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[Music]

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[Applause]

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hi I am Christine and I'm gonna be

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talking about hydrothermal fluids on

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Europa so you've heard a couple talks

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about hydrothermal systems already and

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this is an ocean world session so I'm

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sure I'm not blowing anybody's mind when

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I suggest that there might be

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hydrothermal systems on ocean worlds and

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in particular you might have heard about

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this from the Cassini mission when it

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flew through the plumes of Enceladus and

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actually detected for the first time

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observational evidence that hydrothermal

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processes could be occurring on ocean

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worlds and this in particular was an

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interesting result so they found oh

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that's

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just kidding mixing up my buttons so

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they found molecular hydrogen which we

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think in the high abundances that it was

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detected on Enceladus must be a result

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of hydrothermal chemistry and they not

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only found it but they found it in

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disequilibrium concentrations with

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methane and carbon dioxide such that you

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get a high chemical affinity or abundant

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and abundance of free energy for this

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reaction with anna genesis which is

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exciting it's a big astrobiological

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buzzword because methanogens they use

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this reaction to fuel themselves as a

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metabolism on earth so how does this

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work exactly right so we have

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hydrothermal systems somehow they're

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they're providing stuff that's fueling

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energy for life how exactly does this

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happen well you have some rock it has

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this stuff in it you pour some water on

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it you heat it up and it starts

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outgassing interesting things like

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hydrogen methane carbon dioxide those

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methanogenesis ingredients as well as

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other things and that's all well and

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good

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everything in this hydrothermal system

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is in equilibrium but then once you mix

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it with the cold ocean water that has a

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totally different chemical composition

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they clash and you get disequilibrium

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and in particular we think in the oceans

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of these icy moons you can actually be

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getting molecular oxygen so you can make

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oxygen in the icy surface radiation

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breaks apart water molecules there and

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if your surface is geologically active

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which we think they are an ocean world's

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then you can actually take this oxygen

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and deliver it

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into the ocean and then you have all

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these reduced species coming up from

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your hydrothermal fluids you have oxygen

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floating around in the ocean and

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disequilibrium

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for redox reactions so life takes

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advantage of the space equilibrium it

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extracts energy from that to push the

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system back toward equilibrium and uses

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that energy to sustain itself as a

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metabolism so could these things be

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happening on Europa we've seen evidence

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for it on Enceladus already the issue

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with Europa is that it's larger we think

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it's more complicated and we know

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nothing about it so how do we deal with

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something like that we consider all of

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the possible scenarios that it could be

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falling under so we know a lot about

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hydrothermal systems on earth we think

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we know something about how they might

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be working on Enceladus maybe on Io 2

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which is not hydrothermal but at least

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it's volcanic ly active and in the

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Jupiter system so we can apply all of

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these different geochemical constraints

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from all of these other bodies and say

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most likely your rope is falling

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somewhere within this parameter space of

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all these other analogs and look at

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exactly how these different parameters

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combine to affect hydrothermal

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geochemistry potentially an energy

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availability on Europa so we can start

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by making these lovely activity diagrams

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so let's pretend like we have a black

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smoker on Europa 300 degrees the open

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sea floor pressure 1,500 bar and we

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don't know what the pH of this black

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smoke or fluid is we don't know what the

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oxidation state is so we're just gonna

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let those vary and we're gonna look at

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generally for carbon at least what does

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the parameter space in that hydrothermal

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fluid look like so we see we can get all

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of these different things that depends

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on these parameters and now we can try

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to set some reference points to try and

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see if we're near this reference point

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what does our fluid look like so for pH

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we can calculate what neutral pH is as a

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function of temperature plot that on

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here and maybe say your rope is probably

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I don't know within two log units on

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either side ish of neutral pH so how

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would the speciation of carbon change as

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you move from higher pH to lower pH

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around that pH neutral point

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and same thing with oxidation state so

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the fmq buffer what is happening hey

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this is very dramatic the PHA late and I

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should take quartz buffer approximates

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redox conditions in ultramafic Rock on

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earth so we think there's alter mafic

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rock and some of these hydrothermal

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systems on earth it's not necessarily oh

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my gosh being buffered by these minerals

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but it's like around what you would

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predict the okay it's fine um so how do

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what you would predict the hydrogen

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activity to be if it were being buffered

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by these minerals so let's plot that on

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there again it's temperature dependent

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300 degrees this is where it falls and

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let's say maybe Europa is at the F and Q

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buffer maybe it's more reduced compared

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to that maybe it's more oxidized

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compared to that how would that affect

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the distribution the speciation of

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carbon there and then let's start

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playing around with the parameter space

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so we've seen that at 300 degrees this

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is what it looks like if we then change

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the temperature so let's make our

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hydrothermal fluid colder you can see

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that these more oxidized species get

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pushed out to zero degrees when you only

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have methane and vice versa when you

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make it hotter you're pushing ch4 out

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and getting more oxidized species so

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that tells us if you have higher hotter

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hydrothermal fluids then maybe oops then

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maybe you have more oxidized species

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unless you're really really reduced if

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you have cooler hydrothermal fluids

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maybe you have more reduced species

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unless you're very very oxidized so now

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I'm going to flip the parameter space

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around on you a little bit and instead

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of fixing temperature and letting pH and

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oxidation state vary I'm gonna do the

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opposite so I've fixed the oxidation

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state at this fmq buffer reference point

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here I fixed the pH pH neutral and now

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we're gonna vary pH one at a time and

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see what happens and you can see that as

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you move to more alkaline pH values all

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these charge species like my carbonates

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and carbonates start showing up

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especially at higher temperatures so

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essentially

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ph's job sorry is to control the

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abundance of charged species in your

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fluid that's its primary role so this is

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a lot of lines but just bear with me

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here so this is what I showed you before

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right we decided as we move down here as

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we move through more alkaline pH values

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you get more charged species and now

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we're going to vary oxidation state one

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at a time and see what its general

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effect is so we're at fmq and move to

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more oxidized values you can see that

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methane of course is getting pushed out

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there and it looks like at this oxidized

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reference point the role of pH is really

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dramatic right these plots look

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drastically different from pH neutral to

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pH neutral +4 whereas if you're more

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reduced they look exactly the same

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so pH and temperature have less of an

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effect when you're at more reduced fluid

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values when you're more oxidized the

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effect of pH and temperature is much

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more dramatic so that's interesting

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right we have some idea of maybe how

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these different parameters could be

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affecting the hydrothermal fluid

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composition on Europa but let's tie this

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into astrobiology because this is an

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astrobiology conference so how do we do

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that well with Ana Genesis buzzword

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again we looked at it on Enceladus let's

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look at how it might be working on

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Europa so I showed you on Enceladus they

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calculated the free energy the chemical

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affinity for the system found a Genesis

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reaction the way to do that is by

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calculating this reaction quotient Q and

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for that you need the ratio of methane

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to carbon dioxide you also need the

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activity of hydrogen so just to explain

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this a little bit more this guy I've put

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in orange because this we're assuming is

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controlled entirely by those parameters

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that I was varying in the hydrothermal

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vent fluid so we're not assuming re

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speciation in the ocean yet we're

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assuming this ratio is set by our

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hydrothermal vent hydrogen on the other

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hand who are assuming is set by the

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parameters of the global ocean so again

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you have this hydrothermal ch4 - co2

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it's mixing with hydrogen in your ocean

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they're totally different chemical

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properties they clash they create

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disequilibrium that give you energy from

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without

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so the issue here is that we have no

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idea what the activity of hydrogen is in

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Europa's ocean but we can at least try

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and maybe get some upper limits and

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lower limits so I'm going to assume that

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the ocean is probably not more reduced

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than the hydrothermal vent fluid so the

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most reduced it can be is at this fmq

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plus two buffer that I showed you before

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on the other hand the more oxidized it

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can be is much much lower than that

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right so I mentioned that you can get

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radio lytic oxidants from your service

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being delivered to your ocean this paper

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down here has actually constrained how

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many of those oxygens might be in

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Europa's ocean so we can assume as a

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lower-end member that oxygen and

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hydrogen are in equilibrium in this zero

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Degree ocean and because you have a lot

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of radio lytic oxidants you have very

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very little hydrogen and we'll assume

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that our hydrogen activity on Europa is

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somewhere between those two end members

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as you can see this varies drastically

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obviously you have free energy below

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zero that's not good for life but

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specifically you want to be above this

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reference point so biologists on earth

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have constrained the amount of energy

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you need from a metabolic reaction to

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actually sustain life it's about 10 to

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20 kilojoules per mole it's right here

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so you as you can see here if you want

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to meet this requirement you need to be

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up in this space up here so your ocean

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fluid needs to be pretty reduced maybe

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slightly more oxidized than the vent

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fluid but still it needs to be in this

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region over here yeah so reduced ocean

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good form without a Genesis oxidized

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ocean fabric without a Genesis does that

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mean if we have an oxidized ocean

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at fmq and ph-neutral that that's the

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end that methanogens

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in the sound of genesis the affinity

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can't change if we again start bearing

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these parameters No

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so let's look at what happens pH

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obviously we would expect not to have an

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effect right because we said that

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controls the abundance of charged

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species it has nothing to do with the

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siege for co2 ratio at least not if

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we're not considering reefs pca ssin

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whereas oxidation state we said does

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effect methane and co2 if you're more

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reduced to get more methane if you're

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more oxidized you get more oxidized

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species and you can see this right so

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this line shifts up and down ever so

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slightly as you change oxidation state

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but the takeaway is the same you still

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need to be in this more reduced region

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in order to be above that yellow line so

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does that mean that if we have a more

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oxidized ocean it's dead there's no life

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no because we can also consider aerobic

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reactions so let's say we have life

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that's using those radiologic oxidants

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to oxidize methane well we have

300
00:11:05,130 --> 00:11:03,730
constraints again on the amount of

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oxygen that might be in Europa's ocean

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from this paper here

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this is assuming hydrothermal processes

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or eating some of that oxygen this is

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assuming the oxygen is just building up

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and not really being reduced but even so

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even at these low levels of oxygen

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predicted in this paper you still have

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tons and tons of energy for aerobic

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methane oxidation and in fact it's well

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above again this 10 to 20 kilo Joule per

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mole level that you need to be at in

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order to sustain life so this looks

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00:11:36,030 --> 00:11:33,760
really good but again I fix the

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oxidation state I fixed the pH we have

316
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no guarantee that your rope is

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00:11:40,350 --> 00:11:38,710
hydrothermal fluid actually looks like

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that so what happens if we vary that

319
00:11:50,889 --> 00:11:48,160
well again we've decided oxidation state

320
00:11:53,100 --> 00:11:50,899
changes your ch4 to CO 2 ratio so we

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were here before as we move to more

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oxidized conditions the energy shifts

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down as we more to move to more reduced

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conditions the energy shifts up but even

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so again you're still like well above

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400 300 kilojoules per mole well above

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that 10 to 20 kilojoules per mole level

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that you need to be at in order to

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support life so good news for methane

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oxidation so summary here right

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but that agenda said oh my gosh with

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Nana Genesis you need to be above the

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00:12:25,780 --> 00:12:23,690
yellow line if you're have a very

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00:12:27,160 --> 00:12:25,790
reduced ocean fluid that's good news you

335
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meet that if you have more oxidized

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fluid that's bad and it doesn't look

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00:12:32,889 --> 00:12:31,070
good from it down to Genesis but that's

338
00:12:35,199 --> 00:12:32,899
fine because even if you are at more

339
00:12:37,449 --> 00:12:35,209
oxidized conditions like here you can

340
00:12:41,230 --> 00:12:37,459
still use aerobic oxidation like

341
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methylene oxidation to support life so

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in general our hydrothermal parameters

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even though they changed drastically the

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composition of your hydrothermal fluid

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and they do change the amount of energy

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the amount of life you can support

347
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absolutely you still can support some

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life from aerobic reactions from methane

349
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oxidation regardless and I just wanted

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to add that this is also great for

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Europa clipper which is going to go up

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hopefully sometime in the 2020s and

353
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measure the composition of the ocean

354
00:13:08,139 --> 00:13:06,769
from the plume so we can take those

355
00:13:10,960 --> 00:13:08,149
measurements and trace them back to

356
00:13:12,699 --> 00:13:10,970
these kind of models to figure out what

357
00:13:14,620 --> 00:13:12,709
kind of hydrothermal processes might or

358
00:13:15,880 --> 00:13:14,630
might not be happening on Europa and how

359
00:13:18,280 --> 00:13:15,890
much chemical energy might be in the

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ocean and with that I will take

361
00:13:26,679 --> 00:13:19,440
questions

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[Applause]

363
00:13:31,999 --> 00:13:29,579
okay so we have time for one or two

364
00:13:34,639 --> 00:13:32,009
questions and if anybody's cellphone we

365
00:13:37,489 --> 00:13:34,649
have some feedback going on so the front

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00:13:43,939 --> 00:13:37,499
row right here does anyone else feel

367
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like okay nevermind carry on okay so if

368
00:13:49,789 --> 00:13:46,079
there's a measure disequilibrium that

369
00:13:52,819 --> 00:13:49,799
might suggest that life didn't use it so

370
00:13:55,100 --> 00:13:52,829
is there a way to use this modelling to

371
00:13:57,679 --> 00:13:55,110
calculate the maximum amount of

372
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measurable disequilibrium that still

373
00:14:02,119 --> 00:14:00,540
allows for some life to it around yeah

374
00:14:03,489 --> 00:14:02,129
so this is a big question and this is

375
00:14:06,199 --> 00:14:03,499
something people raised with the

376
00:14:07,609 --> 00:14:06,209
methanogenesis chemical affinity also

377
00:14:10,999 --> 00:14:07,619
like if there's all this free energy on

378
00:14:12,439 --> 00:14:11,009
Enceladus why isn't life using it and we

379
00:14:13,879 --> 00:14:12,449
don't really have this constrained well

380
00:14:15,650 --> 00:14:13,889
enough because we don't know how much

381
00:14:18,229 --> 00:14:15,660
life could be on Enceladus and based on

382
00:14:20,329 --> 00:14:18,239
that we don't know how much of this how

383
00:14:22,100 --> 00:14:20,339
much it's going to drive the system

384
00:14:23,629 --> 00:14:22,110
toward equilibrium so maybe without life

385
00:14:25,069 --> 00:14:23,639
you would have even more chemical

386
00:14:27,409 --> 00:14:25,079
affinity than what we actually measured

387
00:14:29,269 --> 00:14:27,419
we don't know something I would like to

388
00:14:30,679 --> 00:14:29,279
do on earth actually is look at in

389
00:14:32,449 --> 00:14:30,689
systems where we know there are

390
00:14:34,579 --> 00:14:32,459
methanogens how much free energy is

391
00:14:36,769 --> 00:14:34,589
there for methanogenesis is it zero or

392
00:14:38,239 --> 00:14:36,779
is it still some positive amount because

393
00:14:39,379 --> 00:14:38,249
you still if it's zero that kind of

394
00:14:41,449 --> 00:14:39,389
tells you the system might be in

395
00:14:43,400 --> 00:14:41,459
equilibrium you can't really support

396
00:14:44,869 --> 00:14:43,410
more life but is that necessarily true

397
00:14:46,189 --> 00:14:44,879
it would be really interesting to

398
00:14:50,239 --> 00:14:46,199
compare how we know this works on earth

399
00:14:55,949 --> 00:14:53,009
all right we will keep moving along

400
00:14:57,430 --> 00:14:55,959
thank you very much one more round of