The Heavens. Once an object of superstition, awe and fear. Now a vast region for growing knowledge. The distance of Venus, the atmosphere of Mars, the size of Jupiter, and the speed of Mercury. All this and more we know. But their greatest mystery the heavens have kept a secret. What sort of life, if any, inhabits these other planets? Human life, like ours? Or life extremely lower in the scale. Or dangerously higher.~ Richard Blake, and William Cameron Menzies, Narrator, "Invaders from Mars" (1953).
The search for life on Mars may just have been too shallow all these years.
All our probes and rovers have been scratching at the surface since the Viking landers arrived 30 years ago. Of course, ever since Mariner returned pictures of Mars that showed a moon-like surface, scientists lost confidence that we were going to see any purple giraffes walking by, so efforts turned to finding evidence of microbial life, past or, preferably, present.
Viking did look for things that might be scooting around in the Martian dirt, but the results came up mixed. Recently,though, there's been some thinking that perhaps we were wrong in our interpretation of Viking data or that a key instrument might have missed signs of life. Now there's a theory that Viking didn't dig deep enough.
The problem is radiation. We Terrans are lucky to have a world with a pronounced magnetic field that protects us from a great deal of radiation from space. Martian microbes aren't so lucky, as their planet is bathed in all manner of bad dosages. Now that doesn't necessarily negate the possibility of life on Mars, as microbes have been found growing in nuclear reactors, but it definitely is a negative factor.
According to the analysis in the article from Science Blog, we might have to look several meters below the surface to find living things. According to the team, the best place to look that is accessible is in icy rock, which is the environment most likely to harbor life relatively close to the surface. They also suggest a target: Elysium. Elysium is particularly attractive because it may also have underground water.
Searching for water has been a priority since the first Mars rover landed, and, so far, everything suggests Mars had flowing water at some time in the past. Now that evidence suggests water still exists, that is the sort of location to zero in on.
While we're looking, we might also look for Mars' atmosphere. For years, the prevailing theory was that the atmosphere of the Red Planet simply frittered away into space. If you accept the idea that there was once a warm, wet Mars, you would require an atmospheric pressure of 1 to 5 bars, which isn't much, but it's a lot more than the .008 bars present today. But according to this story, Mars Express data shows a loss rate that is too slow to account for that much of a drop in pressure. So where did the atmosphere go?
One theory that's been around for a while is that something large impacted or nearly impacted Mars at one time, ripping much of the atmosphere away. The problem is that there's no evidence of an impact by a six-mile wide object, which one would expect on a world covered with craters. At the least, there would be some sort of debris hanging around, in the form, perhaps of a more substantial satellite than either Phobos or Deimos.
It's possible that the atmospheric loss has slowed over time, but that would assume that the solar wind, which is responsible for much of the removal process, had changed significantly, which seems unlikely. What is left is the idea that the atmosphere is still there on the planet somewhere.
While that sounds sort of odd, apparently some scientists think that there could be a sort of reservoir under the Martian surface. Another alternative, not expressed in the article, is that the atmosphere might be bound to the Martian soil in some manner. Either way, it's still there, waiting to be discovered and perhaps liberated once again.
Either way, the idea increases the odds of life having evolved, which would mean that it's traces are there to be found somewhere. Or, if we dig a little deeper, it may still be crawling around to find.
The next probe needs to have a serious drilling rig.