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[Music]

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first I want to thank everyone for not

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only staying to the last day but also

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the talk right before lunch or all

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troupers so I'll try to keep it brief

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for your sake so first I'm going to go

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over you know some stuff that you've

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heard a lot in this section that próxima

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B has a very uncertain formation there's

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three main formation pathways that could

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have preceded Institute for mation where

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it formed effectively where we see today

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it could have formed farther out in the

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disk and migrated inward or it could

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have formed via some dynamic instability

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where it formed somewhere in the disk

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and some planet planets scattering

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catapulted the planet to where it is

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today and in those processes Proxima

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beat could be water rich or poor today

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it could have a lot of volatile the

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hydrogen envelope like Rodrigo talked

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about earlier but these are things that

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are rather poorly constrained and need a

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lot of modeling and additionally you

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know as we heard about earlier with no

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radius constraint we can't exactly pin

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down what mass it is exactly so there is

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still regions of parameter space albeit

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unlikely from what we saw earlier that

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it could have an extended hydrogen

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envelope and be a mini Neptune but

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there's a lot of modeling that needs to

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be done to constrain these things

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additionally as Rodrigo pointed out pre

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main-sequence water loss in this planet

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is going to be very important to

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understand how much water exists on it

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today if it's formed with a lot of water

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in the beginning so as you can see on

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the right-hand side here

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Proxima be if it existed at its current

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orbit for its entire lifetime existed

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within or sorry interior to the

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habitable zone it to be careful with

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that interior to the apples own for

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around 170 million years you know with

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some uncertainty and during that time as

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Rodrigo showed it could have undergone

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some substantial water loss with you

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know several Earth oceans maybe up to

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ten Earth oceans being lost depending on

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your model parameters further

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complicating this as we saw on an

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earlier talk by Rory Barnes that tides

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are definitely going to be important for

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any M dwarf planet residing in the

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habitable zone of their host stars and

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these tides can tend to circularize the

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orbits dance obliquity z-- drive tidal

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heating and it can place the orbit in a

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tidally locked state where it could be

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in some flavor of a spin orbit residence

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you know a 3 to 2 or 1/2

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potentially and this you know as we saw

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earlier in GCM modeling by Tony del

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Genio can be very important for

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understanding what the planet looks like

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today depending on its composition so

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these are all very extremely important

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for understanding Proxima beat today

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so with these for physics in mind you

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know we need to simulate these in a very

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cohesive framework to understand what

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Proxima beat can be today so for big

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ones we have tides the evolution of the

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star itself atmospheric escape is where

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ego talk talked about and the Earth's

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like interior physics that can drive you

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know the formation of a core and can

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actually couple with these different

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models especially the tidal balls so we

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do is we actually couple these for all

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these physics in a framework v planet

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that's presented in barns at all 2017

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which is still under review we use the

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title evolution the compensated leg

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model of frost melo at all 2008 the

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stellar evolution we use young style

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tracks that are appropriate for low mass

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stars like Proxima use a third one D

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thermal interior code developed by Peter

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Driscoll and collaborators and finally

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we use the atmospheric escape formalism

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of the air cave at all which is a

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representative Rodrigo's 2015 paper now

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I want to be careful I want to claim

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that we're not modeling everything in

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the system as my Klein pointed out

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there's a lot of higher-order physics

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that need to be resolved for a very

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robust estimation but if we're going to

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simulate all these different physics to

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understand how Proxima B is today and if

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I want to simulate all these on a PhD

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time scale we have to use these 1d

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models in this framework so we can still

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come up with some robust statistical

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conclusions now I want to say that I am

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committing a cardinal sin of this

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session I'm not working in a Bayesian

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framework but before you throw things at

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me I want to mention that when you

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combine all these physics this is a

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massive parameter space upwards of 30

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parameters so even though V planet is

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blazingly fast I don't care how much

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computer time you have you're not going

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to resolve every single dimension now

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this is stuff we're working on but here

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I present some bookend and member

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simulations just so we can see how these

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different flavors of evolution actually

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progress so we can have an idea of how

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these different physics actually couple

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in reality so first one thing I would

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have note about the tides here we

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work with the constant phase light phase

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like model and that has to do with this

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nebulous parameter Q and Q effectively

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just parameter eise's how efficient it

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tides are how fast the tides proceed so

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on the left here small title Q is

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consistent with an earth-like planet

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where you have these surface oceans

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driving very fast tidal evolutions this

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is efficient dissipation and a large

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tidal queue could be some planet with a

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very extended atmosphere like in Neptune

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let's say so these large tidal queues of

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order like 10 to the 4 let's say lead to

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inefficient dissipation so in our

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coupled title model we effectively take

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the harmonic mean of the tidal Q and if

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anyone was asking about why that's

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physically justified I'll be happy to

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get into that later but effectively what

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we do is we include a thermal interior

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portion a portion due to oceans and an

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envelope in this onion planet model

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represented schematically below and we

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simulate three major cases the first one

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is no ocean case where we just have the

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1d earth model Peter Driscoll driving

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the evolution of the planet and its

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growth of the mantle and the internal

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core of the planet actually gives it a

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title Q of a few hundreds webside now in

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our second case the ocean case we just

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slap on an ocean of the planet assuming

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a liquid surface ocean with the title Q

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consistent of Earth which is you know

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mostly tightly driven by its oceans and

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we compute the net tidal Q this way but

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when the planet is in the runaway

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greenhouse phase there's not going to be

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any liquid water present on the surface

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instead it's going to be in some steam

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atmosphere so we neglect that term from

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our calculations so in our final case

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the envelope case is our full onion of a

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planet where we have all these different

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terms and we use an envelope Q of 10 to

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the 4 consistent with that of Neptune

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drive-bys and Hamilton 2008 but again

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there's a caveat when the envelope is

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actually present that's going to be

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exerting a high pressure on the water so

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it's likely going to be super critical

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so we again neglect the ocean term while

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the envelope is present so now we're

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going to look at how some of these

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parameters evolve as function of time so

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here we have the title Q as a function

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of time for our cases and note that we

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also have this Cpl case which is just

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our base case effectively where we have

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a constant tidal queue of 12 through the

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whole simulation just as a good

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reference for it

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so you can see the envelope ocean and

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ocean case are all dominated by this

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interior evolution as they all progress

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to a title cue of a few hundreds and

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then you see this abrupt phase

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transition and this occurs when the

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planet actually leaves the runaway

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greenhouse phase there's some you know

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epic monsoon where all the oceans

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condense and this leads to very rapid

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tidal evolution as the tidal keep

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plummets and we can see how this

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actually impacts the orbits if we look

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at this orbital eccentricity on the left

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and the semi-major axis on the right so

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again for both of these cases you see

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that it's pretty much the mantle the

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thermal interior dominating this tight

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little evolution during the during the

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runaway greenhouse phase and again when

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you leave that phase that's when the

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tides really turn on you have this

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orbital circularization and your

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semi-major axis starts to decay due to

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efficient tidal dissipation now we can

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look at tidal heating to see what goes

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on here now you see a spike that I'll

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get to that

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so you see initially that the new ocean

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case the thermal interior again

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dominates earlier but you see this

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little bouncing of the envelope here

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what's going on here so what this

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actually is as the planet is losing

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hydrogen due to hydrodynamic escape the

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radius actually changes and we use a

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some ATO bat models from Eric Lopez I

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believe to actually calculate the radius

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as a function of hydrogen mass here so

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that's what's going on for this little

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wiggling now again as you guess it this

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spike is due to oceans condensing the

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efficient tides turn on and you get some

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substantial tidal heating actually in

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excess of IO which is of order two watts

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per meter squared now this planet isn't

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going to be throwing up its guts like IO

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is instead this title dissipation mostly

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happens at the ocean rock interface here

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so this could warm the ocean but

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probably not appreciably at this tidal

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heat flux but for closer in planets you

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know as the tidal forces get stronger

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depending on your orbital distance to

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the star you can get more substantial

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title heating in a scenario like this

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and that was explored in a 2013 paper by

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Rory but I won't get into that anymore

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and then finally let's look at how the

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hydrogen envelope on the Left that mass

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and the water content on the right

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actually vary as a function of time so

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in our two cases where we actually have

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liquid water we have the Oh

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in case in blue which doesn't have the

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iodine envelope and then and then the

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envelope case in the orange line which

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does have a hydrogen envelope hence its

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name we can see that the envelope

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actually decreases due to the

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hydrodynamic escape such that the entire

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envelope has been not pushed off the

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planet but it fully escaped by around 80

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mega years or so and in this time it's

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interesting if you look at the water

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curve you see that that hydrogen

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envelope has protected the surface water

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in this case and this can be in of

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course once you see the oceans condense

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and you lead the runaway greenhouse

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phase there's no water in the atmosphere

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that could be subject to fatalis and

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subsequent escape but if you look in

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this case you can see that the hydrogen

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envelope can actually be very efficient

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in preserving some surface water so you

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see it doesn't lose anything the

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envelope is present and in this you know

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obviously fine-tuned case we end up with

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roughly one earth ocean of water which

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is excellent now again like Rodrigo I'm

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not going to claim to a solve Proxima

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Centauri B but these are some

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interesting cases that must be

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considered for a planet like this

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especially when there are large

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uncertainties on its formation so I'll

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conclude and say that coupling these

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physics like although they are 1d models

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and they are rather simple but they're

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very important to understand the

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cohesive evolution of sussel such a

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system especially when there are non

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zero cases that can lead to a habitable

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Proxima B today you know as an optimist

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is what I hope for albeit likely you

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know it's unlikely and we have this code

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bee planet that allows us to couple

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these and simulate a large number of

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these not necessarily you know 10 to the

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40 or so but still enough that we can do

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some sort of these Bayesian Alice's that

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Rodrigo presented earlier and of course

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this depends a lot a lot on its

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formation which needs to be constrained

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by models in terms of how much water it

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has and its hydrogen envelope and of

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course this is a huge parameter space to

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explore so if we are going to do any

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sort of Bayesian stuff with this coupled

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model we have to speed it up and I will

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you know plug myself of course that this

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is some work I'm doing with using

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machine learning to actually speed this

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up and appropriately sample high

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dimensional parameter spaces and with

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that I'll be happy to take any questions

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thank you very much David so yeah we do

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have time for questions for those of you

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who are not too hungry I could go ahead

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and get your coffee earlier as well I

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have a question sort of for all the

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speakers in this they talked about this

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beep planet model is this model

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eventually going to be available somehow

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to the community of interested Koreans

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from these type of models I guess that's

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my more of a question for me yeah so I

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yeah that is that is definitely the goal

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and we are working towards that so uh

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you know I can't give you a precise time

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frame but hopefully within the next year

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or so we'll be a being able to really

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set to the public so we're working

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towards our plan and this is a

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potentially naive question this is not

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my field of expertise can you use the

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known or upper limits on the

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eccentricity for proxy Envy to back out

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and say whether there's a notion or not

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you've got if there's a notion it should

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have a title dissipation and you should

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have a circular orbit if it's very good

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at anticipating an orbital energy but if

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there if it's an eccentric orbit you can

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argue that there can't be much ocean um

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so I think in this case whether or not

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there is an ocean or not is

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predominantly dominated by the

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uncertainties on our atmospheric escape

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model I guess where we go spoke about

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earlier referencing him a lot that

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there's just a substantial uncertainty

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with the planets previous XUV luminosity

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evolution which we do try to model in

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terms of its eccentricities higher

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eccentricity you get more orbit average

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flux right that is not a case we probed

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here but even with if we just evolve it

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with an exome tricity of 0.35 and keep

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that constant it's still that luminosity

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evolution that's driving this although

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when you get into a framework like this

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that's when we can start to split hairs

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and see like okay how much oceans you

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actually need to begin with if you start

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in a high luminosity state and with our

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Cpl model it's not strictly valid at

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higher eccentricities like that we need

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to switch to a CTL model for example

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they can handle these higher

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eccentricities but here we focus more on

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the low eccentricity regime thank you

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all right any more questions all right

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well then I thank you all for coming to

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this session when I could break for

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lunch before we go I want you know I

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remind you all to to please fill out the

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survey formula that you can get at the

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kiosk across from the registration desk

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but let's say I go ahead and thank all