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[Music]

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[Applause]

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I realized after submitting this

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abstract this is a pretty difficult room

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to tell something they don't know about

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ice I'm going to tell you some things

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I've been surprised to find out about

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ice shells and environmental

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considerations so this is work I've done

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in support of two different projects one

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is a JPL lead study called CRO which is

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looking at full mission architectures

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for accessing ice shell interiors and

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we're hoping to share the first results

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of that a TPS CDP s and a GU this fall

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so something to look forward to a quick

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plug there's going to be a session I'm

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Co convening not dissimilar to this one

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if the AG you fall meeting so if you

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think you have updates and you can

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already project them and put them in an

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abstract and submit it um might be a

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nice chance to meet in the other the

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other work they are that I've been

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supporting is honeybees slush proposal

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in sesame so I've listed a few

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co-authors here but really I've worked

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with probably 45 people between these

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so there's all the usual suspects this

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is something I stole out of a slush

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abstract or poster and it's tiny but you

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all know what these are others there's

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diurnal II activated cracks and deep

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faults and the potential for geologic

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stresses and lakes and salt lenses and

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acids and all the fun stuff and so I've

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said about trying to take a lot of these

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different abstract ideas to simplify

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them as much as possible and really look

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at how you can start to place system

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level capability constraints on them but

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yeah I noticed this when I uploaded my

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talk it's going to take forever for any

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animation to happen so I'll start by

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mentioning what's about to show up is

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Erin Leonard's geologic map I hope

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thinking about the the biggest tectonic

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worries when you go somewhere I'm only

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going to talk about your open this talk

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because it's 11 minutes and there's way

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too much to talk about in icy satellites

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but one result of Erin's work mapping

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Europa and thinking about the geologic

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history has been that the geologic

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evolution has changed over time

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she found that in Europa's earliest

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period so that's the first period down

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here at the bottom

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on the x-axis so the today is this third

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period on the x-axis you have all the

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different kinds of units and what she

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found is that if you look at the blue

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the very first thing to form on Europa

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were global regional Plains so large

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scale deformation everywhere and that

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transition to bands which are still

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large but more local features his

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transition to chaos which are relatively

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local and also cracks and craters so the

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the geology has really changed from

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widely distributed high stress

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requirement tectonics the more locally

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distributed cracks that can form at

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lower stresses and so I just had a paper

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out in Icarus where I look at sort of

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the stresses and forces available on

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Europa to deform it today and my primary

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anxieties for drilling through an ice

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shell lie in diurnal active cracks and

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I'm not as worried about deep interior

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faults so the most impressive thing I do

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are these movies of ice shells and so of

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course I'm going to show them in every

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talk I give this is showing an ice shell

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falling out from 50 kilometers to a

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present-day

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ice shell thickness for an estimate of

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interior silicate heat generation and

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internal tidal heating and on the left

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the red stuff is stiff and the blue

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stuff is convecting and in the middle

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and tracking the historical freezing

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rate which relates to salt composition

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and on the right is the age that the ice

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froze in just one quick thing I want to

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mention here is that when you actually

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simulate convection on top of an ocean

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with fully temperature dependent

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parameters it can look much different

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than the convection models you're used

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to especially because the stagnant lids

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above convection cells can be much

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higher proportion of the ice shell that

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means that you're going to be in colder

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stiffer ice for longer with the

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potential for fracture porosity and

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spend less time in the convecting regime

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near the melting temperature and so if

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you plot I took bar and showmen out of

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the europa book and you often see this

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parameterization of the convective ice

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shell thermal structure the black line

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if you plot what convective ice shell

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thermal structures might look like

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they're much closer to something like a

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conductive show there are regimes where

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I can freeze out ice shells

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to steady-state modern values and one

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thing to mention here is that all of

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this purple stuff are areas where there

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is entrained partial melt that doesn't

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immediately drain out and so you can

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find regimes where you have a slushy ice

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ocean interface if you're thinking about

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getting all the way into the water you

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might have difficulty detecting a sharp

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boundary at the ice ocean interface and

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when you get there it might not be

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mechanically intact um another issue

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with conductive shells so this is really

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difficult to see but on the y-axis is

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depth through a 15 kilometer shell and

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on the x-axis is porosity so I built a

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shell with 20% initial porosity and then

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I let it bake for a thousand years up to

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65 million years which is the current

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surface age of Europa one thing you

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notice that even if you pick a really

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high starting porosity you tend to

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maintain high porosity in about the

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upper half of a conductive ice shell so

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the issue here is I don't know what

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porosity Yorubas ice shell froze at but

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it sure is fractured in a fracture

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porosity is relatively high and has been

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throughout its history it can be

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retained over geologic time so porosity

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is more than about five percent are

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going to keep you connected to the

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vacuum and those might not just be a

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surface problem these high porosity

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could extend to depth and persist over

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geologic time so you might have

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if I make a relationship between salt

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content and an ice shell and it's

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freezing rate you can see all these

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weird structures start to form when you

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begin to make ice shells it's because

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you start to get a small wave length

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compositional convection from salts in

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addition to the thermal convection in

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the ice and what this can actually do is

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it can produce lateral and horizontal

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heterogeneity s and salt content they

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could build salt hazards into different

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parts of the ice shell that would be

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difficult to detect through remote

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sensing which could average over these

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lengths so one interesting thing to

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think about is if you assume the ocean

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is an earth so

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the ice shell on average has to be that

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salinity or less and so it's possible

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that you're going to encounter some

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where we are up to 25 kilograms of salt

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for every meter that you drill so if you

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have a 50 centimeter wide probe that's a

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couple centimeters of salt for every

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meter and so if you start to pick the

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the geologic object of interest to you

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if it's a hundred meters tall a lake or

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something that you want to freeze out

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then you could be talking several meters

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of salt lenses that you would have to

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cut through and the reason I make that

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comparison is I get asked a lot what

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happens if you hit a meteorite or

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something and I wanted to compare the

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amount of antigenic non ice material to

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potential exogenic nice material so one

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way to back at the envelope that is you

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can take this Alvarado study from 2008

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where they simulate a bunch of I'm gonna

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start with stuff from IO so they

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simulate impacts on IO and how Iowa

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ejected might end up on Europa they look

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at the distribution of Io material on

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the surface and find that there's a

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dependence on both latitude and

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longitude of that material distribution

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and so something I've done is you can

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build probability maps of where IO

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materials going to land so this is

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yellow is more likely to have material

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deposited on it and blue is not so there

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can be latitudinal and longitudinal

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dependencies in the amount of non ice

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material you might have to drill through

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and you can look at total fluxes from

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IOT Europa and start to think about how

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much over 65 million years you could

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accumulate so for example if you have a

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50 centimeter diameter drill because you

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want to stick a nuclear reactor or

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something in it you only have to deal

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with about 10 kilograms of non ice

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material every kilometer you drill if

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you're going with a finless RTG or

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stripping out your GPA chess breaks from

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the RTG you can get thinner and you have

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to deal with less material even if you

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include primary impacts on Europa from

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other bodies these numbers are still

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extremely small about a thousandth of

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what you have to worry about with salt

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and so one fun thing is you can think

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about what happens if every projectile

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that hits Europa is broken up into the

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worst size pieces so pieces on the scale

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of your drill that's not how the

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universe works but even if it were in

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that worst case you only have about a 1%

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chance for a 10 centimeter borehole of

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hitting an object that is the same size

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as your drill or bigger and you only

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have about a point six percent chance if

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it's 50 centimeters and of course in a

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reality you tend to create many many

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more small objects on an impact than you

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retain large objects and so this is

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going to skew further to the left and I

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think the chances of really having to

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worry about more than just the

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occasional dust in the ice from exogenic

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material is pretty low so for me the the

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primary things the our driving system

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capability definition is I really worry

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about title shear stresses especially on

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tethers I think Kate and her team are

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doing great work looking at how diurnal

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flexing of real tethers might cause them

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to break if the ice shell was formed

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with significant fracture porosity it

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could have retained that porosity and

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that means you can remain connected to

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the vacuum for significant depths so you

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might not just have to build pressure

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caps near the surface you might have to

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build them the whole way and it may be

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that only a small proportion of the ice

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shell is convecting especially if you're

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aiming for a 15 kilometer ice shell

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there's probably very little ductile

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portion there's very poor constraints on

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composition in general including how and

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where salt is distributed and so trying

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to think about the physical processes

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that drive that which is something a lot

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of people in this room do is extremely

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useful for planning purposes in that

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really the dangers from exogenic nice

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Arda nice material are pretty trivial

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compared to the amount of soluble not

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ice material you're going to have to

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deal with as you go through an Ice Show

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and among the many other things I don't

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have time to talk about there's the

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potential for sublimating salt lags on

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the surface that you're going to have to

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break through clathrates if they're

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stable in your opus ice shell could be a

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large problem they're a large problem in

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terrestrial drilling and also small

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scale variations in your melt jacket

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volume if you have small changes in the

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or in the volume of your mail jacket or

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the amount of heat you're putting into

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or out of your drill you can result in

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perturbations in the volume of that

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cavity and if you're in the elastic part

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of the ice you can have significant

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instantaneous pressure changes that

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could fracture ice it could force your

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melt jacket outwards into the ice or if

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you under pressure you can destabilize

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that melt cavity and so these are the

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things I'm worried about

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you're free to worry about other things