Odds of Life
Here's what scientists know. Analyses have confirmed that enigmatic
streaks that appear in summertime on the planet's slopes are produced by
liquid water—salty water, perhaps capable of sustaining chemical
reactions and even life.
Like Mars itself, the dark watery streaks are ruggedly beautiful, as seen in photographs taken by the HiRISE camera aboard the
Mars Reconnaissance Orbiter. But for all their picturesque drama, these dark marks represent more of a trickle than a flow.
It’s possible they’re fed by some kind of underground aquifer, or a
buried icefield that thaws in warmer weather and sends melted Mars water
sliding downhill.
While not outside the realm of possibility—we do know
there’s ice buried beneath the Martian surface—such
scenarios aren’t as likely as the one scientists favor: The water comes
from the atmosphere. If that's true, it’ll be a much tougher resource
to tap into.
But how could water from the atmosphere form these dark streaks? On
Mars, as on Earth, salts on the surface can absorb atmospheric water
vapor and trap it in their crystal structures. Then, when the soggy
crystals warm up, they dissolve. The whole liquidy mix surrenders to the
tug of gravity, and off it goes, tumbling downhill.
In Chile’s super-dry Atacama desert, this exact type of system—called deliquescence—is the key to supporting
some rather extreme life, says NASA astrobiologist
Chris McKay.
But there’s no guarantee this is happening on Mars. McKay notes that
the type of salts near the Martian streaks, called perchlorates, form
different watery mixtures than the salts we’re most used to on Earth. In
fact, it’s possible the perchlorate streaks could behave similarly to
Antarctica’s
Don Juan Pond, which is the saltiest liquid water body on Earth—and totally dead.
“Such a brine is not suitable for life and is of no interest
biologically,” McKay says. “Nothing can live in the brine of Don Juan
Pond.”
Follow the Water
So, seeps fueled by atmospheric humidity might not make the most
convenient water well for human colonists, and they might not even be
ideal habitats for Martian microbes—but wouldn’t it be worth finding
out?
Of course. What we know so far, based on the single example of Earth,
is that life tends to show up wherever there’s water. That’s why NASA’s
search for life beyond Earth has been driven by the mantra, “
Follow the water.”
The frustrating irony here is that NASA can’t follow this particular water. Not yet.
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