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[Music]

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[Applause]

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thanks Morgan

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it's great to be here and it's great to

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follow Marc's talk which I introduced

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some geophysical concepts for things

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that we still have yet to figure out

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about Enceladus so what I'm going to

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tell you about is a work-in-progress is

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a JPL supported study it's also

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leveraging support from the NASA

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Astrobiology Institute namely the icy

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worlds program and the idea is to we'll

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get distributed geophysical measurements

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either combination of orbiter and Lander

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or network of Landers to answer

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questions about being habitability of

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Enceladus so I'd like to not name all of

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my authors but just emphasize that

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they're people from all over the US and

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and also in France and the Czech

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Republic and I'll mention work by these

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folks so study goals again assess needed

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geophysical measurements for

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habitability as part of future searches

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for life on Enceladus and yeah so to

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summarize yeah the orbital either an

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orbital only so single or multiple

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spacecraft is would that be sufficient

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to enter the main geophysical questions

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would we need a if we land would have

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single Lander be enough would we need a

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network or perhaps some cooperation

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between them so these are just examples

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of concepts that have been studied this

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one was for Europa the graphic was

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convenient just suffice it to say there

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are ideas for Landers for in Celicas as

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well I'll also point out this is a

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modified graphic from a NASA artwork

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that was part of a press release I

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modified it to emphasize that we now

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understand that the ice is thinner at

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the poles of Enceladus so we'd like to

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understand why that is it's just one of

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the questions we want to understand so

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let me just try to motivate the

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connection between geophysics and

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habitability a little bit this isn't my

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real my main soapbox in the last few

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years so here's a nice figure from a

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work that's been prepped by one of our

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team members and a Lobo a grad student

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at Caltech working with Andy Thompson so

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the insight here because of this ice

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thickness variation infer from Cassini

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measurements Chadha as part of our group

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as well the work by Hemingway agrees

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well it has a little more interpretation

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of the gravity data so this implies a

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lateral transport because where the ice

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is thin

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you should have melting and that should

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lead to refreezing

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and where the ice is thicker and so yeah

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you have meltwater traveling along the

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ice so if there's if the ocean is salty

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at all the lateral transport implies an

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overturning convection and so we want to

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understand how that works

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and how that factors into any geothermal

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transport namely if there are

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hydrothermal plumes at the base of

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Enceladus

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or as scales Roble has studied

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distributed sorry

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throughout the the body of Enceladus so

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that's that's one thing that we're

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working on that couples in with

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determine the transport properties the

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ocean couples in with more general

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geophysical work including working with

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Gail Schilling and Gabriel Toby the kind

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of thing that was nicely explored in

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this 1d model by Melvin and pre-amp

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realloc and now is been worked by

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postdoc working with me Mohit Mel

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juanita swanee also point out that

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there's a nice talk tomorrow about be

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organics in Enceladus in the prebiotic

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chemistry session at 11 o'clock by Frank

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host Berg ok so this is the background

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for our study so what we've done this is

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sort of a small science definition team

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kind of study so we tried to identify

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all of the questions that you would want

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to look at and in order to connect

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geophysical measurements habitability so

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just running through them very quickly

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what's the distribution distribution of

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tidal heat what's why is there a

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difference between the North Pole in the

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South Pole where is the high temperature

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water rock interaction happening we do

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have evidence for high temperature water

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rock interaction is it all at the South

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Pole

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and then what's the mass exchange as I

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mentioned earlier where the rate of

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delivery of oxidants to the ocean and

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also how does the ice fraction Nate the

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materials that are coming out of the

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plume and lastly what is the nature of

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the ocean transport so we can glibly

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summarize those with these convenient

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markers at the bottom that correspond to

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the numbers and so I'll refer to those

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as I run through some measurements that

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would one one would want to make

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so I can point out that Europa clipper

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has an ice penetrating radar I think

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this is going to revolutionize our

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understanding of ice geo dynamics it

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would be great to take something like

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that to Enceladus we could think of

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stepping up that and if we have

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crossover measurements from an orbiter

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we could actually do synthetic aperture

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radar mapping and that would allow us to

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see where motion is actually happening

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so there are different methods of doing

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that there's traditional radar method

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methods there's also a light detection

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and ranging which I expect would be

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lower energy but don't quote me on that

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and those have corresponding levels of

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precision which we can map in our study

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and that would be something on our

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orbiter mm-hmm similarly we want to

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improve on the thermal measurements that

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Cassini did so these are examples of

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measurements from from Cassini across

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the tiger stripes at one particular

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tiger stripe here and from a few in his

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larger image and so we want to improve

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on that hopefully the elf study that I

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referred to earlier states a range of

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spatial resolution sensitivity that we

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would want for that kind of measurement

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so electromagnetic sounding this is

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going to be a crucial measurement for

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the Europa clipper namely by taking

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advantage of the tilted dipole magnetic

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field of Jupiter to look at the induced

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response of Europa Saturn's magnetic

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field is somewhat inconveniently

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directly aligned with its rotation and

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so that is not something that we can

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utilize however the the orbit of

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Enceladus as Mark explored it's somewhat

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eccentric because that provides a way to

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measure variations also we might use

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external oscillations in the field

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itself so that is although the of the

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Saturn's field is not tilted and so it's

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not varying due to its rotation it might

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vary intrinsically just because of

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variations within Saturn itself and

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let's see so that's something we could

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employ on a lander even although a

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single Lander would probably only be

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able to get the to infer the thickness

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of the ocean and the salinity not be

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variation in thickness or changes in

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salinity if any exists okay so we've

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done a little bit more work on gravity

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the

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with our team members who are in Prague

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also working with our team members in

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France and so that charecters is a lead

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author on some of those Murray Ben

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koba's and others they have a few papers

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recently on the distribution of tides

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and Enceladus including taking advantage

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of our knowledge of the topography of

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Enceladus as ice so here I'm showing two

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different model runs that they did for

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us one with with no deformation in the

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in the rocky part of Enceladus and

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another accounting for that deformation

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you can see they're different and and

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this is also accounting for the

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topography at the at the South Pole so

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these are the kinds of variations in

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gravity that we could measure with an

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orbiter the orbiter would have to go

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very slow so less than 2.2 kilometers

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per second at an altitude of hundred

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kilometers and so that's not something

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you could achieve with the multiple

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flyby mission so you can't envision

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orbiting Saturn and flying buy and sell

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it it's like for example like we're

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doing with your OPA clipper around

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Jupiter not around Saturn so you could

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also do gravity from a lander it might

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be it would be beneficial to have

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multiple vendors in that case another

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thing you can do that's related to

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gravity from the same model runs that I

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showed you previously

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you can also compute how much the

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surface of evidence' lattice is flexing

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it's tilting you would sense that if you

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were on the surface as a slight tilt if

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you looked up at the stars you would see

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they're moving a little bit that motion

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that turns out is on the order of 2

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micro radians so it's very small that's

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the kind of thing you wouldn't be able

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to see if you were orbiting Enceladus

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but you would be able to sense that with

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a dedicated instrument or even a

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seismometer on the surface of Enceladus

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so moving on to seismology we've done a

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lot of work on this thanks to a previous

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study that we went through for the last

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three years previous three years so I

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will assert that this is the best

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technique for resolving the interior

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structure is the only way you're going

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to sense the detail composition of the

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deeper rocky interior I think in a

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categorical way and I can I can

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emphasize that you would have that

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information even more supported if you

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were able to separate your seismic

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interpretation

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based on gravity measurements and a

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medic field measurements so a single

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seismometer as is being employed on the

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insight mission on Europa could detect

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signals generated anywhere within

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Enceladus there's a Mars I said in

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Soledad Europa okay too many too many

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planets just to talk about pardon me

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pardon me

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now you don't usually say Mars that

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often which is it which is a drawback of

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mine it's not another criticism of Mars

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so right and so since we know there's

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observed plume activity that itself is a

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seismic source that we could utilize and

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there are analogies in the form of

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geysers on earth and volcanic tremor

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that might allow us to predict what

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those would look like seismically of

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course multiple seismometers could

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reveal the mechanics of those fissures

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or in general be much more helpful for

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mapping activity inside of Enceladus

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I should explain this complicated graph

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if you've taken an introductory

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seismology class you would see something

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like this extending over an hour rather

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than 300 seconds I'm sorry the top is

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cut off it's just showing the

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propagation of different waves the

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transverse the the radial and the

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azimuthal components of the waves are

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the different colors over a period of

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time and as a function of distance all

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the way from the source to halfway

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around Enceladus so it's just it's just

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showing that you can see reflections

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these are these different kind of

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scattered features over here on the

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right are reflections from different

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boundaries including the bottom of the

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ice shell and the bottom of the ocean

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and so we can do this kind of modeling

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in the forward modeling fashion thanks

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to modern computational technology in

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fact based on radial structure models

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that I've come up with combined with

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that topography and ice thickness that I

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mentioned earlier we can create detailed

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models Enceladus either either asserting

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radial symmetry or taking into account

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the variations and then we can do those

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full wave form models so we've another

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postdoc working with us at JPL using

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salvus a program that's being developed

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so I'll show you an animation this is

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this this graphic is showing

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specifically the case where you don't

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have where you have you're not ready

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you're not sterically symmetric so the

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ice shells varying in thickness and also

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in topography

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so in the movie that you'll see on the

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left the comparison of the spherically

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symmetric case so you can see the source

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from the South Pole just read just

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reverberating to the North Pole and back

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and this is accounting for propagating

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modes in the in the deeper interior as

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well it's much more complicated and

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chaotic

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if you account for the actual features

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of Enceladus so there's more work to do

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and we're doing that work so just

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wrapping it up then a single orbiter

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could certainly advance our

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understanding themselveses interior

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including the heat and composition and

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the workings of the ice turns out you

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that the the some of the requirements

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for those gravity measurements would

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would only be achieved if you had some

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kind of surface device as well it could

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be just a mirror but this is this is

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pointing to the benefits of having a

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combined lander orbiter mission of

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course a network of Landers would be

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helpful you can a single Lander give us

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some really interesting information I

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think the best outcome would be to

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combine all of those things and in a

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future version its presentation and the

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paper that will follow I look forward to

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sharing more rigorous studies of the

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cost and other things that the factor

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and prioritizing among those so thank