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you

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[Music]

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hello good afternoon as she said I'm

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Gila MonaVie and I'm filling in for Abed

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Mendez and presenting the results from

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the planetary habitability labs second

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earth-like worlds workshop where we

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studied habitability metrics for

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astrobiology if you like you can follow

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okay so what is a bit of habitability

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and how is it measured if we look at the

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map you can see that we have global

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terrestrial availability for primary

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producers as indicated by the net

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primary productivity and if you look at

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the equator you can see that the most

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productive areas or the most habitable

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areas are where we have forests okay so

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what is habitability habitability is the

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suitability of an environment for life

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it's formerly known as habitat

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suitability in biology specifically in

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ecology and habitability is usually

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quantified with indices that very very

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value from zero not habitable to one

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which is have oh these indices are an

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indication of the presence or abundance

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of some of the requirements of life a

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common misconception is that these

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indices need to consider all

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environmental factors to evaluate the

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habitability habitability is always

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evaluated by parts to understand

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individual contribution of one or more

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environmental factors and a library of

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indices is usually constructed to

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so we're presenting a general

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mass-energy habitability model current

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have ability models for example the

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habitat suitability model gives us a

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hability index that's proportional to

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the carrying capacity of an environment

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and so we get a numerical index that

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measures the capacity of the habitat to

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support a particular species or

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community our general mass-energy

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habitability model gives us a hability

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index that's proportional to the mass

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times energy that's available in a given

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environment so we get a numerical index

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that measures the mass energy capacity

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of a habitat to support life and how we

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get that index well we have to define a

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volume of interest and an amount of time

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we're going to watch that volume we

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measure the amount of energy going in

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and we measure the amount of gases of

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liquids and solids in that environment

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and that volume of interest and then we

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go ahead and make the calculation for

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the mass energy habitability index and

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here we have an example here we can see

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mass multiplied by energy and compared

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to a reference and this is how we get

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the mass part you can see it's a

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geometric mean of all of these masses by

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the way these masses do not include we

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don't include a biomass it's just the

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environment so we're using volumes and

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densities and the geometric mean and

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we're getting a normalized mass because

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we're comparing it to these reference

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values and this parts the energy and we

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can see that we're for this particular

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case we're using the temperature so

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we're talking about thermal energy and

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let's use that and so we have the mass

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energy availability index for some

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terrestrial environments now we're

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so again okay so we're considering for

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basic habitability elements we're

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considering the amount of gas

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represented by air the amount of liquid

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represented by water Livanos solid

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represented by earth and the amount of

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energy represented by fire so this is a

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little bit poetic but it's also somewhat

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accurate okay so our reference is the

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rainforest of El Yunque in Puerto Rico

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and since it's our reference it gets a

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mass energy habitability of exactly one

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now we're going to compare other biomes

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to that particular one and if we look at

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the ocean surface tropical we get a

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habitability value of 0.286 why so low

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well while in the rainforests we have

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lots of air lots of water lots of solids

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and lots of energy the ocean surface has

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lots of air lots of water lots of energy

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but not so much in solids and that solid

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you have there it's not that there is

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there aren't any solids in there you

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know but it's that it's a limiting

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factor there's little of that and so it

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drives the value down if we now go to

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the ocean depths you can see that the

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value is even lower well here what we

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have we have lots of water lots of

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solids but very little gases and very

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little energy so you get a lower value

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and if you go all the way to the clouds

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you get almost zero why lots of air lots

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of energy but compared to the small

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amounts of water and solids so those

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limiting factors are very important in

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bringing the values down but if you look

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at this more or less it seems reasonable

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you know more or less one woman what one

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would expect from these for this index

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and for what you would have for

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habitability comparing them but now

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let's see if this is actually valid so

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here we have a validation using

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terrestrial biomes what we did here is

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we compared the mass-energy hability it

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was calculated for each of those biomes

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again it was compared with the

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productivity the npp for 12 terrestrial

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biomes and you can see the data points

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okay and they make a nice little line

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there so this relation can now be used

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to predict the expected magnitude of

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biosignatures for example a higher

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global and PP means for more

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photosynthesis and thus more atmospheric

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oxygen produced okay so now we validated

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this let's try and apply it to planets

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now this is a model for an upper limit

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for planetary surface availability

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habitability and we assume that this is

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going to be for planets with a similar

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land ocean and atmosphere composition to

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earth and here we have the energy part

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that's this and a part of this where

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we're using the stellar flux and the

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surface of the planet and then for the

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amounts of solids and liquids and so on

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we're considering a thin surface layer

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okay and we need well the ocean the

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ocean fraction and we're assuming if we

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don't know how that planet is or where

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it is in time how it was at a certain

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point we're going to consider in this

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case that the atmospheres are the same

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so that will cancel in this in this

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equation and we just we only need the

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ocean fraction and to get the amount of

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ocean and the amount of land okay so

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this would be our mass energy

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availability index for planets our

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comparison is with earth okay so let's

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apply that applying that to early Mars

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with an ocean so earth is our point of

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reference so that earth then has a mass

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energy availability of one with a global

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NPP of 105 Giga tons of carbon per year

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now comparing that to early Mars with an

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ocean the mass-energy habitability of

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early Mars would be point zero two

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and that would correspond to a global

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MPG of 2.4 gig attends of carbon per

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year so there early Mars with an ocean

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was at least 40 times less habitable

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than Earth today okay so in conclusion

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habitability metrics allow us to

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identify and prioritize targets of

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interests simplify our understanding of

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habitable environments and compare

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results from simulations for examples

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when people are creating climate models

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for exoplanets you could use that for

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that the mass-energy have a living

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metric was constructed to characterize

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the potential habitability of

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environments based on the maximum

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quantity of mass and energy available

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for life a different metric could also

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be constructed to evaluate the quality

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of the environment our mass energy

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hability was validated using terrestrial

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biomes

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and we see that the general trend is

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that the suitability of planets to

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sustain a larger biosphere increases

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with the fourth power of the radius

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given that all other conditions are

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similar to earth therefore biosphere on

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planets slightly larger than the earth

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for example super Earths might be more

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susceptible to atmospheric chemical

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disequilibrium in other words bio

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signatures and that will conclude the

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all right if you're able to get to the

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microphone to ask your question please

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do so otherwise this creature and then

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we'll try to spot you thank you for that

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talk so your model is based on that it

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has exactly the same atmosphere land

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ocean and so on as the earth in

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proportion where no no it doesn't have

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to have the same proportions it's just

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similar so that you have land you have a

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rocky planet it has some amount of water

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and it has some atmosphere but we would

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expect we would want the composition to

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be somewhat similar so what would the

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index be for Venus hmmm what we haven't

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made that calculation but given that it

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has very little water start with at that

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point but well that would you know

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basically give it a very very low value

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oh well that's with our knowledge that

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it has a high water but in the context

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of an exoplanet just using the rate okay

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in a context of an exoplanet we would

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basically need to model that exoplanet

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and the conditions for that exoplanet we

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wouldn't be able to evaluate and until

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we get more information and then we

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could apply that but basically in terms

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of emotional animations of Venus means

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measuring the surface temperature really

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um yes yes measuring the surface

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temperature mm-hmm

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if you can get like we at this point we

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can already start to identifying

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materials in the atmospheres of

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exoplanets and probably a little bit

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later on a few years later on we'll be

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able to measure other aspects of the

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exoplanet so that's when we would be

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able to get actual values that are you

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know more indicative of an actual

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exoplanet but in the meantime we could

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still model exoplanets and we this is

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still useful for that purpose to be able

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to compare exoplanets based on the

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models okay

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awesome hi this is Rene Heller my

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question is the biomass production rate

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if I remember correctly goes with as you

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say their radius of the pen to the

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fourth to the force okay first question

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would be where does the number four come

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from its second how I mean there is no

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cap obviously soy to PETA would have the

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largest biomass okay so two things first

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of all we're looking for we're working

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at this point we're working with

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earth-like planets so Jupiter is not

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Earth alike and okay so we what we would

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do is yeah we would compare earth

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super-earths smaller smaller planets

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that are similar but there's a limit to

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where the super Earths lie but I don't

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quite remember where it was

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there's a certain particular value where

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you start getting gas giants oh yeah the

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number four okay so you look at this

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over here

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part of this comes from the surface of

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the planet and part of this comes from

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the volume and this is because this this

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happens where we you know we have the

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stellar flux times the times of the area

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for the energy and then you would have

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another are from from the volume

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consideration so it's a little bit of

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volume and a little bit of surface and

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that's where you get the art of the

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fourth power here okay we can take one

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more question if it's a quick one so the

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claim would be the habitability space

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value is high the planet is more likely

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to be habitable this value is low that

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is the ultimate aim could you repeat

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that again so a high value of the index

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should mean more likely to be habitable

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it's a quantitative yeah yes yes but

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surely with a number of priorities

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you're missing out to magnetic fields

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presence of water rock type actually

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there is no quantitative scaling between

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the value of that in

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see and the chance that planet really

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been habitable in reality okay at this

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point what we're doing is we're we're

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basically putting an upper limit to the

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habitability and later on we can develop

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this model or other indices so that we

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can take those things into consideration

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how those factors would affect how much

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of the solid liquid and gas is really

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available for for for life so I think I

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would argue that such metrics are quite

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good for sample selection to try and

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look at the planets for more information

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but I think to say it is quantitatively

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response proportional to habitability is

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just wrong sorry we're just going to

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have to cut the questions there let's go