Methane concentrations revealing a plume in Mars' northern
hemisphere during its summer season. Credit: NASA

We've known about the existence of methane gas on Mars for several years now, from independent observations.  Further observations have led to the detection of "plumes" or clouds of methane gas apparently emanating from specific locations on Mars.  One plume is estimated to contain 19,000 metric tons of the stuff.

Why is this exciting news? If you know anything about the source of most of Earth's atmospheric methane gas, you already know the answer:  possible life.  Not, I should say, necessarily life on Mars, but maybe a strong piece of evidence in that direction.

On Earth, methane (CH₄) is produced by living organisms—mostly by the activity of microbes, but some by the digestive processes in larger organisms (yes, like humans, and cows).  Methane is the major constituent of natural gas, which fuels gas powered ovens and heaters in homes, as well as natural gas power plants.  Methane is also produced by decaying organic matter—that's where "swamp gas" comes from.

On Mars, methane gas cannot exist for long in the atmosphere; it is relatively quickly broken down by solar radiation.  So, the methane detected in Mars' atmosphere must be replenished by something, continually.

So the big question right now is, where is the methane coming from? Under the surface of Mars, almost certainly.  By biological processes—life—underground? Could be.  By non-biological means? Could be, too; methane can be produced through inorganic chemical processes.  We don't know yet.  The next step in finding out more will be the Mars Science Laboratory, a large rover scheduled to be launched to Mars sometime in the near future.

In one form or another, humans have been trying to see, or find, life on Mars for a long time.  Percival Lowell squinted at Mars' small, blurry disk through his 24-inch telescope in Flagstaff, and perceived markings he saw to be vast canal complexes, ostensibly built by a desert Martian civilization thirsty for water harvested from their planet's polar ice caps. This led to much of the science fiction relating to life on Mars in the 20^th Century.

Earth-bound telescopes noted seasonal changes in Mars' color and brightness, and some attributed this to possible seasonal growth of Martian vegetation—though it was later found that these variations were the effects of seasonal planet-wide dust storms.

The Viking landers' primary mission in the 1970's was to search for life.  They didn't find any by scratching around Mars' surface and testing the soils there.

The 1990's saw the controversy over microscopic structures in meteorites found on Earth but determined to have originated on Mars.  Some argued that these structures were fossils of Martian microbes that lived on Mars long ago.  Whether these findings were in fact fossils and not just geologic structures was never conclusive.

The determination that liquid water once flowed on the surface of Mars, and still exists under its surface at least as ice, is pretty much scientific fact today.  Evidence of past liquid flows have been imaged and mapped from space, and the Phoenix lander found water ice in the north polar regions last year.  And there's the rover Opportunity that has confirmed gray hematite, a mineral that forms in the presence of water.

It's almost certain that there are no Martian cows grazing the rusty desert plains out there.  But there seems to be a lot of evidence for the possibility that something is going on below Mars' surface—perhaps the presence of liquid water, perhaps the presence of some form of life.  We don't know yet, but it sure feels like we're onto something here….

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The ‘Snow White' excavation trench, after rasping
and digging by Phoenix. Credit: "NASA/Mars Phoenix"

Since witnessing the historic landing of NASA's Mars Phoenix Lander on May 25, I've been holding my breath to learn if Phoenix has made the discovery it set out to make: whether it landed on a vast deposit of water ice near Mars' northern polar cap.

It took several weeks after landing for the declaration to finally be made-and without further ado, YES, definitely, water ice was found by Phoenix. But even now, in August, it seems the declaration of Phoenix's great discovery is still in the process of unfolding, one careful and tantalizing announcement after another.

From a lay point of view one might think, why did it take weeks for Phoenix scientists to announce that, yes, the white stuff scraped up by the lander's instruments, from under a thin topping of soil, is water ice? And why do there seem to be unanswered questions about the nature of that ice even now, three months after landing?

For those familiar with how a remote robot probe like Phoenix makes its investigation, this is not surprising at all. In fact, serious scientific measurements by Phoenix didn't happen immediately after landing. The mission team had a lot of work to do to make sure the spacecraft was healthy and undamaged, ready to explore.

Then, the team worked Phoenix's robot arm and soil scooper to dig, scrape, and eventually scoop up soil and bits of the white substance and drop it into Phoenix's onboard laboratory compartments. At first, there wasn't much of the white substance included in the scooped up samples. Then, the sample stuck to the scoop. So, just getting an adequate sample into the spacecraft where it could be analyzed wasn't a simple matter of scoop and dump….

Eventually, though, the white substance was identified as water ice. The first clue came when the white substance was exposed to the air and sunlight after being dug up, when it began to slowly disappear: it sublimated (went directly from its solid state to a gaseous state, without passing through a liquid state, without passing Go and collecting $200…). If the white substance were, say, a type of salt, it wouldn't have done that.

Inside Phoenix's chemical laboratories, more definitive tests were performed. One instrument is essentially a small oven in which a sample is slowly heated and any gases that boil off (excuse me: sublimate) are identified by a gas analyzer.

But there were still plot complications! One is the possible detection of the chemical "perchlorate" in the ice sample: an oxidizing ion (a compound of chlorine and oxygen) which, if it does turn out to exist in the Martian ice, will give scientists new food for thought on Martian chemistry and the implications for possible Martian life. It wouldn't rule out the possibility of life (past or present), but is an additional factor in the equation.

So, the search for life on Mars-the big-picture-reason we've been looking for water there-goes on. We have to keep in view the fact that finding microbial life, or fossils thereof, on Mars isn't as simple a matter as snapping a picture and looking for plants and animals; it's more like a 19^th Century story I heard of where a race of mile-high beings from Jupiter land on Earth, and at first don't realize there is life here, under their feet….

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