Comments on: Did salt lick Martian life? http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/ I am an astronomer, writer, and skeptic. I likes reality the way it is, and I aims to keep it that way. My real name is Phil Plait, and I run the Bad Astronomy blog. Sun, 05 Jul 2009 05:53:50 +0000 http://wordpress.org/?v=2.3.1 By: Paul Scott Anderson http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-150530 Paul Scott Anderson Fri, 23 Jan 2009 03:19:27 +0000 http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-150530 Again, _some_ of Mars' early water was acidic and salty, not all of it. The newest recent discovery (announced just a few weeks ago) of carbonate deposits is yet more evidence of that, as was discussed by the scientists themselves. Why can't some people understand that what has been found by the rovers in two tiny areas cannot necessarily be extrapolated to the entire planet? The evidence from the orbiters continues to indicate a variety of conditions in the past, just like on Earth. Paul The Meridiani Journal a chronicle of planetary exploration web.me.com/meridianijournal Again, _some_ of Mars’ early water was acidic and salty, not all of it. The newest recent discovery (announced just a few weeks ago) of carbonate deposits is yet more evidence of that, as was discussed by the scientists themselves. Why can’t some people understand that what has been found by the rovers in two tiny areas cannot necessarily be extrapolated to the entire planet? The evidence from the orbiters continues to indicate a variety of conditions in the past, just like on Earth.

Paul

The Meridiani Journal
a chronicle of planetary exploration
web.me.com/meridianijournal

]]> By: Mars methane media mess | Bad Astronomy | Discover Magazine http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-150073 Mars methane media mess | Bad Astronomy | Discover Magazine Wed, 21 Jan 2009 19:41:01 +0000 http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-150073 [...] is pretty different than here; the water that once flowed on its surface was probably acidic and very salty, and when it dried up left weird things like jarosite. Not only that, there appears to be [...] […] is pretty different than here; the water that once flowed on its surface was probably acidic and very salty, and when it dried up left weird things like jarosite. Not only that, there appears to be […]

]]> By: Tangled Bank #99! « PodBlack Blog http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-70699 Tangled Bank #99! « PodBlack Blog Thu, 21 Feb 2008 07:47:11 +0000 http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-70699 [...] Astronomy - Did salt lick Martian life? [...] […] Astronomy - Did salt lick Martian life? […]

]]> By: Paul Scott Anderson http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-70698 Paul Scott Anderson Wed, 20 Feb 2008 05:35:51 +0000 http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-70698 It should be remembered that there is still the evidence for earlier, less acidic (and less salty?) water, which left behind the clay mineral deposits, documented by Mars Express. Ray Arvidson of the MER team mentioned this again in this recent December 10, 2007 update: http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html "We see evidence from orbit for clay minerals under the layered sulfate materials," said Ray Arvidson of Washington University in St. Louis, deputy principal investigator for the rovers' science payload. "They indicate less acidic conditions. The big picture appears to be a change from a more open hydrological system, with rainfall, to more arid conditions with groundwater rising to the surface and evaporating, leaving sulfate salts behind." I've commented about this on the blog, also. Paul The Meridiani Journal a chronicle of planetary exploration web.mac.com/meridianijournal It should be remembered that there is still the evidence for earlier, less acidic (and less salty?) water, which left behind the clay mineral deposits, documented by Mars Express. Ray Arvidson of the MER team mentioned this again in this recent December 10, 2007 update:

http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20071210a.html

“We see evidence from orbit for clay minerals under the layered sulfate materials,” said Ray Arvidson of Washington University in St. Louis, deputy principal investigator for the rovers’ science payload. “They indicate less acidic conditions. The big picture appears to be a change from a more open hydrological system, with rainfall, to more arid conditions with groundwater rising to the surface and evaporating, leaving sulfate salts behind.”

I’ve commented about this on the blog, also.

Paul

The Meridiani Journal
a chronicle of planetary exploration
web.mac.com/meridianijournal

]]> By: TheBlackCat http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-70697 TheBlackCat Mon, 18 Feb 2008 23:06:10 +0000 http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-70697 And before you start arguing about the importance of entropy, I only brought it up because I knew it is a common misconception that hydrophobicity is driven by enthalpy. You need to use entropy if you start getting into a detailed quantitative analysis of protein folding (or folding of any macromolecule) but if you understand its importance then what matters for a qualitative analysis is the relative solubility in different substances. And before you start arguing about the importance of entropy, I only brought it up because I knew it is a common misconception that hydrophobicity is driven by enthalpy. You need to use entropy if you start getting into a detailed quantitative analysis of protein folding (or folding of any macromolecule) but if you understand its importance then what matters for a qualitative analysis is the relative solubility in different substances.

]]> By: TheBlackCat http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-70696 TheBlackCat Mon, 18 Feb 2008 21:46:58 +0000 http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-70696 No need to worry about entropy, the solubility of hydrophobic chemical in ammonia relative to water can be directly measured, and has been. Ammonia dissolves polar chemical well, but not as well as water, while it dissolves nonpolar chemicals poorly, but significantly better than water. This is exactly the problem I was describing. http://www.infoplease.com/ce6/sci/A0856597.html No need to worry about entropy, the solubility of hydrophobic chemical in ammonia relative to water can be directly measured, and has been. Ammonia dissolves polar chemical well, but not as well as water, while it dissolves nonpolar chemicals poorly, but significantly better than water. This is exactly the problem I was describing.

http://www.infoplease.com/ce6/sci/A0856597.html

]]> By: Tom Marking http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-70695 Tom Marking Mon, 18 Feb 2008 18:34:21 +0000 http://blogs.discovermagazine.com/badastronomy/2008/02/15/did-salt-lick-martian-life/#comment-70695 "Here are some sources: http://mrw.interscience.wiley.com/emrw/9780470015902/els/article/a0003002/current/abstract http://mrw.interscience.wiley.com/emrw/9780470015902/els/article/a0002975/current/abstract http://www.rsc.org/Publishing/Journals/CP/article.asp?doi=b404327h " The first two articles are pay-per-view (or free if you are a member of the web site) so I didn't delve into them. But based on their titles they appear to be dealing exclusively with proteins in aqueous solution. The third article entitled "Entropy/enthalpy compensation ..." also deals exclusively with water as a solvent. The word ammonia is not found one time in the article so there is obviously no comparison of water versus ammonia. So this is hardly convincing evidence that water is the only possible solvent for any organic macromolecule. Since there are quadrillions of possible organic macromolecules only a small fraction have ever been studied in earthly laboratories. I have managed to find some obvious comparisons of the two molecules however: http://en.wikipedia.org/wiki/Water_molecule Water molecule: bond length = 95.84 picometers bond angle = 104.45 degrees http://en.wikipedia.org/wiki/Ammonia Ammonia molecule: bond length = 101.7 picometers (6 percent more than water molecule) bond angle = 107.8 degrees (3 percent more than water molecule) http://www.ualberta.ca/~jplambec/che/data/p00403.htm Water: Delta-enthalpy of formation (DH0f) = -241.818 kJ/mole Delta-Gibbs energy of formation (DG0f) = -228.572 kJ/mole Entropy (S0) = 188.825 kJ/mole Heat capacity at constant pressure (C0p) = 33.577 Ammonia: Delta-enthalpy of formation (DH0f) = -46.11 kJ/mole Delta-Gibbs energy of formation (DG0f) = -16.45 kJ/mole Entropy (S0) = 192.45 kJ/mole Heat capacity at constant pressure (C0p) = 35.06 Thus, the entropy for ammonia is only 2 percent different than the entropy of water. Wasn't this supposed to be the defining property of the water molecule, its supposed huge entropy? Well, ammonia's is two percent higher. The only substantial differences between water and ammonia in terms of thermodynamic properties appears to be in their enthalpies of formation. It takes five times as much energy to break a water molecule into its constituent atoms as it does for ammonia. But since you never mentioned that particular point I don't think its relevant to your argument. “Here are some sources:
http://mrw.interscience.wiley.com/emrw/9780470015902/els/article/a0003002/current/abstract
http://mrw.interscience.wiley.com/emrw/9780470015902/els/article/a0002975/current/abstract
http://www.rsc.org/Publishing/Journals/CP/article.asp?doi=b404327h
”

The first two articles are pay-per-view (or free if you are a member of the web site) so I didn’t delve into them. But based on their titles they appear to be dealing exclusively with proteins in aqueous solution. The third article entitled “Entropy/enthalpy compensation …” also deals exclusively with water as a solvent. The word ammonia is not found one time in the article so there is obviously no comparison of water versus ammonia. So this is hardly convincing evidence that water is the only possible solvent for any organic macromolecule. Since there are quadrillions of possible organic macromolecules only a small fraction have ever been studied in earthly laboratories.

I have managed to find some obvious comparisons of the two molecules however:

http://en.wikipedia.org/wiki/Water_molecule
Water molecule:
bond length = 95.84 picometers
bond angle = 104.45 degrees

http://en.wikipedia.org/wiki/Ammonia
Ammonia molecule:
bond length = 101.7 picometers (6 percent more than water molecule)
bond angle = 107.8 degrees (3 percent more than water molecule)

http://www.ualberta.ca/~jplambec/che/data/p00403.htm
Water:
Delta-enthalpy of formation (DH0f) = -241.818 kJ/mole
Delta-Gibbs energy of formation (DG0f) = -228.572 kJ/mole
Entropy (S0) = 188.825 kJ/mole
Heat capacity at constant pressure (C0p) = 33.577

Ammonia:
Delta-enthalpy of formation (DH0f) = -46.11 kJ/mole
Delta-Gibbs energy of formation (DG0f) = -16.45 kJ/mole
Entropy (S0) = 192.45 kJ/mole
Heat capacity at constant pressure (C0p) = 35.06

Thus, the entropy for ammonia is only 2 percent different than the entropy of water. Wasn’t this supposed to be the defining property of the water molecule, its supposed huge entropy? Well, ammonia’s is two percent higher. The only substantial differences between water and ammonia in terms of thermodynamic properties appears to be in their enthalpies of formation. It takes five times as much energy to break a water molecule into its constituent atoms as it does for ammonia. But since you never mentioned that particular point I don’t think its relevant to your argument.

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