 00:55:46,400
these disks found so disks of gas and

1433
00:55:50,309 --> 00:55:48,559
dust around the young examples many of

1434
00:55:51,510 --> 00:55:50,319
those are known

1435
00:55:53,349 --> 00:55:51,520
um

1436
00:55:54,950 --> 00:55:53,359
planets i think there are fewer but

1437
00:55:56,710 --> 00:55:54,960
there are some now

1438
00:55:59,190 --> 00:55:56,720
um

1439
00:56:02,870 --> 00:55:59,200
i think there was a a uh

1440
00:56:05,349 --> 00:56:02,880
a prediction that there should be uh

1441
00:56:06,390 --> 00:56:05,359
fewer giant planets around the smallest

1442
00:56:07,430 --> 00:56:06,400
stars

1443
00:56:09,030 --> 00:56:07,440
perhaps because you just don't have

1444
00:56:10,870 --> 00:56:09,040
enough material

1445
00:56:12,230 --> 00:56:10,880
um and i'm not sure whether that has

1446
00:56:14,150 --> 00:56:12,240
been borne out

1447
00:56:16,309 --> 00:56:14,160
in the planets that people have looked

1448
00:56:17,829 --> 00:56:16,319
for of course most people are looking

1449
00:56:19,349 --> 00:56:17,839
for earths because that feels like the

1450
00:56:21,270 --> 00:56:19,359
most exciting thing

1451
00:56:23,109 --> 00:56:21,280
and so there are fewer people looking at

1452
00:56:24,069 --> 00:56:23,119
these smaller stars and so we don't know

1453
00:56:26,150 --> 00:56:24,079
as much

1454
00:56:29,030 --> 00:56:26,160
is there a

1455
00:56:31,270 --> 00:56:29,040
tapering off maybe of the maybe larger

1456
00:56:32,630 --> 00:56:31,280
larger and larger stars compared to the

1457
00:56:34,870 --> 00:56:32,640
sun

1458
00:56:35,829 --> 00:56:34,880
um

1459
00:56:36,710 --> 00:56:35,839
so

1460
00:56:42,950 --> 00:56:36,720
for

1461
00:56:44,950 --> 00:56:42,960
and there i don't think that there are

1462
00:56:46,789 --> 00:56:44,960
significantly fewer planets but just

1463
00:56:47,910 --> 00:56:46,799
that they happen to be a little bit

1464
00:56:50,870 --> 00:56:47,920
further out

1465
00:56:54,390 --> 00:56:50,880
than for the sun-like stars

1466
00:57:01,349 --> 00:56:57,589
um how do the stars and planets from

1467
00:57:02,390 --> 00:57:01,359
other galaxies affect us

1468
00:57:03,190 --> 00:57:02,400
um

1469
00:57:07,990 --> 00:57:03,200
we

1470
00:57:09,190 --> 00:57:08,000
about the uh about the planets in other

1471
00:57:11,190 --> 00:57:09,200
galaxies

1472
00:57:12,630 --> 00:57:11,200
so

1473
00:57:14,710 --> 00:57:12,640
um

1474
00:57:17,270 --> 00:57:14,720
almost all of the planets that we know

1475
00:57:19,910 --> 00:57:17,280
of around other stars are within

1476
00:57:22,630 --> 00:57:19,920
um a couple of thousand light years of

1477
00:57:24,470 --> 00:57:22,640
us so within our region of the galaxy

1478
00:57:27,510 --> 00:57:24,480
microlensing which i mentioned earlier

1479
00:57:28,710 --> 00:57:27,520
in the question time there we can see

1480
00:57:30,230 --> 00:57:28,720
planets

1481
00:57:32,789 --> 00:57:30,240
just for a moment as they pass across a

1482
00:57:37,109 --> 00:57:32,799
distant star we can see planets that are

1483
00:57:38,789 --> 00:57:37,119
halfway to the center of our galaxy

1484
00:57:40,789 --> 00:57:38,799
but planets that are further away we

1485
00:57:42,309 --> 00:57:40,799
don't don't have a good way to detect

1486
00:57:44,630 --> 00:57:42,319
yet

1487
00:57:47,510 --> 00:57:44,640
um and i have another question

1488
00:57:50,069 --> 00:57:47,520
um how are the planets um

1489
00:57:52,549 --> 00:57:50,079
formed like are their sizes and shapes

1490
00:57:56,309 --> 00:57:52,559
formed based on the size of the star and

1491
00:57:57,430 --> 00:57:56,319
what and how what type of star it is

1492
00:57:59,349 --> 00:57:57,440
um

1493
00:58:01,190 --> 00:57:59,359
let me see if i can add anything so we

1494
00:58:02,390 --> 00:58:01,200
talked a little bit about the uh the a

1495
00:58:06,150 --> 00:58:02,400
stars

1496
00:58:07,510 --> 00:58:06,160
then the low-mass

1497
00:58:10,150 --> 00:58:07,520
ones

1498
00:58:13,430 --> 00:58:11,190
so

1499
00:58:15,109 --> 00:58:13,440
uh

1500
00:58:17,670 --> 00:58:15,119
it does seem like there there's a

1501
00:58:19,270 --> 00:58:17,680
gradient in in um

1502
00:58:20,630 --> 00:58:19,280
in

1503
00:58:23,109 --> 00:58:20,640
the size of the planets that you can

1504
00:58:24,789 --> 00:58:23,119
form and perhaps in how far out they are

1505
00:58:26,230 --> 00:58:24,799
from the star

1506
00:58:29,030 --> 00:58:26,240
i think i can add a little bit to that

1507
00:58:31,030 --> 00:58:29,040
so if we look at

1508
00:58:32,549 --> 00:58:31,040
the debris that's left over after the

1509
00:58:34,069 --> 00:58:32,559
gas has cleared

1510
00:58:38,230 --> 00:58:34,079
so

1511
00:58:40,309 --> 00:58:38,240
and comets are releasing dust all the

1512
00:58:42,150 --> 00:58:40,319
time into the solar system and so we

1513
00:58:43,030 --> 00:58:42,160
have the zodiacal light which you can

1514
00:58:45,510 --> 00:58:43,040
see

1515
00:58:48,230 --> 00:58:45,520
if you go out at a very dark sight and

1516
00:58:50,470 --> 00:58:48,240
look near the horizon just around sunset

1517
00:58:51,829 --> 00:58:50,480
or sunrise there's a little bit of dust

1518
00:58:53,670 --> 00:58:51,839
floating around

1519
00:58:56,309 --> 00:58:53,680
near the plain of the planets

1520
00:58:58,470 --> 00:58:56,319
and in some other planetary systems we

1521
00:59:00,630 --> 00:58:58,480
see that dust also

1522
00:59:03,190 --> 00:59:00,640
debris from the planets grinding and

1523
00:59:05,829 --> 00:59:03,200
asteroids grinding each other down

1524
00:59:08,150 --> 00:59:05,839
and it does seem that

1525
00:59:10,230 --> 00:59:08,160
around the lowest mass stars we don't

1526
00:59:12,390 --> 00:59:10,240
see that dust except in

1527
00:59:13,589 --> 00:59:12,400
one or two exceptional cases

1528
00:59:15,670 --> 00:59:13,599
so there may be something different

1529
00:59:16,950 --> 00:59:15,680
about the environment there so one idea

1530
00:59:19,109 --> 00:59:16,960
that has been suggested is that the

1531
00:59:20,630 --> 00:59:19,119
stellar wind the winds from those

1532
00:59:23,829 --> 00:59:20,640
low-mass stars

1533
00:59:25,430 --> 00:59:23,839
uh are able to uh to blow out the uh the

1534
00:59:26,630 --> 00:59:25,440
dust and so perhaps the dust is being

1535
00:59:28,549 --> 00:59:26,640
produced there perhaps there are still

1536
00:59:30,309 --> 00:59:28,559
planets but we don't see the dust

1537
00:59:32,549 --> 00:59:30,319
because it's been removed

1538
00:59:34,870 --> 00:59:32,559
so that's another difference between

1539
00:59:36,470 --> 00:59:34,880
in the planets around stars of different

1540
00:59:42,309 --> 00:59:36,480
sizes

1541
00:59:46,150 --> 00:59:43,910
from the internet

1542
00:59:48,549 --> 00:59:46,160
there you go sir thank you so i've been

1543
00:59:51,270 --> 00:59:48,559
given uh some questions

1544
00:59:52,150 --> 00:59:51,280
uh from social media

1545
00:59:53,109 --> 00:59:52,160
so

1546
00:59:56,309 --> 00:59:53,119
uh

1547
01:00:00,470 --> 00:59:56,319
daniel young t3 asks

1548
01:00:02,470 --> 01:00:00,480
um what types of signals or cycles can

1549
01:00:04,950 --> 01:00:02,480
we detect from exoplanets that we could

1550
01:00:07,030 --> 01:00:04,960
not detect before

1551
01:00:09,430 --> 01:00:07,040
i would like to take this in a slightly

1552
01:00:10,950 --> 01:00:09,440
different direction so

1553
01:00:13,270 --> 01:00:10,960
a signal that people have been looking

1554
01:00:15,910 --> 01:00:13,280
for is the radio signals perhaps

1555
01:00:16,789 --> 01:00:15,920
produced directly by planets

1556
01:00:19,589 --> 01:00:16,799
so

1557
01:00:21,270 --> 01:00:19,599
uh jupiter as it interacts with as its

1558
01:00:22,710 --> 01:00:21,280
magnetic field in particular interacts

1559
01:00:25,270 --> 01:00:22,720
with the solar wind

1560
01:00:26,069 --> 01:00:25,280
uh produces long wavelength

1561
01:00:27,109 --> 01:00:26,079
uh

1562
01:00:29,990 --> 01:00:27,119
radio

1563
01:00:32,150 --> 01:00:30,000
emission uh decameter wavelengths i

1564
01:00:33,190 --> 01:00:32,160
think so many yards

1565
01:00:34,789 --> 01:00:33,200
and

1566
01:00:38,390 --> 01:00:34,799
people have suggested that if you scale

1567
01:00:40,470 --> 01:00:38,400
up jupiter to uh a hot jupiter which is

1568
01:00:43,109 --> 01:00:40,480
much closer to its star so it's embedded

1569
01:00:44,549 --> 01:00:43,119
in a much stronger stellar wind and if

1570
01:00:47,030 --> 01:00:44,559
it's young may also have a stronger

1571
01:00:49,030 --> 01:00:47,040
magnetic field so it could produce a

1572
01:00:51,270 --> 01:00:49,040
really strong long wavelength radio

1573
01:00:53,670 --> 01:00:51,280
emission so there are some people here

1574
01:00:54,950 --> 01:00:53,680
at jpl working with colleagues in india

1575
01:00:56,470 --> 01:00:54,960
that have a big radio telescope that

1576
01:00:58,470 --> 01:00:56,480
have been searching for that i think

1577
01:01:00,789 --> 01:00:58,480
some people at caltech have also

1578
01:01:02,549 --> 01:01:00,799
started a search but nothing has been

1579
01:01:05,589 --> 01:01:02,559
found yet

1580
01:01:06,950 --> 01:01:05,599
so but that's an example of a signal

1581
01:01:09,589 --> 01:01:06,960
that we've been looking for and hope to

1582
01:01:13,270 --> 01:01:09,599
detect soon

1583
01:01:15,510 --> 01:01:13,280
uh also on social media ian mallett

1584
01:01:18,870 --> 01:01:15,520
asks uh could the reason that we're

1585
01:01:20,549 --> 01:01:18,880
seeing more planets near stars be

1586
01:01:22,390 --> 01:01:20,559
observational bias

1587
01:01:24,789 --> 01:01:22,400
absolutely it's

1588
01:01:26,710 --> 01:01:24,799
almost all observational bias not

1589
01:01:28,309 --> 01:01:26,720
entirely because we've seen kinds of

1590
01:01:31,270 --> 01:01:28,319
planetary systems that

1591
01:01:32,630 --> 01:01:31,280
we just don't have uh in our own case so

1592
01:01:34,150 --> 01:01:32,640
that that is certainly telling us

1593
01:01:36,549 --> 01:01:34,160
something completely new

1594
01:01:38,950 --> 01:01:36,559
but one of the of the problems that we

1595
01:01:40,870 --> 01:01:38,960
face is not fooling ourselves not

1596
01:01:42,710 --> 01:01:40,880
thinking that all that we've seen so far

1597
01:01:43,990 --> 01:01:42,720
is all that there is because there's a

1598
01:01:45,990 --> 01:01:44,000
lot more out there there's a lot more

1599
01:01:47,990 --> 01:01:46,000
further from the stars that we

1600
01:01:49,670 --> 01:01:48,000
haven't seen and won't be able to see

1601
01:01:51,109 --> 01:01:49,680
perhaps until they've done at least one

1602
01:01:53,270 --> 01:01:51,119
orbit i mean saturn's orbital period is

1603
01:01:55,349 --> 01:01:53,280
30 years so we might have to wait that

1604
01:01:57,670 --> 01:01:55,359
long to see a saturn using the radial

1605
01:01:59,430 --> 01:01:57,680
velocity method so people who haven't

1606
01:02:00,230 --> 01:01:59,440
been haven't even been looking for that

1607
01:02:02,549 --> 01:02:00,240
long

1608
01:02:04,710 --> 01:02:02,559
so there is a lot more to be discovered

1609
01:02:07,510 --> 01:02:04,720
and that i hope will be discovered

1610
01:02:08,950 --> 01:02:07,520
in the coming years

1611
01:02:10,950 --> 01:02:08,960
and then a third

1612
01:02:12,549 --> 01:02:10,960
question from social media prometheus

1613
01:02:15,030 --> 01:02:12,559
256

1614
01:02:16,390 --> 01:02:15,040
asks how would we detect planets around

1615
01:02:19,589 --> 01:02:16,400
a far-flung

1616
01:02:21,829 --> 01:02:19,599
identical copy of our solar system

1617
01:02:24,309 --> 01:02:21,839
would our planets need to be detected

1618
01:02:28,150 --> 01:02:24,319
using the transit method

1619
01:02:31,430 --> 01:02:29,510
on the whole

1620
01:02:33,270 --> 01:02:31,440
yes and

1621
01:02:34,630 --> 01:02:33,280
so jupiter you could probably detect by

1622
01:02:35,990 --> 01:02:34,640
the radial velocity method if you're

1623
01:02:38,470 --> 01:02:36,000
willing to wait

1624
01:02:42,950 --> 01:02:38,480
one orbit or maybe two to be sure so 12

1625
01:02:45,750 --> 01:02:44,950
the other planets would be really tough

1626
01:02:48,309 --> 01:02:45,760
but

1627
01:02:50,069 --> 01:02:48,319
if they transited then you could detect

1628
01:02:51,349 --> 01:02:50,079
them if you had technology similar to

1629
01:02:53,670 --> 01:02:51,359
ours

1630
01:02:58,630 --> 01:02:56,710
you'd have to be lucky again because

1631
01:03:00,710 --> 01:02:58,640
our solar system is not compact like

1632
01:03:02,950 --> 01:03:00,720
those others it's quite spread out

1633
01:03:04,470 --> 01:03:02,960
so if you have a planet very close to

1634
01:03:05,670 --> 01:03:04,480
its star you have a decent chance if it

1635
01:03:07,750 --> 01:03:05,680
has a random orientation you have a

1636
01:03:09,829 --> 01:03:07,760
decent chance that it'll be along your

1637
01:03:11,670 --> 01:03:09,839
line of sight but if it's very far away

1638
01:03:13,190 --> 01:03:11,680
there's many more possibilities for its

1639
01:03:15,270 --> 01:03:13,200
orientation and you have to be much

1640
01:03:17,430 --> 01:03:15,280
there's a much smaller probability if

1641
01:03:19,829 --> 01:03:17,440
things are random that you will get it

1642
01:03:21,510 --> 01:03:19,839
along your line of sight exactly so for

1643
01:03:24,390 --> 01:03:21,520
somebody to see

1644
01:03:25,990 --> 01:03:24,400
our jupiter from a nearby star is much

1645
01:03:27,190 --> 01:03:26,000
less likely than for us to see a hot

1646
01:03:28,789 --> 01:03:27,200
jupiter

1647
01:03:30,390 --> 01:03:28,799
so

1648
01:03:32,069 --> 01:03:30,400
there's only a small number of aliens

1649
01:03:38,390 --> 01:03:32,079
looking at our solar system and seeing

1650
01:03:43,910 --> 01:03:40,870
so um i think

1651
01:03:45,349 --> 01:03:43,920
that's all i have from social media so

1652
01:03:46,789 --> 01:03:45,359
but i'm i'm

1653
01:03:48,630 --> 01:03:46,799
still got energy and rearing to go so

1654
01:03:50,230 --> 01:03:48,640
i'm happy to take more questions

1655
01:03:51,430 --> 01:03:50,240
if people have them

1656
01:03:52,710 --> 01:03:51,440
so