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yeah so I can be talking about large

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captured satellites and that natural

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satellites exomoons and just briefly

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we've talked a lot about Kepler in this

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session and these are the all the

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results as of the last double a s so far

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and you can see there are tons of

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planets they're getting but they cannot

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you know when we get out here in the

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habitable zone they start to get fewer

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and fewer because you get fewer and

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fewer transits it's harder to detect so

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most of the planets we actually know

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about that are out in this region you

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know it's similar temperatures to earth

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are much larger than Earth they're giant

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planets and really didn't expect this

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but you know ten years ago people said

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you're crazy if you thought there are so

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many giant planets out here but there

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are tons of them there aren't there

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aren't the majority of planets in there

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but there are lots of them there and we

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know that they're there so you know

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potentially you know if you want to try

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and find habitable places this sounds

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like a good place to start especially is

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you know if they're big enough they

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might have satellites that are large

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enough to be habitable in order to be

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handle on the surface you need to be at

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least somewhat new as a large desert you

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know Mars astronomer somewhat is large

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so you know with an order of magnitude

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to the size of Earth is what we're

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talking about here but that's still

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pretty hard for the satellites in our

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solar system so you need something quite

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large to do that but if you look at the

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natural satellites in our solar system

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the largest one is Ganymede it's just a

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little bit larger than mercury and which

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means is quite smaller than Earth the

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only one of them actually even has an

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atmosphere is Titan and that's because

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it's so cold at time wouldn't keep its

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atmosphere if you were as close to the

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Sun as Earth is simply because they just

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get too hot and the it would escape away

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pretty fast so it's really hard to have

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a large satellite close into

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a star it's just it gets they the the

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dynamics of how it creats around the the

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planet just make it so that you know

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you're not going to get you know

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naturally forming satellites around the

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planet that are much larger than

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Ganymede even if you have a much larger

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joint plan to start out with so it sort

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of tricky to get you know much better

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than this unless you start to look at

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other means of having satellites and

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bright yellow you say regular satellites

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these are satellites are formed from the

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from a sir compliant airy disk you know

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like like the disk around the stars

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begin with but it's around the planet

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and they form a little miniature solar

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system irregular satellites are objects

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that form somewhere else somewhere else

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is usually for the giant planets meaning

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on the Kuiper belt region but it also

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mean asteroids as well which come in and

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then afterwards get captured and

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afterwards is still a long time ago you

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know solar system wise but it was still

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much after all the planets and

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everything had formed and then as things

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were so dynamically evening evening out

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these captures happen we've only been to

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one of these irregular satellites and

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that's Phoebe because they tend to be in

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very wide orbits very you know serve it

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you know eccentric at the edges sort of

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thing and that's how we can tell that

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they're they've obviously been captured

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because you have to have been captured

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to be there there are probably much

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closer in satellites but they were also

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captured we just can't tell who they're

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captured because they've sort of evened

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out and one of the ones that's evened

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out quite a bit but it's still obviously

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a capture is neb is frightening now most

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capture satellites are very small this

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is the largest of the Saturnian capture

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satellites and this is only a couple

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hundred kilometers across where is this

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guy here is about the size of our moon

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so it's about 3,000 kilometers or

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and it's the only large satellite of

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Neptune all the other Giants sell

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although other giant planets have

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certain nice little systems of this is

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Jupiter Saturn yours all of these nice

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systems of regular satellites don't have

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that on Neptune Neptune you just have

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Triton and a few very very small guys so

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and Trident is in this retrograde

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backwards orbit so the only story that

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makes sense here is that you used to

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have a regular satellite system and then

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something happens such that Triton came

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through bulldozer threw away all of

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those regular satellites and that were

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much smaller than it and you had and you

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know did just left itself and you know

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in that way you end up sort of trading

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up because you start out with a much

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much smaller satellites and end up with

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something that's quite a bit larger you

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know we thankfully we have actually been

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to train this is a bit of a synthetic

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image but you can actually see these all

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streaks on there those are actually

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little plumes of nitrogen they're

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trailing up dust onto the surface this

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is an active dynamic surface out of the

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all right kidney hear me okay so what we

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think probably happened to cause this

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this capture event was that giant

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planets migrate and if you've not been

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following planetary science this is the

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most revolutionary thing that has

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happened in solar system science in the

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past ten years is this realization that

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the giant planets are in many cases

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nowhere near where they were when they

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actually originally formed and we used

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to we used to map out with the the

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protoplanetary disk was like we just

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kind of assumed all the planets where

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they were and then we just saw spread

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out that material and said okay it's a

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disk reality they're much more compact

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we had a much more massive disk so

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they're all very close in and in Neptune

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actually probably was inside of Uranus

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and then Jupiter and Saturn gun to me

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motion residents with each other they

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kind of moved it around a little bit you

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can see there but they really moved

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around the smaller of the two giants and

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so Neptune's swiftness and went out into

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this big disk of material which is the

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you know the prototype er belt and

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dissipated most of it and in the process

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of dissipating it encounter a lot of

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things and one of those that encountered

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was frightened it's probably the largest

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thing it actually had a close encounter

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with and trying got captured and

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bulldozer delay all of the original

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satellites of Uranus and just left

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itself so how supposed to be a picture

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their butts condo never mind so you know

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planets migrate and this migration

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happens both ways in our solar system it

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happened in outward motion with you know

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missions like Kepler we're starting to

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get all the all the migrations that have

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not in word so this can go in both

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directions and the drawing plans come in

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that can go out and and one there when

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they're migrating they aren't counting

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lots of objects that were there

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previously and you can have these

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captures occur but to have a capture

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you need to it's a angular momentum

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switch right is if you're coming in and

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it you know at a hyperbolic orbit when

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you're approaching a planet you're going

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at least parabolic if not hyperbolic you

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have as much energy going out as you

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came in with if nothing happens so what

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you need is some sort of an event when

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you're close to the planet which causes

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you to lose a little bit of energy and

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trade angular momentum with the system

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and the two two ways you can do this one

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is that you already have a satellite and

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you get rid of it along the way so this

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is what the method that is our most

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commonly you know given for the capture

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of Triton is he you have Trident and

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then you have maybe a satellite and it

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comes in close comes in close and you

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know the motion of the two objects

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themselves together is hyperbolic but

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then when they get close here one's

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going a little bit faster than I

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prologue and one's going a little bit

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slower so then right at closest approach

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you kick off one of them and it goes off

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really fast and the other guy is going

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but much slower and it gets captured

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into the elliptical orbit around here so

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that's a really clean it's a very neat

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way of doing it unfortunately you also

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you have to presuppose that you have a

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satellite on there which makes it a lot

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more complicated then cuz it's a

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two-stage process the other way to do

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that is to say that you already have a

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satellite around the giant planet which

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you know makes sense because all the

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giant planets have many satellites and

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then and you actually swap places with

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it with that now it's a much smaller

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cross-section to do this you need to be

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just or just just right to get in there

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but you know do you have much more

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satellites to work with so potentially

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is a much more effective method so oh so

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that so this is a case here where you're

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coming in and so the squigglies there

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are

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the small satellite around one of the

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the large objects the red object and

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then you got the blue here which is the

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other large object and they get close

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here and then this small guy absorbs

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most of the momentum of the system gets

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and just gets tossed out of there at

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like 10 kilometers a second it's just

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zooming out and so it's taking away all

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this momentum and they get trapped in

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into a nice elliptical orbit around each

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other and you let that go long enough

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and they'll actually circularize just

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something that's nice and stable so I

242
00:11:06,819 --> 00:11:03,230
meant to do a bunch of simulations that

243
00:11:09,009 --> 00:11:06,829
for various reasons it didn't happen but

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simulations that I've done so far mainly

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with this first method and those what

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they re student some for last where we

247
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were just sort of taking making

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synthetic systems where you had a earth

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and a moon or earth with a moon that's

250
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the size of Mars or Mars with the moon

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that's the size of our moon and just

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kind of toss that at a giant planet and

253
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see if the captures or not and you know

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in general we were getting so captures

255
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maybe sir ten five percent of the time

256
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and some you know depending on the

257
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circus is up to twenty percent of the

258
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time so you know it's it's not that it

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happens every time there's a close

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encounter but it's not incredibly rare

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either now of course you can see here

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the most common outcome for most of

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these was that there was an impact so

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that your most common case the large one

265
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impacts or maybe the smaller win impacts

266
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but the red line there is the actual

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capture event and it it does happen is

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more likely in these cases that the

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larger of the two captures it's good and

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then we've all you know that when they

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capture they always capture in two very

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eccentric orbits but they don't stay

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that way because eccentric orbits are

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not stable when you're near something so

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their body tied circular isaam pretty

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fast and they circle eyes and they're

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tidally locked they are we talking about

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tightly lock a lot today but they're

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tightly locked to the planet and they

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tend to be in orbits that are a couple

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days so you know as far as lumination is

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concerned you know the they're seeing

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the Sun just

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often as they would if they were you

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know in a 24-day rotation period at 1a

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you and in fact if you were on the far

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side of one of these exomoons you'd

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never know that you're in orbit around a

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so they get you know about fifty percent

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of them then it have captured our serve

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you know circular as well and they get

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and the circularization happens fast

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this happens in about a million years so

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they get a lot of heat they're like I oh

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very briefly they get a lot of heat you

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know in this pulse but they're also

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bulldozing away all the other moons IO

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has heating there because it's

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interacting with the other satellites in

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the solar system peter system if Triton

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doesn't have that and we're really

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looking at cases more like Triton words

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bulldozing away everything else and

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you're just left without with that one

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so you're not gonna have long term tidal

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heating in these there any heating

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interior is going to be radiogenic long

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live stuff and finally are they

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detectable probably but you need a lot

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of transits to tell the first few

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transits they're just gonna be off a

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little bit and it's going to look like

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noise in the data you lots and lots of

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transits to tell and it's only the

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furthest most of the exoplanets that we

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can actually do this for so 7 plus

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transits for something as a 1a you

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around a solar type star that takes

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seven years it's going to take a little

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while before we start to get these XM

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ones because we just need lots and lots

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of transits and so just wrapping it up

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exit wounds are potentially large enough

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to be habitable the ones that are

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potentially habitable are the easiest to

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detect so if we hear about any exit

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wounds within the next 10 years they're

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going to be ones we want to look at for

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habitability you know to capture these

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there are a couple of different ways to

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do it but Sir training up satellites is

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potentially most effective way to do it

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and then once you're captured the about

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a fifty percent chance that the tides

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um so what does that sudden peak in

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tidal heating mean for habitability so

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if there was life before would be

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completely sterilized from the capturing

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process probably but it's also i mean

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we're talking about like a couple of

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million years after the disc dissipation

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so that was that would be before life

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the earliest evidence they have real

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life on Earth this is sort of the same

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time scale is the moon-forming impact on

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earth which was a sterilization event so

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yeah you can think about the same sort

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of it's actually less dramatic than the

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moon firing because the movie forming

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impacts tripped into our surface this

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would just heat up the surface but only

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for about a million years did you

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mention that you had any candidates so

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that they've been looking so this is

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this is Kepler data for one that they

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thought was and it turns out this was

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actually a an unseen non transiting

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planet that was causing these timing

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00:16:06,150 --> 00:16:03,070
variations but this the search miss

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horny and kipping were doing was just

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00:16:11,569 --> 00:16:09,100
too I was looking for them and it's

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eventually going to look like that but

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you know they were going to be a lot

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00:16:17,040 --> 00:16:15,519
more and this one you can tell this is

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days on the bottom there so this is all

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very large variation the variations were

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00:16:25,800 --> 00:16:21,459
going to probably looking for for the

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dialects and moons are serve five to one

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00:16:31,319 --> 00:16:29,019
minute type variations so you need

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00:16:34,699 --> 00:16:31,329
really good data any lots of it to be

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very confident they're going to see it

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but potentially it could be there in the

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Kepler data if we mine it enough it's

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really computationally intensive to do

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though so is there some sort of minimum

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00:16:53,189 --> 00:16:51,310
ratio for satellite exchange like do you

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00:16:55,559 --> 00:16:53,199
have to have a mars-sized satellite

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initially for an earth-sized satellite

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00:16:59,400 --> 00:16:57,100
to take its place there's not a minimum

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00:17:02,790 --> 00:16:59,410
ratio but the you know the closer the

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00:17:06,060 --> 00:17:02,800
ratio the the higher the cross section

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00:17:11,520 --> 00:17:06,070
for it but yeah you know I further

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00:17:13,260 --> 00:17:11,530
for for that case the small guy there is

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00:17:17,700 --> 00:17:13,270
a hundredth of the mass of the other two

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guys so he's Oommen off there at you