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Mars is often referred to as a desert world, and for good reason – its surface is barren, dry and cold. While water was abundant in the distant past, it has long since disappeared from the surface, although ice, snow, frost and fog are still common. Other than liquid brines possibly trickling at times, all of Mars’ remaining water is now frozen in permafrost and in the polar ice caps. It has long been thought that the harsh conditions would make current life unlikely at best, and now a new study reaffirms that view.
The results come from continued analysis of the data from the Phoenix lander mission, which landed in the arctic region near the north pole of Mars in 2008. They suggest that Mars has experienced a prolonged drought for at least the past 600 million years.
According to Dr. Tom Pike from Imperial College London, “We found that even though there is an abundance of ice, Mars has been experiencing a super-drought that may well have lasted hundreds of millions of years. We think the Mars we know today contrasts sharply with its earlier history, which had warmer and wetter periods and which may have been more suited to life. Future NASA and ESA missions that are planned for Mars will have to dig deeper to search for evidence of life, which may still be taking refuge underground.”
The team reached their conclusions by studying tiny microscopic particles in the soil samples dug up by Phoenix, which had been photographed by the lander’s atomic-force microscope. 3-D images were produced of particles as small as 100 microns across. They were searching specifically for clay mineral particles, which form in liquid water. The amount found in the soil would be a clue as to how long the soil had been in contact with water. It was determined that less than 0.1 percent of the soil samples contained clay particles, pointing to a long, arid history in this area of Mars.
Since the soil type on Mars appears to be fairly uniform across the planet, the study suggests that these conditions have been widespread on the planet, and not just where Phoenix landed. It’s worth keeping in mind though that soil particles and dust on Mars can be distributed widely by sandstorms and dust devils (and some sandstorms on Mars can be planet-wide in size). The study also implies that Mars’ soil may have only been exposed to liquid water for about 5,000 years, although some other studies would tend to disagree with that assessment.
It should also be noted that more significant clay deposits have been found elsewhere on Mars, including the exact spot where the Opportunity rover is right now; these richer deposits would seem to suggest a different history in different regions. Because of this, and for the other reasons cited above, it may be premature then to extrapolate the Phoenix results to the entire planet, similar soil types notwithstanding. While this study is important, more definitive results might be obtained when physical soil samples can actually be brought back to Earth for analysis, from multiple locations. More sophisticated rovers and landers like the Curiosity rover currently en route to Mars, will also be able to conduct more in-depth analysis in situ.
The Phoenix soil samples were also compared to soil samples from the Moon – the distribution of particle sizes was similar between the two, indicating that they formed in a similar manner. Rocks on Mars are weathered down by wind and meteorites, while on the airless Moon, only meteorite impacts are responsible. On Earth of course, such weathering is caused primarily by water and wind.
As for the life question, any kind of surface dwelling organisms would have to be extremely resilient, much like extremophiles on Earth. It should be kept in mind, however, that these results apply to surface conditions; it is still thought possible that any early life on the planet could have continued to thrive underground, protected from the intense ultraviolet light from the Sun, and where some liquid water could still exist today.
Given Mars’ much wetter early history, the search for evidence of past or present life will continue, but we may have to dig deep to find it.
Life outside of Earth appears to require digging or drilling to find. If life evolved on Mars starting 3.5 billion years ago there is still a prospect it exists in liquid brine above subsurface ice. Europa’s oceans are probably too deep to drill into in the near future. The geysers of Enceladus might be worth checking out with a planetary flyby. Aerogel samples would be interesting to look at.
LC
Just for the record, I don’t think it is impossible for some kind of extremophile type life to still exist on the surface, just less likely than underground. I just saw an article somewhere the other day about new microbes being discovered just inches below the surface in the Atacama desert (I’ll have to find it again). There might be more mositure deeper down, but even a few inches of soil could provide some protection. There are also microbes living inside rocks in the Atacama desert, another form of protection. Also, the Viking results have still not been definitely settled one way or the other imo, still an open question…
Yo Paul, referring to the seventh paragraph:
That’s not entirely correct. Space weathering on the Moon involves a number of processes: collisions of galactic cosmic rays and solar cosmic rays; irradiation, implantation, and sputtering from solar wind particles; as well as bombardment by different sizes of meteorites and micrometeorites.
Certainly, and I am sorry if my comment below is taken to mean differently than problems on or near the surface.
Specifically life can hide just shy of a UV intense surface behind windows of some minerals. Quartz specifically is not a good UV-blocker, but others are. This is how photosynthetic life hides in desert rock of, say, Antarctica, where they can prevent dessication and solar damage both.
I doubt it is enough to get away from the surface oxidation however, you would likely start to find any extant life from an ice sheet down. [Added after posting: Or in brines, lcrowell has a good point there, whatever comes first. Water in any form would buffer massive oxidation.]
My own preliminary take home message differs somewhat, but I will really have to read the study to understand what it is telling us.
– Nevertheless I agree with the overall story of a lifeless surface.
But not because it is arid, since bacteria and lichen are known to survive similar conditions on Antarctica. (Tardigrades have to wait for more moist, so they would be out over geological time.) Instead because of the UV oxidization environment.
– Where I start to deviate is here:
Since the polar region is a persistent, I think, low noise (low soil producing) background, it could well be sampling an average of a global heterogeneous surface by way of Mars’ global dust storms.
More soil production in some locales would mean less in others.
– And I question this:
It is really difficult to disentangle causes of weathering, since the geosphere is so dependent on the biosphere (and vice versa). Pedogenesis, soil formation, is affected by flora and fauna.
I found this in a book on quantitative pedogenesis:
“ORGANISMS AS A SOIL-FORMING FACTOR
Soil scientists do not agree among themselves as to the exact
place of organisms in the scheme of soil-forming factors. Nikiforoff,
Marbut, and others contend that life in general and vegetation in
particular are the most important soil formers. “Without plants, no soil
can form,” writes Joffe in his “Pedology.”* On the other hand,
Robinson, in his discussion of the soils of Great Britain writes:
Vegetation cannot be accorded the rank of an independent variable, since
it is itself closely governed by situation, soil, and climate. And, therefore,
whilst the intimate relationship between natural vegetation and soil cannot be
overlooked, it must be regarded as mainly a reciprocal contract.
Likewise, in all studies of soil-climate relationships, vegetation is
treated as a dependent variable rather than as a soil-forming factor,
because significant changes in climate are always accompanied by
variations in kind and amount of plant life. In the ensuing sections, we
shall attempt to clarify this controversy and to elucidate the exact role
of organisms as soil-forming factors.” [My bold; p 197, “FACTORS OF
SOIL FORMATION – A System of Quantitative Pedology”, Hans Jenny (1994).]
* Of course they mean Earth types of soils, that plants grow in et cetera. But that only makes the disentanglement worse.
Dont worry too much about UV and other ionizing radiation influx on the Martian surface as we have organisms right here on Earth which can withstand the doses estaminated at the Martian surface like http://en.wikipedia.org/wiki/Deinococcus_radiodurans
Its more save to propose the bone-dry Mars if you go with the no life on Mars agenda 😉
Some even say Deinococcus Radiodurans is an invader from Mars as Earth dont have such high radiation environment which could trigger an evolution of this kind of hardiness…
Sure, D. radiodurans can withstand a lot of ionizing radiation due to its capable DNA repair mechanisms. But not UV radiation which breaks down the very repair mechanisms along with everything else biochemical.
Interestingly, this mechanism has been, arguably, found by phylogenetic (trait relationships) methods to have evolved as a defense against dessication. I am out of time to get to the reference, but I am sure you can google it if you are really interested, or maybe it is in that Wp article. You often see the hypothesis that D. radiodurans and its hardy relatives would have evolved to thrive around radioactive environments, but it is found elsewhere too. It does well in deserts, at a guess.
One would expect something like it among putative descendants of martian surface species, as the planet dried up. Likely those would turn up in the uppermost layer of a dig.
I read about how microbes directly protect themselfes from UV by incorporating certain minerals into the cell structure – unfortunatly cant find a link at the moment.
There is certainly alot of research ongoing with poly extremophile organisms but as you stated: UV is easily shielded away by a kind of mineral coating on bacteria colonies for instance or a few centimeter in the soil. UV-reflective rock varnish high in mangenese content could be started with as biomarker.
It is quite interesting that MER Opportunity right now encountered rocks with a kind of coating with very high UV reflectance while it absorbs red to IR wavelengths. Bluish grey UV reflective rock varnish on Mars? 🙂