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[Music]

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today we're going to tell you about our

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proposal that we propose this weekend at

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our FG and it involves two models both

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related to water worlds

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the first model that we're going to talk

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about is a planet migration model that

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explains the formation of the water

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world and then Richard will talk about a

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more chemistry based planet model when

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we get to him so just a little

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definition of what we mean by water

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world we're talking about super sized

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planets so between 1 & 8 Earth masses

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that are composed of at least 30% water

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so these are deep surface oceans that

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we're seeing in these planets the

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observational signature of a planet like

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this would be a low-density and if we

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could get a spectrum in the atmosphere

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we would hopefully notice some water

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vapor in the spectrum and so this

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proposal was a response to the NASA

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probes exobiology call and specifically

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we're looking at exploring the range of

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planetary environments and amenable to

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life so you all saw this plot yesterday

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but basically what it's showing is some

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lines of constant composition on a mass

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radius diagram for known exoplanets

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known terrestrial exoplanets and what we

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notice here is that a lot of them are

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very low-density up here on this line of

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water density and we expected to see

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that because we see a lot of low density

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planets and moons in our outer solar

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system but what we didn't expect was

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that some of these are found really

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close to their stars and particularly GJ

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1214b is a planet that is in the

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habitable zone of its star and seems to

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have a very low density and is a really

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good possible option for a water world

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and so the other thing that is

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interesting is right now observational

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biases make it so that it's difficult to

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find habitable zone earth sized planets

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so this plot shows the detection

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completeness of our current X Planet

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surveys and you can see that this

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section

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here where earth is is pretty empty

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there's it's really hard to find those

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planets so in the near future we're

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gonna start finding a lot more

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super-sized planets in the habitable

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zone of their stars and hopefully some

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of them we will discover our water

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worlds and so that's kind of what we're

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going to look into and so the way that

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you create a water world there are a few

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different ways but the tricky part is

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that it's tough to get enough water to

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create this water world in the inner

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solar system so what we're proposing is

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a method described by Raymond at all in

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which you form the water world

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late and plug the planet formation stage

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in the outer solar system and then it

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migrates in in the wake of a migrating

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hot Jupiter and so this is an n-body

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simulation run by Raymond at all in

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which a hot Jupiter is migrating through

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a gas disc inward and planetesimals are

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getting caught in resonance behind the

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hot Jupiter to result in a habitable

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zone water rich planet so for our models

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we're going to be looking at the Alpha

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Centauri system and so we chose these

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stars because they all have very similar

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composition so the we can treat the disk

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composition gradient as a constant and

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they have a range of different stellar

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types for us to use for our models but

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for the actual models this is a triple

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system but we're going to treat this as

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three independent star systems and just

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use these stars as the initial

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conditions for our for our models so the

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the first star part of our proposal is

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to set up a suite of n-body simulations

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kind of like the Raymond at all paper

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but to explore a range of different

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initial conditions for the disk

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composition and well the disk

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composition will keep constant between

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all our simulations but will change the

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initial positions of all of the

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planetesimals and the the number of

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planetesimals in the disk and yeah so

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then we'll run that these simulations

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for about 100 to 500 million years

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and end up with hopefully some of them

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will form water worlds in the habitable

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zone of their star and we'll end up with

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orbital elements for each of these water

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worlds and some physical properties that

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can be fed into the next model which

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Richard will tell you about okay thank

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you very much so we're gonna go ahead

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and take the parameters from though the

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orbital parameters from the initial

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model as well as the physical dynamics

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of each water world and take those

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parameters and plug them into a GCM

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we'll talk about that here right off the

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bat but before we do that before I make

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extrapolation is to try and determine

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what are the parameters of habitability

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for an exoplanet over a spectrum of

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different types of stars it becomes

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imperative that I think that we actually

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constrain our models with real world

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data with the launch of Geneva's T and T

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and test that becomes even more

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imperative because if a person was to

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make extrapolations regarding an

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exoplanet without constraining their

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model with real world data that becomes

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nebulous and it runs a little bit on the

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side of hinky okay I think that's a

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scientific term so how do we do this

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then in our proposal we state that what

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we're gonna do is we're going to try to

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work with the model parameters to try

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and validate our models utilizing world

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data fortunately we have now several

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decades of data regarding terrestrial

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planets that exist within the habitable

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zone is everybody here already knows so

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we take the our solar system as the

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model we run our Hubble's own validation

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for the spectrum of the habit of zone

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Venus Earth and Mars and then bracket

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with an outlier which we'll talk about

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which will be tightened so I'm only

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gonna run briefly through this but what

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I want to impress is that in terms of

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the model validation we use royal data

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to explore habitability within our own

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solar system where we know that there's

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abundant life at least on earth there

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may have been potentially early life on

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Venus that's the idea and then Mars at

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least is marginal at best so to start

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here we have of course the

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spectrum of Earth Venus and Mars the

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abiotic systems tend to run towards a

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thermodynamic equilibrium and you see a

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clear co2 signal Mars house is a little

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bit of nebulous issues regarding methane

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the may or may not be biotic depending

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on what set of camp you fall into but it

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does bracket the outside portion of

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habitability when it comes to earth it's

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very important to go ahead and constrain

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the Earth's system and say okay what is

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the minimum on a day that we need to

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really look at our planet which is a

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known thriving biosphere that

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interconnects all the different systems

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on the planet and actually modify the

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planet can we see an unambiguous signal

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if we examine our own planet as an

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exoplanet

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fortunately great works been done on

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this by the Robinson a tall team in 2011

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during the Deep Impact survey of a comet

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they were really sharp and they turned

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the cameras back around and looked at

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our own planet

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and basically looked at our planet just

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like a technological society we look at

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our planet to determine if that's a

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habitable planet and how much data could

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we extract out of a hundred meter or

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excuse me a 100 pixel survey so if you

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look at our planet we can actually learn

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quite a bit just from a little bit of

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data and we can quantify our system in

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terms of surface features including

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ratios of land mass versus ocean

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approximately 50 percent cloud cover run

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that through time combine that with

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spectroscopic work and lo and behold bio

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signatures pop out in terms of looking

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at the atmospheric signature

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corresponding as well to habitability of

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ocean determination and habitability by

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composition some of the features you

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already know ad nauseum water

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a strong methane signal owes three are

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very strong features for habitability so

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what is the minimum amount of data we

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can then extract and utilize to

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determine if these planets are habitable

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we go up with with tests we go up with

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JWST that's very limited observation

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time we need to be able to maximize the

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data retrieved and be able to interpret

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so we don't Forge either a false

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negative or false positive

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this is a an image of the transit of

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Venus in front of the Sun let me back up

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a bit

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sorry turns out that you can actually

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get the profile of the atmosphere from

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this little tiny sliver here the

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atmospheric limb so four atmospheres

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that are transparent the flecks of

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photons is very low it's something on

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the order I think 100 and someone can

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correct me about 120 part per million

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photon hitting a CCD and that's over

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four parsec well four parsecs I believe

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so here's the Venus spectrum that

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wiggling in the laser pointer is coffee

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probably nerves and then you can see in

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fact that Venus has an atmospheric

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signature and now this trick note

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atmospheric city Atmospheric signature

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that is indicative of the hydrocarbons

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up in the atmosphere and we look at it

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closely you get a little bit more

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regarding circulation so this actually

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also shows a little of that mystery

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circulation that's analogous to Hadley

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on earth and water vapor at

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approximately 35 kilometers ok so then

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we've parameterised now if our models

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that we were able to build prior to

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bringing into exoplanet data we can

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parameterize and truth' them to our own

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solar system and that's vital it's a

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vital step I believe we can then also

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bracket it using a biotic system or

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prebiotic system to tighten the Titan

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system also shows methane and ethane at

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different latitudes and so again minimal

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data provides maximum output so how do

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we approach this to the exoplanet

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question the exoplanet question has a

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lot to do with models and obviously

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models have strong vulnerabilities in

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terms of their sensitivities and by

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necessity you can't put it in front of

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data into a model otherwise you end up

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warping the model and having gunk pop

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back out so we find out what are the

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most important processes and with the

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experience of students in this room and

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others in the community I feel confident

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that we can actually parameterize our

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solar system and utilize those

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parameters and then plug them into an

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exoplanet model in terms of a couple of

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geochemical model it's possible to

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modify something that we know has

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already successfully parameterised an

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ancient world that can be ground truth

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so to look for an ancient world we go

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back in the geological record we start

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to examine the snowball earth snowball

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earth is a period of time of geological

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history where the vast majority of the

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Earth's surface was covered in ice or

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snow and pack ice which led to mass

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extinctions it's also implicated in

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subsequent biodiversity explosion now

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one of the other processes that occurred

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during that time was a shift from a

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reductive ocean atmosphere state to a

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net oxygenated atmosphere so if we can

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do that for our ancient planet who's to

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say that we can't do that for an

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exoplanet now some of you may be

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wondering say well that's a lot to take

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on why would you do 3 stars well it

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turns out is Jonathan already mentioned

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this is a very attractive system in fact

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I think should be probably the highest

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priority system look at for habitability

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one of the reasons of course is

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metallicity and is that we've seen in

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the talked prior yesterday the medalists

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key constraints obviously the relative

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elemental abundance on the subsequent

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planets however another issue is that

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you have three stars starting from a

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initial homogenous state that evolved

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and diversify over time but if you look

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here the spectral types are very similar

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to earth you have a star that brackets

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our own Suns habitability ají system in

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a case system and then Proxima Centauri

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so what are the limits and vulnerability

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in a water world around those stars we

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can modify and we can go ahead and mix

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some analyses to determine what a water

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world would look like but I would argue

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that there's an interval of water worlds

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that we can evolve around stars that are

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not only habitable but super habitable

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for reasons that we can discuss maybe

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one on one is a function of time so what

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is this all about

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ultimately it's to try and determine

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what is a spectral characteristic of

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hypothetical planets driven by abiotic

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processes you can form both an

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oxygenating atmosphere as well as

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reducing ocean atmosphere system without

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invoking biotic process

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so when we see that signal for that one

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pixel data let's go ahead and interpret

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that as a starting starting point for

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subsequent studies and just really

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quickly because I think we're out of

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time this is our 3-year plan basically

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the the first model we described will be

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built in and run over the first two

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years and while the second model is

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simultaneously being built and

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calibrated and then in the third year

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will be applied to the Alpha Centauri

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system and so lastly I just want to

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thank everyone that was involved in the

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RF G this weekend it was a ton of fun

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and I'd specifically want to thank the

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organizers who really threw us off the

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deep end

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and gave us a chance to to really get

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into the proposal writing process and I

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didn't have any pictures so I took some

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yesterday thank you

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so we didn't get too much of a chance to

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talk about the actual model so the model

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actually incorporates atmosphere it's on

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a 42 level atmospheric coupled model to

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ocean atmosphere communication so I'm

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aware of what you're talking about

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there's some issues in terms of

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habitability of water worlds because

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it's a function of mass and it's a

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stepwise transition about one point six

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earth mass from a potentially habitable

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world to more of a Newtonian system

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where you retain some of those light

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hydrocarbons they also form a

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supercritical vapour liquid phase so

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habitability is also a question you can

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consider habitability may be a function

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of terrestrial habitats may not

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necessarily be the outlook to look for

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but I do agree with you and I think you

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made a comment yesterday about

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habitability should be expanded because

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it is also the issue of icy worlds and