Simple yet astonishing: life on Mars
Occam’s Razor: Faced with multiple possible explanations, don’t go for the splashiest; choose the simplest – the one that requires the least number of coincidences – the one that is least astonishing.
If the simplest explanation doesn’t pan out, move on to the next simplest (which is also a bit more astonishing).
The leader of the team running an instrument aboard Mars Express – a European Space Agency spacecraft orbiting Mars – believes his data imply something truly astonishing: Martians.
Single-celled, bacterial-type Martians, but life on Mars, just the same.
White light is a mix of all colors; water molecules preferentially absorb red. Dig a hole in the snow and the light coming through the sides looks blue – red has been absorbed, evidence that snow is made of water.
Every substance absorbs a certain combination of colors, giving it a spectral “fingerprint.” Sunlight reflecting off the Meridian Plains of Mars was depleted in the colors absorbed by the mineral hematite. Hematite, on Earth, almost always forms in the presence of water – which is why the rover Opportunity was targeted to land there. (As hoped, Opportunity found lots of evidence that Mars was once wet.).
Analyzing the light reflecting off the surface of a planet is not easy. Hundreds of substances, in the rocks and in the air, absorb numerous colors. The spectrum looks like a rainbow, with hundreds or thousands of dark lines where various colors – hundreds of fingerprints, combined – are missing.
Three teams, working with three different infrared spectrometers – one orbiting Mars, the other two on Earth – believe they’ve seen the fingerprint of methane in the Martian air.
The air on Mars is thin – about as thick as the air 50 kilometers above the surface of the Earth. This, says atmospheric chemist Mark Allen (Caltech), gives us a facsimile of the Martian atmosphere to study, just 25 miles or so above our heads.
Ultraviolet radiation (UV) from the sun would destroy life on Earth’s surface were it not absorbed by oxygen and ozone. Twenty-five miles up, the UV is so intense, it break up molecules – including molecules of methane.
Solar UV should also destroy methane on Mars. But spectroscopists believe they have found it there – not everywhere, but in three specific regions of the planet – some of the same regions where Mars Odyssey has found evidence of underground water. Where is the methane coming from?
In response to a query late last year, I got an e-mail from Vitorrio Formisano – head of the Mars Express spectrometer team – in which he said he was working on a follow-up to the methane discovery but wasn’t ready to talk about it. A couple of weeks ago, he was ready.
Formisano believes he has found the fingerprint of formaldehyde, formed from methane that’s been hit by UV. But formaldehyde is photolysized – destroyed by UV – even faster than methane. To get as much formaldehyde as he sees, the Martian atmosphere must hold a lot of methane – too much, in his view, to be coming from the rocks, or from impacting comets, as others have suggested.
Astrobiologist Rocco Mancinelli (Ames Research Center) counters that we don’t know enough about Martian geology to say that the methane is not coming from the rocks. Both Mancinelli and Allen point out that the spectroscopists are working at (beyond?) the limits of their instrumentation, struggling to detect very small quantities of gases, extracting data from very small amounts of radiation – very dim light.
Earth and Mars draw close again this summer, when we will launch another probe to further investigate the red planet.
Alan Stahler trained as a biologist and is an amateur astronomer. He teaches private enrichment classes for students of all ages. His science programs can be heard at noon on alternate Tuesday on KVMR-FM (89.5).
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