Alan Stahler: Martian mysteries
June 13, 2018
You show up for work in the morning, to a pleasant surprise: A dish of dark chocolate sits on the front desk. You take a few pieces, figuring they'll all soon be gone.
But when you walk past the desk a few hours later, the dish is full … someone must be re-filling it.
Rocks and soil hold an immense amount of iron and carbon — both of which "want" to combine with oxygen (iron rusts, carbon burns). With enough iron and carbon to gobble up all the oxygen in the air, there should not be any oxygen left for us to breathe.
Fortunately, plants on land, algae and bacteria in the waters, continually replenish the oxygen.
Another gas should not last long in the air: Methane, the gas we cook with if we're plugged into the pipeline. When methane meets oxygen — even without fire — the gases trade atoms, making carbon dioxide and water. Both the methane and the oxygen disappear. Since we find methane in the air, it too must be replenished.
Orbital motions are bringing Earth and Mars closer, night by night. Mars will be super-close, super-bright, in the sky in late July.
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Mars has an atmosphere — thin, but an atmosphere, nonetheless. And in that atmosphere: a trace of methane … which should not be there. Something on Mars must be pumping out methane.
We think of methane as fuel. Combining with oxygen, it yields energy and waste gases: carbon dioxide and water.
But in an oxygen-free environment, a different reaction takes place. Carbon dioxide combines with hydrogen to yield energy and a waste gas. The waste gas, now, is methane.
Something like 95 percent of the methane in Earth's atmosphere is produced by microbes living anaerobically (without oxygen), in animals' guts (from which it escapes, sometimes embarrassingly), and beneath the mud, producing swamp gas.
But the remaining five, maybe 10 percent is produced abiotically — without life — by reactions in rock. (When rock in the ocean floor is squeezed and cooked, some of its minerals metamorphose into serpentine, a green mineral common here in the foothills. The reaction releases hydrogen.)
Where is the gas coming from?
Mars has no life (that we know of) so we have to presume that Martian methane is made in the rocks. A clue was discovered by the Martian rover Curiosity, and published last week in Science: the methane in the Martian atmosphere cycles up and down, peaking toward the end of summer in the northern hemisphere.
This leads to the possibility that the methane is trapped in sub-surface ice, and released when the ice warms up.
But even if that turns out to be the case, it begs the question, "Where did the methane come from in the first place?" Could there once have been Martians — microbial Martians — that made the methane, and then disappeared, billions of years ago, when Mars evolved into its icehouse climate?
Since we first landed a spacecraft on Mars, in the mid-1970s, we've looked for signs of life — especially for molecules that at least resemble molecules made by living things. But the search has come up empty … surprising, because such molecules rain down, all the time, in space dust and meteorites (you don't need life to make such molecules).
There's now good evidence that the surface of Mars, blasted by radiation, quickly destroys such molecules.
In last week's issue of Science was another paper reporting results from Curiosity, this time the finding of these sorts of molecules — not on the surface, but in material retrieved by a drill that bored down two inches beneath the surface.
Curiosity was recently knocked out by a gigantic dust storm that is enveloping the red planet. However, officials said Wednesday they're hopeful the rover, which has been working for the past 15 years, will survive the storm.
In 2020, a spacecraft will again launch toward Mars. The search for Martians — past or present — will continue.
Alan Stahler enjoys sharing his love of nature with students of all ages. His science stories can be heard on KVMR-FM (89.5 MHz), and he may be reached at firstname.lastname@example.org
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