Is there life on Mars?
Not little green men, of course, but bacterial life. This last week has seen a flurry of stories coming from the Mars Express conference in the Netherlands relating to the possibility of life on the Red Planet. Solid, irrefutable proof isn't here, but a growing number of discoveries are pointing to the very real possibility that the fourth planet in our system may harbor tenacious microbes of its own.
The big announcement this week was the discovery of what seems to be a sea of pack ice frozen just underneath the ground in Elysium Planum. Water ice is by no means unknown on Mars; the planet's north pole is largely covered by it. But Elysium lies just north of the planet's equator, where summertime temperatures can actually come close to 0° C. The ice appears to be covered in ash, protecting it from sublimating away in the thin atmosphere. The coverage also makes the presence of ice hard to confirm through direct observation, and while other theories of what could have caused the unusual formations don't fit the facts as well, only a lander able to drill down through the soil could confirm or refute the hypothesis.
Water -- even water ice -- is necessary for life as we currently understand it. Examples from Earth show that the extreme cold of Mars does not necessarily rule out life's presence, as long as water is available. Extremophile bacteria live in the Antarctic, thriving despite the sub-freezing temperatures. The discovery this week of a microbe frozen for 30,000 years -- then reviving perfectly well when thawed -- suggests a different possibility for bacterial life on Mars. Occasional volcanic activity, solar fluctuations, even meteor hits could warm Mars sufficiently to allow activity and reproduction before the suspended animation microbes settle in again for a long, cold sleep.
Some scientists are going farther than that, however. Some of the evidence from the Mars Express experiments seem to show abundant methane in the Martian atmosphere, more than could be readily explained by non-organic sources. The leader of the team finding the gas, Vittorio Formisano, claims that the atmosphere above Elysium has a particular abundance of methane -- just what one would expect from Martian extremophile bacteria living in the ice. But that's not his most controversial claim. He also asserts that Mars Express has found traces of formaldehyde, created from the oxidation of methane. What was supposedly found would require a substantial amount of methane introduced into the atmosphere on a regular basis, and that could really only come from biological activity. This claim is highly controversial, and even Formisano's teammates are hesitant to endorse his claims.
Even if Formisano's formaldehyde claim turns out to be wrong (and that's a good possibility), this controversy underscores the need to get good biological sensors to Mars. We've been down the path of insufficiently sensitive technology before. When the Viking landers dug through the dirt of Mars in 1976, they found no signs whatsoever of life, just cold, dead ground sterilized by the ultraviolet glare of the sun. But later tests showed that the Viking experiments may have been the problem; the same equipment couldn't detect the sparse but present bacteria in the nearly-lifeless soils of the Atacama desert in Chile. Viking showed that Mars wasn't teeming with life, but not much more than that.
If we do, finally, find microbial life on Mars, it will easily be the greatest scientific discovery of the century, perhaps of history. It's hard to overestimate the importance a non-terrestrial species would have for biology, our understanding of planetary evolution, even philosophy. Perhaps of more interest to WorldChanging readers is the notion that, if we find one species of microbe in the ice of Mars, there's every reason to believe that we'll find more. Evolution would push specialization, and life seems always to find its way to be fruitful, and multiply. We wouldn't just be discovering the first non-terrestrial species, we'd be seeing the first component of a non-terrestrial ecosystem. Simple and spare, to be sure, but a crucial element of a larger understanding of how life and planetary environments co-evolve, not just here, but everywhere.
The big questionin my mind is if Martian life would share the same cellular mechanisms as terran - DNA, RNA, mitochondrial metabolism - or something completely unique and different. Will the panspermists be right?
I think there's a very good chance that any microbes found on Mars will bear a striking resemblance to Earth life. Mars, being smaller, cooled faster than the Earth; that would have allowed water to form there first, too. It's likely that life would get a chance to evolve on Mars before evolving on Earth.
Moreover, Mars during the first billion years or so was hit by quite a few asteroids. We know for a fact that some small but not insignificant percentage of meteorites hitting the Earth are fragments of Mars knocked off by big asteroid hits millions of years ago. It is not at all impossible to imagine Martian microbes, evolving there well before anything had a chance on Earth, getting smacked off the planet and hitting here, "seeding" Earth with Martian life.
On balance, that's probably not the way things happened, but it's definitely a possibility. If we do find microbial life on Mars, however, and it has a DNA/RNA structure markedly similar to our own, that's the most likely explanation.