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The question of whether present-day Mars could be habitable, and to what extent, has been the focus of long-running and intense debates. The surface, comparable to the dry valleys of Antarctica and the Atacama desert on Earth, is harsh, with well-below freezing temperatures most of the time (at an average of minus 63 degrees Celsius or minus 81 Fahrenheit), extreme dryness and a very thin atmosphere offering little protection from the Sun’s ultraviolet radiation. Most scientists would agree that the best place that any organisms could hope to survive and flourish would be underground. Now, a new study says that scenario is not only correct, but that large regions of Mars’ subsurface could be even more sustainable for life than previously thought.
Scientists from the Australian National University modeled conditions on Mars on a global scale and found that large regions could be capable of sustaining life – three percent of the planet actually, albeit mostly underground. By comparison, just one percent of Earth’s volume, from the central core to the upper atmosphere, is inhabited by some kind of life. They compared pressure and temperature conditions on Earth to those of Mars to come up with the surprising results.
According to Charley Lineweaver of ANU, “What we tried to do, simply, was take almost all of the information we could and put it together and say ‘is the big picture consistent with there being life on Mars?’ And the simple answer is yes… There are large regions of Mars that are compatible with terrestrial life.”
So it seems that while, as we know, the surface of Mars is quite inhospitable to most forms of life (that we know of) except perhaps for some extremophiles, conditions underground are a different matter. It is already known that there are vast deposits of ice below the surface even near the equator (as well as the polar ice caps of course), so there could be liquid water a bit deeper where it is warmer. Those conditions would be ideal for bacteria or other simple organisms. While that idea has been proposed and discussed before, Lineweaver’s findings support it on a planet-wide basis – previous studies tended to focus on specific locations in a “piecemeal” approach, but these new ones take the entire planet into consideration.
The paper is currently available for free here. Abstract:
We present a comprehensive model of martian pressure-temperature (P-T) phase space and compare it with that of Earth. Martian P-T conditions compatible with liquid water extend to a depth of *310 km. We use our phase space model of Mars and of terrestrial life to estimate the depths and extent of the water on Mars that is habitable for terrestrial life. We find an extensive overlap between inhabited terrestrial phase space and martian phase space. The lower martian surface temperatures and shallower martian geotherm suggest that, if there is a hot deep biosphere on Mars, it could extend 7 times deeper than the *5km depth of the hot deep terrestrial biosphere in the crust inhabited by hyperthermophilic chemolithotrophs. This corresponds to *3.2% of the volume of present-day Mars being potentially habitable for terrestrial-like life. Key Words: Biosphere—Mars— Limits of life—Extremophiles—Water. Astrobiology 11, xxx–xxx.
Up to 310 kilometres, but at what depth do the correct temperature/pressure conditions *start*? 10 metres? 100? 1000? If the habitable zone starts more than a few dozen metres underground, it’s just as inaccessible to us as Europa’s oceans, or Titan’s proposed water/ammonia mantel.
Like, er… click on the above link to download the paper and all will be revealed, man.
I plan to do that:P. I was pressed for time yesterday and couldn’t read the paper.
Besides the obvious question, my previous post was intended to (gently) imply that the article was lacking. A summary article should hit all the key points of the paper that it’s summarizing. This article failed to do that.
You critique grammar and spelling, I critique journalistic style;).
Fair enough. 😉
When I had pretty much finished the article, the paper still wasn’t available yet, except through a paywall. Many other space web sites and blogs were already writing about this as well, without the paper yet. So I did the article, but then when the paper did become available, I was able to provide a link to it at the end.
Thanks for taking the time to explain:).
Figure 1 puts conditions for liquid water up to the surface. This should mean there are conditions acceptable for some form of life just under the surface where UV and other radiation would not damage living systems.
LC
I personally expect microbes to be discovered elsewhere in our solar system, however most likely not evolved in situ, but present by contamination from earth meteorite ejecta or other means.
The one thing which gives me some optimism about the contamination problem is that I suspect any life form on Earth is not likely to survive the radiation and harsh environment on the Martian surface. If life started out on Mars then maybe it has evolved to exist in a subterranean (submaritan) environment, and the actual surface may be completely sterile.
If we find life on Mars its genome, or genomes for some range of species, will be sequenced and compared to life on Earth. If matches are sufficiently close to Earth genes we might suspect cross-fertilization between the planets. We might also do some experiment to expose Earth prokaryotes to a Martian environment at the surface to determine if any can survive. A simulated environment on Earth would likely suffice.
LC
Personally I don’t view this kind of contamination, if it exists, as a problem. I tend to view it as very natural, given the possibility that life on Earth perhaps did not begin here.
Regarding the harsh surface of Mars, agreed, however it seems that methods of transfer ( in significant events, at least) would have the potential to pickup organism from below our surface and inoculate them well below the surface of Mars. Or vice versa, perhaps Mars is the original contaminator.
The problem is with trying to determine if life found on Mars is indigenous to Mars or a transplant. A piece of Earth could well have been kicked into space by an asteroid impact which then found its way to Mars. I suppose we will never be able to absolutely determine whether life found on Mars was not transplanted from Earth hundreds of millions of years ago. So the problem is a scientific one.
LC
The likelihood that we can’t tell whether life is related or not is minute.
The existence of a UCA (Universal Common Ancestor) is the best observed fact in all of science, with an accumulated uncertainty of ~ 10^-2040 (!). (Also here.)
As long as a protocell has evolved a bit of genetic machinery during the RNA world genetic takeover, it would tell of relatedness. The codon assignment is suspected to be a frozen accident, a good but not optimal choice for robustness based on among other things physical characteristics of naturally occurring amino acids. Anyway, there is leeway and we can tell differences. (Say, mitochondria has evolved a slightly different variant of genetic code.)
I have argued elsewhere here that the time period from a prebiotic world to the RNA/DNA world is short, some 40 Ma at most. But even if that estimate is wrong, non-genetic protocells are completely dependent on their environment. They would need to be provided much the same nutrients elsewhere, since their protometabolism isn’t yet adaptable in situ (in the protocell).
So transfer of non-genetic protocells is not a very likely process. And if it happened, it is more akin to transfer of chemically evolved systems to an environment of similar chemically evolved systems than transfer of genetic populations to environments devoid of similar populations.
You didn’t do it in this thread since you noted the genetic tests, but in general I find the plaint that we can’t tell between abiogenesis sources a lazy one. These plaints are never shored up by research or even analysis.
If life is found on Mars I am sure these microbes will be genetically sequenced. I am presuming they will be based on RNA/DNA. These sequences can be then used to try to find some clade with life on Earth. If that is found it is highly probable that there is a connection with Earth biology. If there is no statistical correlation then that is not probable, but it can’t be ruled out. It is the usual aspect of science where a negative can be proven, or nearly proven, but the positive is always more uncertain. If a clade is not found that does not completely rule out some connection between Terrain and Maritian life back 3 to 3.5 billion years ago.
LC
Aussie, Aussie , Aussie, Oye, Oye, Oye!
It is a rather impressive piece of work, pulling together a lot of data to elucidate a difficult but useful question.
However I don’t like some of their optimism.
For example, they note that “If life can survive temperatures of 250 deg C (e.g., in terrestrial hydrothermal vents, Martin et al., 2008), then the martian biosphere could extend to ~ 61km from the average geotherm in Fig. 1.” However I can’t find any direct support in Martin et al.
What Martin et al seems to be describing is how hydrothermal vents fluids can reach ~ 300 deg C while producing reduced-carbon nutrients. “In the hot (>350°C) conditions of black smokers, carbon that is in equilibrium with water, even in the presence of significant levels of H2, usually occurs as CO2. As temperatures decrease to 150°C or lower, as at the LCHF, reduced-carbon species are favoured57,58.”
Of course they should point out the maximum possible biosphere volume. But organisms surviving ~ 250 deg C would cope with twice the current record, organisms that survive ~ 130 deg C (and procreate below ~ 120 deg C). That is a big pill to swallow.
It would also only mean a doubling of the maximum potential biosphere. That the martian crustal biosphere would go ~ one order of magnitude deeper than on Earth, ~ 40 km instead of ~ 2-5 km, is already a good result!
For our crustal life lovers out there, here is an interesting new biotope highly pertinent to this question:
“A team of scientists from Oregon has collected microbes from ice within a lava tube in the Cascade Mountains and found that they thrive in cold, Mars-like conditions.
The microbes tolerate temperatures near freezing and low levels of oxygen, and they can grow in the absence of organic food. Under these conditions their metabolism is driven by the oxidation of iron from olivine, a common volcanic mineral found in the rocks of the lava tube. These factors make the microbes capable of living in the subsurface of Mars and other planetary bodies, the scientists say.
[…]
“This reaction involving a common mineral from volcanic rocks just hasn’t been documented before,” said Martin Fisk, a professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences and an author on the study. “In volcanic rocks directly exposed to air and at warmer temperatures, the oxygen in the atmosphere oxidizes the iron before the microbes can use it. But in the lava tube, where the bacteria are covered in ice and thus sheltered from the atmosphere, they out-compete the oxygen for the iron.”
The last part explains why this metabolism isn’t easily observed on Earth, oxidization by atmospheric oxygen competes too strongly. Still some ordinary bacteria find it worthwhile to exploit it under near enough anaerobic conditions.
Olivine has been observed to be extensive on Mars.
The controversial methane in Mars atmosphere, if it exists, would have as source crustal living cellular life forms. Or active volcanism supporting crustal living cellular life forms. Or serpentinization, of which olivine is a major source and now known to support crustal living cellular life forms.
This is a win-win-win scenario!