Curiosity on Mars
NASA’s $2.5 billion mission paid off as Curiosity lands on Mars. Never mind that Google placed the news second behind the latest nut shooting. This is how space was supposed to be–risk all to gain all. The ultimate Olympic team.
What will Curiosity find there? As it happens, during my “vacation” I was reading about microbial colonization in dryland systems. Frank Herbert, we may recall, dedicated Dune to “the dry-land ecologists.” Dryland, arid, or desert is defined not (as you might think) as a place where no rain falls, or where there’s no humidity, but as a place where water evaporates faster than rain falls. The most extreme dryland on Earth, the Atacama desert in Chile, indeed has nearly no rainfall; but the air contains enough water to precipitate fog and dew. The fog off the ocean supports “lithic biofilms” –microbial communities living on or within the rock itself. Microbes called haloarchaea can grow even in the interstices of halite crystals, the most water-sucking habitat known. Now we even find cyanobacteria growing there, conducting photosynthesis while protected from UV.
In fact, the authors note, no matter how dry the landscape on Earth, even the coldest, microbial life finds “oases” within rock. “Thus, it seems that there is no aridity-defined limit to terrestrial life on Earth.” Is there on Mars? Let’s hope Curiosity turns over enough rocks to find out.
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Ultraphyte 
I’ve got my hopes. Something’s bubbling methane into the Martian atmosphere, and I doubt it’s a cow.
The methane is probably primordial, not biogenic. However, one surprise for me is that there has never been a below surface temperature profile developed for Mars. One would think that temperature should rise towards the core, and that at some level it should exceed 0C, thus allowing for liquid water in the the interstices of the rocks, and hence allowing for subsurface microbial life. How deep that would need to be, I have no idea. If there is life, perhaps it is better to look for readily observable minerals.
Heat available on formation will be about equal to mass; Mars has 0.107 * Mass of Earth.
Area available to radiate that heat will be given by the area of an oblate spheroid, but the area of an actual sphere should be close enough; this gives us that Mars has 0.284 * Earth surface area.
If we assume that the conductivity of rocks is roughly constant, and ignore actinide decay heating (Earth is more dense, suggesting that it will contain more actinides and their decay products, and hence benefit more from this), Mars will lose heat some 284/107, or about 2.5 times faster.
Accordingly, it’s safe to assume that the Martian core is way cooler than ours, even if it hasn’t solidified out.
Of course, carbon based life requires a fairly restricted temperature range. Whether life can be based on other organics, say silicon, is another matter.
I think that ignoring actinide decay is probably foolish (at the level of Lord Kelvin foolish), since something provided the heat that pushed out Olympus Mons. However, from what I’ve read, I believe that the lack of a magnetic field precludes a circulating iron core, as does the lack of plate tectonics and (again) the presence of Olympus Mons and the other bits of the Tharsis bulge, which are hypothesized to be what happens when there aren’t plate tectonics, but there is molten rock in the core. I don’t know what temperature iron ceases to be molten at core temperatures and pressures, but I suspect that’s what is at the center of Mars.
That said, as others note below, the surface rises to above freezing during equatorial summers, simply due to insolation, so it’s entirely possible that extremophiles could live at or near the surface. The big problem is that Mars apparently lost most of its flowing water billions of years ago. That’s a long dry stretch for them to endure, even if their cell cycles are measured in centuries. Still, I have my hopes. The one thing about the early loss of plate tectonics on Mars (bilions of years ago) is that there hasn’t been the continual crushing of rocks that we see on Earth, so things could conceivably live in place for that long.
The logic of your sentence 1 is that volcanic activity is caused by actinide decay.
My point was that, simply because Mars is less dense than Earth, it probably contains a lower proportion of actinides, and hence will benefit less from actinide heating. I’m not claiming that ignoring actinide heating is any sort of “good” assumption; just that it’s a better assumption to ignore actinide heating for both planets than to either allow it for one and disallow it for the other, or trying to guess how much of it Mars benefited from without an Aerological composition based on more than surface pebbles.
The way you get around the problem is to do spectroscopic examination of exposed lava flows on Mars, which do exist and have been studied. The other thing to do is to look at Mars as having a smaller core similar to Earth, rather than looking at overall density. If your original question is the temperature profile from surface to core, then assuming that there’s no remnant heat in the core is problematic.
I should point out here that if you do a Google search on “Mars core,” people are working on the question, and there’s a whole paragraph in Wikipedia about the presumed core size and composition of the interior of the planet.
Parts of Mars do thaw in the summer. On earth, even Antarctic glaciers support growth of algae. Furthermore, below-ground microbes are estimated to grow with generation times of hundreds of years. These conditions could well be found on Mars–but the chance of one rover finding the “oasis” are slim.
Is it part of Curiosity’s mission profile to examine the recently discovered Martian brine flows? Seems like a good place to look for extremophiles.
Brine is a good place to look; I think there is a lot of concentrated salt on Mars, so they shouldn’t have trouble finding it.
” The big problem is that Mars apparently lost most of its flowing water billions of years ago.” There are however microbes that grow as endoliths, within the rock. They actually extract the water from the rock crystals.
I’ve seen recent, informed, statements that the size changes in the Martian “frost caps” are at least partly due to melting and freezing of water ice, rather than purely due to sublimation of CO2 as was frequently claimed during the 1970s and 80s.