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[Music]

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[Applause]

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thank you I'd like to acknowledge my

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colleagues that are contributors to the

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work that I will present and I've listed

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in here so if we want to understand what

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sort of atmospheres to expect around

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ocean exoplanets oceans

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what sort of biochemistry in their in

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their ocean for oceans that have enough

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water to have a high-pressure eyes

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they're separating the ocean from the

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rocky interior we need to introduce a

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lot of hydrophobic chemical species

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salts which would actually introduce a

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lot of crystal structures like clathrate

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hydrates filled eyes salty eyes that may

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actually fundamentally change our

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understanding of how material is being

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transported along high pressure high

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spangles so I wanted to make a point

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here that clathrate hydrates have very

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different characteristics than pure

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water and we've known this for quite a

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while what happens at even higher

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pressures beyond 1 GPA well some field

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Isis for example that form after

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clathrates will basically be doing

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dissociate but they dissociate and

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restructuring the field ice they could

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withstand pressures up to 100 GPA

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spanning the entire high-pressure Iseman

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so what are the sort of characteristics

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do they have so we looked at MD

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simulation we did an empty simulation

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for a filled ice of methane using the

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software CP 2k and we use that empty

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simulation to get the vibrational

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spectrum of the crystal structure of

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filled ice and I just wanted to make a

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point these are the results we got for

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the heat capacity so this would be the

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heat capacity for methane filled ice

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compared with heat capacities for pure

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water we see that it almost sits on the

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Dulong petit value which would suggest

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that filled ices have a very low Debye

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temperature and a sort of this weird

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behavior of clathrate seems to propagate

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also into the field ices in

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need a lot more work done in order to

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understand how they influenced the

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interior dynamics and and mass transport

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of ocean exoplanets when you have a

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high-pressure ice mantle so if these

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crystal structures that I mentioned

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actually exist in the interior a key

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question is what sort of solubility do

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they impose on the overlying ocean it's

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very important because it will tell us

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what sort of chemistry to expect in the

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ocean what sort of atmosphere would form

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around such planets and actually these

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solubilities are not very well known so

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we took advantage of data that is known

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from the chemical literature on

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hydration shell energies and we use the

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Kramer's theory for Brownian particles

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to relate the solubility of co2 in

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liquid to the solubility of co2 in class

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rates and yeah I forgot to mention that

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what I want to concentrate on a very

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specific problem sorry where you have an

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ocean where basically the seafloor of

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that ocean is clathrates rich in co2 so

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we built a theory that could actually

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tell us what the song ability of co2 in

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the liquid would be when in equilibrium

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with clathrates

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and when we compare this theory with

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experiments at low pressure up to a few

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hundred bars or model is the blue curve

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it goes through experimental data pretty

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well and we see a very distinct behavior

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where the solubility actually increases

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with temperature very different when

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class rates are not part of the problem

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what happens at higher pressure what

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happens is the actual seafloor that's

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that's a really big problem because we

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don't have direct information for the

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search for the solubility on the on the

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seafloor at a pressure of 1 GPA we can

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only infer that data from melting

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melting curve depressions so we took

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data from Ballinger in tallinn 2013 for

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system saturated in co2 and try to infer

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what sort of soluble

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you would have wedding equilibrium with

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clathrates and it's a very delicate

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problem if you assume an ideal sort of

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solution you get this green shaded area

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if you don't assume ID ality and you

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consider the fact that it's and you can

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correct for activity coefficients you

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get this red shaded area and the model I

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showed before with Kramer's theory is

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this black curve and it sits very nicely

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on the continuation of this inferred

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data so what we generally know from this

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modeling we only use this model to make

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interpolations it's very very important

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these models are not good to make

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extrapolations the experimental data is

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very very important but what we

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generally know when you are in equity

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room with class rates the solubility is

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not a strong function of pressure unlike

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when you use the Henry's law for example

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and it is reversed with temperature

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increases when the temperature increases

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this is what clathrates do when they're

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in the system so that's a very important

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thing to know the song the ability

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because if you want to consider the pH

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of an ocean you you basically want to

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solve this set of equations and you have

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five equations you need an you need a

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variable to constrain the system because

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you have six variables and for these

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particular planets if you have a sea

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floor that's composed of co2 it's an

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open system so if it becomes unsaturated

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with co2 co2 will enter the ocean

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because the clathrates will not be

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stable they will keep the ocean

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saturated so your solubility is

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basically what's governing the pH of the

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ocean now here they're charged neutral

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any equation that I've written seems

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extremely simple it's not true for Earth

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where you have a lot of interesting ions

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dissolved in the ocean and I want to

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touch on

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basically explain why we think it may

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have this simple form so recently there

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has been a lot of studies that have been

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published on what happens to Bryan's

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solutions at very high pressure

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and it seems that if the very

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high-pressure the end result is very

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different than than from low pressure

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where the salt is exalt out of the

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structure in very high pressure where I

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6 and I 7 are concerned ions dissolved

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in the liquid actually become

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incorporated as interstitials in the

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voids of high pressure isa

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juruá Tala studied the system Franco

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colander other studies and it's more so

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it's more correct for i7 than for I 6

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though but an interesting another

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interesting experimental result is that

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and talk about a paper public by Frank

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at al 2008 if you take such a high

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pressure I swear it has interstitials

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within its voids of ions of salt when

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you increase the pressure to 500 K it

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seems like that the ions are exalt out

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of the ice and form pure grains of dense

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salt why is that important and how is

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that what does that imply for ocean

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exoplanets that have a high pressure ice

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mantle so we solved for the thermal

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profile let's say this is the bottom

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this is the sea floor and then you have

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high pressure ice this is the thermal

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profile in the high pressure Einstein 6

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and I seven and this condition that I've

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written here is basically saying that if

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this condition is true which for these

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planets is true even if you have tiny

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fractions of rock in the planet then

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basically this is a scaling for the

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thermal conductivity and the temperature

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gradient of the melting of the melting

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curve that the bottom of the ocean the

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sea floor is actually constrained to the

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melting temperature the the melting

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curve of high pressure ice but being

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constrained to the melting curve of high

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pressure ice places are constrained on

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your ability to conductive ly cool and

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what this means is that high pressure

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ice that is upwelling would at some

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point tend to melt and basically

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discharge it's hot water into the ocean

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but if you're not basically melting your

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entire ice mantle and you're in a steady

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state then at a lower temperature you

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have to rican dents so there so I want

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you to have this picture in mind where

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you have an ocean that's discharging

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that you have high-pressure ice melting

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discharging water into the ocean and

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then rican dents and creating a new

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seafloor also another point that i want

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to show that contrary to icy moons

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because it's very high pressure

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adiabatic temperature profiles differ

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from the melting temperatures this is

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the melting temperature for I seven

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differ they started diverging to

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hundreds of hundreds of kelvins so if

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you want to create for example a brine

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pocket and you want to create localized

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mounting you need to overcome a

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substantial temperature barrier here so

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if you look at is Oh melting

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temperatures as a function of pressure

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the activity of the solvent which is

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water here that you need in order to

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create such a huge melting de pressure

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melting temperature a depression is you

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need the solvent to have an activity of

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0.2 we know from experiments that water

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does not reach these values somewhere

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around 0.7 so you cannot create brunt of

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pockets of brine so I I totally for a

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lot of things and I want to wrap it up

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in a in this sort of cartoon on an

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illustration that explains basically

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what these experimental data and the

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thermal profile basically shows us it

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shows us that that if high pressure ice

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up welds it melts into the ocean forms a

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new ocean floor but the new ocean floor

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that forms it actually has a high

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fractionation factor of ions dissolved

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in the ocean with a new ocean floor more

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so far i7 than for I 6 now stroll

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results for to in terms of what it means

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for the salinity of the ocean but if

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this part remixes into the mantle then

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when reaching the 500k threshold which

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we find that you indeed reach in the

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interior these ions that are

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interstitials in the ice actually start

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to dissolve out of the high pressure

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high structure and form grains of salt

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that sediment

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onto the rocky Court so on the one hand

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you have relatively pure water coming

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out and you have salt coming in so

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there's a pump that may actually start

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to desalinate the ocean over time and we

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calculated the time scale for this

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desalination process it depends on the

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fractionation factor of ions between

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liquid water and high-pressure ice and

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the and the melting rate and if the sea

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floor is i7 the timescale is very very

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short

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it basically desalinate sea ocean very

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rapidly if if it's size six which i

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think is more reasonable if something

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like I six then the time scale becomes

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very large but even this large time

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scale would suggest that you don't end

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up with more than milli molar

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concentrations of salt in the ocean so

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these oceans could be very rich in

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volatiles very poor insults which would

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say that the way that we've written our

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speciation of the eight of the carbonate

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system properly and what this would

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suggest is this pH profile in such

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oceans so the pH may go from as high as

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3.5 at the surface all the way to around

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2 at the sea floor so it's a highly

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acidic environment and if we plot this

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pH temperature die BH temperature that

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we have studied on a poly extrema file

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plot found that we've taken from kapitza

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all we see that it's a pretty barren

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region so it could be that it's a rare

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environment on earth and that's the

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reason why there isn't a lot of life

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here it could be substantially a harsh

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environment for life but in addition we

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have it's a poly it basically is an

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environment that is has many stressors

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it's not just the agent temperature it

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has to combat low salinity as I've just

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explained and

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way that you may do that is by

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introducing an ice camp and a reason

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that that may help with some of the

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issues of the environment being highly

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diluted with salts is with the with is

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with the fact that you tactic freezing

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within the pores of ice may actually

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create niches where you may reach higher

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concentrations that may be more

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interesting for combating hydrolysis and

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creating polymerization and I leave you

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with these exclusions a few minutes for

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hey as Steve ants again JPL I guess I

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didn't understand the mechanism by which

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I six exports salt to the bottom it

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makes sense to me based on what you said

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that I seven would do that the

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difference would be inefficiency so

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basically the the major point would be

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what is the fractionation because this

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this actually doesn't depend on I 6 or

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i7 right in terms of energy balance

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you're gonna have to melt and you're

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gonna have to reform a newly a new ice

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ocean floor that will mix the point is

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how much I salt you actually end up

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within this region so the difference is

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what is the fractionation factor of

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souls between the ocean and the

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high-pressure ice that would change

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between I six and seven for I seven it

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would be very efficient because it has

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larger voids for I six it would be

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somewhat less it's less efficient but so

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that so that's why yeah if I if I apply

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to this diagram with uh at Audi it's an

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exponential function kind of where i-70

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would end up with nothing

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okay so I six just has a lower carrying

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capacity yeah exact scale exactly and

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the key thing about the ocean worlds or

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sorry water planet sources ocean moons

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is that it pressures and in the water

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worlds are high enough that you reach

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this dissolution point at the bottom of

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the ice yeah I mean there's several I

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mean first of all on this arm so the

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question so for this pump to work you

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have to bring in relatively pure water

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and exit and and and you know and and

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and and basically sediment the ice right

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if you bring the salt back up then you

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don't have a pump so for ocean world's

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first of all you have a relatively at

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you saw the adiabat in the Mel

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they really diverge so for icing moons

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that temperature is actually because of

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the low pressure is not that that

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substantial it's a few tens of K you can

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easily overcome that and create brined

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pockets that can certainly migrate up

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certainly if you have like some models

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for typing a mixed ice rock layer it

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won't be a problem to basically opt well

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a brine pocket in this sort of situation

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it's very hard to do that you can't

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overcome a temperature difference of

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hundreds of K due to the high pressure

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and and again because beyond 500 K you

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don't get the ions as interstitials in

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the high pressure ice then you can't get

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the ions back as interstitials and you

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can't get brine pockets up there as well

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so the melting would probably happen

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somewhere here where the temperature

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difference between the adiabatic and the

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melting is not that hot so that's why I

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work here but it's not there work for

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icy moons is consistent with some recent

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literature on the two-phase convection

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and icy world and the moon okay it's not

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a contradictory okay thanks

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I'd like to encourage those with extra

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questions to talk to the speaker after

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the session so let's thank all the

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speakers