Mars Phoenix: Is It Ice Yet?

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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