Over the last decade or so, NASA’s Mars Exploration Program has been based on the slogan “follow the water”. The idea is that life as we know it on Earth can survive in pretty much any environment containing liquid water, so finding water is paramount in the search for life on Mars.
Well, the pursuit of water may have come to an end. Today, on sol 25 (that’s a martian day, for those of you looking to increase your geek vocabulary), missions scientists have suggested that Phoenix has found water!
Thanks to Mars’ paper-thin atmosphere (less than 1% as thick as Earth’s), water is not stable on the planet’s surface – it would evaporate away into water vapor. So if, hypothetically, water ice were exposed on the surface, we wouldn’t expect it to stay around for long.
A few sols ago, Phoenix took a picture of the trench it had dug, admiring its own work and providing scientists with an idea of what lies beneath the surface. Inside the trench were white patches and a few apparent clods of soil. The white patches grabbed the most attention: was this the ice Phoenix had been sent to find? Or maybe it was just salt, or light-colored silica like the patch Spirit found a few months ago. Unfortunately, that answer was a few days in the making: planners knew that when Phoenix got around to imaging the trenches a couple days later, water ice would be gone while salt or silica would remain.
The latest set of photos shows that some contents of the trench are gone – just disappeared:
These missing pieces are either water ice, or there are Martian mice scurrying around, gathering pebbles. (Disclaimer for any conspiracy theorists – that was a joke.) Actually, that’s not quite completely accurate, and it’s important to not make too many absolute statements until proper chemical analyses have been done. After all, these “missing clods” could be any solid material that is unstable under conditions on the surface of Mars – any volatile solid unable to withstand the near-vacuum of Mars’ atmosphere. But given orbital detection of water ice and known geochemistry, it certainly seems likely that the finish line in the search for water on Mars may be in sight.
Great post. It made me think of a geeky, sci-fi movie question. I understand the basis of looking for water as a potential foundation of life, but that’s only life as we know it on our planet, with its own atmospheric and geochemical characteristics. Is there reason to believe that life in other systems will be (or is) founded on the same principles and will look the same as ours does, or even defined as life in the same sense as ours? More of a philosophical question than a scientific one, but I think the two are somewhat tied together in this situation.
I’m a bit ignorant here. We know that the poles of Mars seasonally carry lots of white, frozen out CO2, right? Couldn’t this vanishing white material also be CO2 instead of water ice?
Good questions (sorry about the slightly late response…). That’s right, Anna, the entire framework of the search for life is based around the search for Earth-like life. Sure, there could be other types of life out there – from a biochemically similar type that might make use of different amino acids or nucleic acids within the same biochemistry to a system with a completely different solvent. Water seems ideal largely because we’ve done pretty well with it, but it also has key qualities such as its high heat capacity, a less-dense solid phase (which has important implications for global temperature regulations), and its ability to dissolve salts. Father out in the solar system where temperatures are colder and water is frozen, other solvents could be useful – ammonia, dinitrogen, and methyl alcohol have been bandied about, but there are a lot of unanswered questions. Most astrobiologists freely acknowledge the possibility of alien biochemistries and are intrigued by the speculation, but it seems most reasonable to look for what we know (or think we know), especially on Mars where it looks like physic-chemical conditions were similar to those on Earth. If life is a deterministic process (as in, if certain criteria are met, life forms), then we might expect earth like life to form under Earth-like conditions, even on Mars.
Matt, I have a slightly less solid answer for your point. First off, dry ice (solid CO2) precipitates from the atmosphere and generally stays on the surface, so it seems odd (though possible) that it would be found deeper down. During this time of year (Northern summer on Mars), dry ice is not stable at Phoenix latitudes, so unless a patch of ground is perfectly shaded (unlikely given the relatively flat nature of the landing site), the CO2 would not still be present on the surface. Also, the presence of water ice fits well with expectations. Previous neutron counts showed large concentrations of water in the first couple meters of the soil, so that’s hopefully what we’re looking at. To be sure, though, this isn’t proof, and future study will tell us for sure (trite but true).
Most astrobiologists freely acknowledge the possibility of alien biochemistries and are intrigued by the speculation, but it seems most reasonable to look for what we know (or think we know), especially on Mars where it looks like physic-chemical conditions were similar to those on Earth.
While I completely take your point, the standard astrobiology strategy is similar to that of the bloke who is looking for a dollar under a streetlamp because that’s where the light is, even though he thinks he dropped it somewhere else. :)
A problem with biology based on non-aqueous chemistry is temperature. Presumably the first reactions necessary were uncatalyzed by enzymes (before those enzymes evolved). Chemical reaction rates are exponential with temperature and so roughly double with every 10 C temperature increase.
The hottest (known) life is ~120 C. The coldest water based life couldn’t have evolved much below 0 C. It took several billion years to get water based life jump-started. It would likely take multiple times that long at much colder temperatures, even if the chemistry worked.
There very likely is liquid water on Mars, it is just multiple km below the surface. All the hyperthermophilic organisms are autotrophic.