Investigation of an ancient Martian meteorite has re-fueled a debate about evidence of possible past life on Mars.
A team of NASA scientists studying the meteorite Y000593, one of a growing number of meteorites chemically identified as having originated on Mars, has reported finding structural and compositional features that may have been formed by biological processes. The tantalizing features include micro-tunnel structures permeating the rock that resemble structures found in Earth basalts modified by the action of bacteria, and microscopic spherules sandwiched between rock layers that contain a richer concentration of carbon than in surrounding layers.
Analysis of Y000593 tells a story of its formation 1.3 billion years ago in a Martian lava flow, and of its forced ejection from Mars 12 million years ago by a major impact event. About 50,000 years ago the tale of this rock's interplanetary voyage ended when it fell onto the Yamato Glacier in Antarctica, where it was discovered by a Japanese research expedition in 2000.
The findings were published in the February issue of Astrobiology, authored by Lauren White of NASA/JPL with co-authors Everett Gibson, Kathie Thomas-Keptra, Simon Clemett and the late David McKay (NASA/Johnson Space Center). In 1996, members of the same team announced that they had discovered features of possible biogenic origin in another Martian meteorite, ALH84001. In both cases the authors are cautious in pointing out that they cannot rule out non-biological processes to account for the features--but in the light of other evidence from robotic missions indicating more Earthly conditions in Mars' past the argument for Martian life is compelling.
Exploration of Mars by robots with capable arrays of scientific instruments has painted a detailed picture of a warmer, wetter environment on Mars long ago. As we learn more about how Earth-like the Martian environment may once have been, and also how quickly life first appeared and thrived in Earth's primordial oceans, the question of life on Mars becomes ever more poignant.
One thing that no robotic mission has yet achieved is the return of Martian rock and soil samples to Earth for detailed laboratory analysis. So meteorites of Martian origin like Y000593 and ALH84001 represent a wealth of geological and chemical information that we presently cannot obtain in any other way. NASA has a sample-return mission on the books for future Mars exploration expeditions, but a bird in the hand….
The scientific debate over these rocks has less to do with the bigger question of life on Mars, and more to do with whether the features studied in these specific samples are evidence of it. Neither possibility—whether the features are biological or non-biological in origin—has been ruled out by the evidence, yet. How much a return sample mission to Mars targeting a chosen geological location, rather than meteorite samples blasted from who knows where, might tell us?
And how cool would it be to step off a spaceship onto Mars and set forth on a trek with a rock hammer and microscope? Field prospecting conducted by future humans exploring Mars won't be quite that simplistic of course, but can you imagine being there in person, digging into a Martian rock with your pick and peering through a magnifier to see what's there—what may have been left there, long ago, like a message whispered to you across time, through the living rock?