Alternative biochemistries and supercritical fluids

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sociotard
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Alternative biochemistries and supercritical fluids

Postby sociotard » Wed Apr 13, 2011 10:39 pm UTC

xenobiology question here. I was reading about possible alternative solvents to water in alien biochemistry, like methane, ammonia, or even stranger things. Is there a reason that supercritical fluids would not work? I ask only because Venus and all the gas giants have large oceans of supercritical fluids of one kind or another. If there was a bug that could live in that stuff . . .

My guess is that a planetary ocean of supercritical fluid would vary too much in density to be very life-friendly. Life seems to like a nice constant niche to evolve into.

What do you think?

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Meteorswarm
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Re: Alternative biochemistries and supercritical fluids

Postby Meteorswarm » Thu Apr 14, 2011 4:32 am UTC

The main supercritical fluid I can think of is CO2, but it doesn't have the polarity that water has - and that polarity is what makes it a good solvent for life because it can dissolve lots of interesting things. Could be possible, though.
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Re: Alternative biochemistries and supercritical fluids

Postby Cobramaster » Thu Apr 14, 2011 6:54 am UTC

While possible life would be "interesting" for organisms in a CO2 supercritical environment and they would have a narrow range of conditions in which they could survive. The main issue would be the conditions existing long enough for life to begin if the timescale is anywhere close to what it seems on our planet.
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sociotard
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Re: Alternative biochemistries and supercritical fluids

Postby sociotard » Thu Apr 14, 2011 2:59 pm UTC

Yes, Venus has a sea of CO2/N2 supercritical fluid

Jupiter (probably) has one of H2

Saturn H2/He

The other planets, including the gas giants, don't have any, except maybe in pockets. Frex, earth has supercritical H2O around underwater volcanos.

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Re: Alternative biochemistries and supercritical fluids

Postby Cobramaster » Thu Apr 14, 2011 3:40 pm UTC

Actually Venus is well outside of the Supercritical range for CO2, and while Jupiter and Saturn may and probably do have super critical oceans of hydrogen and helium thats basically all they have with some methane and ethane. But then you get to the fact that they are so cold reactions involving those species don't happen spontaneously and for a metabolic process there is not much to metabolize.
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Re: Alternative biochemistries and supercritical fluids

Postby Soralin » Thu Apr 14, 2011 4:19 pm UTC

Well they're not necessarily that cold, at least not once you get down into the atmosphere a bit:

Jupiter:
Image

There's a nice region there, just below the methane and water clouds, that has a nice Earth-like temperature (although it wouldn't be supercritical there) Distances are km above and below the pressure level of 1 bar. Although it might be a bit cloudy, photosynthesis might be a bit difficult, not sure how light levels would be at that depth, and it is quite a bit further away from the sun than the Earth is.
Last edited by Soralin on Thu Apr 14, 2011 4:21 pm UTC, edited 1 time in total.

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Re: Alternative biochemistries and supercritical fluids

Postby Angua » Thu Apr 14, 2011 4:21 pm UTC

You don't need photosynthesis - think of all the life in the deep ocean vents that don't get any light.
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sociotard
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Re: Alternative biochemistries and supercritical fluids

Postby sociotard » Thu Apr 14, 2011 7:04 pm UTC

Actually Venus is well outside of the Supercritical range for CO2, and while Jupiter and Saturn may and probably do have super critical oceans of hydrogen and helium thats basically all they have with some methane and ethane. But then you get to the fact that they are so cold reactions involving those species don't happen spontaneously and for a metabolic process there is not much to metabolize.
What? Wikipedia said that the Venusian surface was within the critical range. Then again, it was wikipedia. Lets go to more authoritative sources.

My copy of "Perry's Chemical Engineers' Handbook 7th ed" says that the critical temperature for CO2 is 304.31 K and the critical pressure is 7.39 MPa. Those same properties for N2 are 126.2 K and 3.39 MPa

Nasa supplies a fact sheet on Venus.
http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html
This says that the surface pressure is 9.2 MPa and the Average atmospheric temperature is 737 K.

9.2>7.39>3.39, so the venusian surface is above the critical pressure for both CO2 and N2
737>304.31>126.2, so the Venusian atmosphere is above the critical pressure for both CO2 and N2
This site
http://www.datasync.com/~rsf1/vel/1918vpt.htm
says that venus surface temp varies between 673-773 K

So, at all points here, the temperature and pressure are above the critical points. Of course, these are hellish temperatures, so they'd need something more than just substitution of CO2 for H2O, since the protiens and fats we know and love wouldn't last.


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