There are no cows on Mars.
Of that, planetary scientists are certain, which leaves them puzzling over what could be producing methane gas detected in the thin Martian air. Methane molecules are easily blown apart by ultraviolet light from the Sun, so any methane around must have been released recently.
Could the gas be burbling from something alive? Cows, after all, burp methane on Earth. Other creatures, including a class of micro-organisms that live without oxygen, also produce methane.
Launch and 2012 landing
The National Aeronautics and Space Administration (NASA) could get some answers soon. On the launching pad at Cape Canaveral in Florida is a spacecraft, the Mars Science Laboratory, that is scheduled to lift off on Friday/Saturday and reach Mars next August. It will deliver an S.U.V.-size rover named “Curiosity” that carries an instrument that can detect methane in the air, and if it does, it will unleash new excitement about the prospect of life on Mars.
“Based on evidence, what we do have is, unequivocally, the conditions for the emergence of life were present on Mars — period, end of story,” said Michael J. Mumma, a senior scientist for NASA at the Goddard Space Flight Center in Greenbelt, Md., who led one of three teams that have made still-controversial claims of detecting methane in Mars's atmosphere. “So life certainly could have arisen there.”
Because Mars is smaller than Earth, it cooled faster, and it probably would have been hospitable for life earlier. That raises the intriguing possibility that pieces of Mars containing microbes were blasted into space by asteroid impacts and later landed on Earth, seeding life here.
In other words: we could all be descendants of Martians.
The possibility of Martians has long fuelled the imagination of Earthlings, from the Edgar Rice Burroughs Barsoom novels to the canals Percival Lowell deluded himself into seeing through his telescope to “War of the Worlds.”
Other times, the pendulum swung back the other way. Mariner 4, the first space probe to whiz past Mars, in 1965, sent back pictures not of verdant forests, but of barren rocks. And NASA's two Viking landers in 1976, equipped with sophisticated life chemistry experiments, analysed the soil and found it devoid of the organic building blocks of life.
Mars, it appeared in 1976, was really most sincerely dead. “Things looked so grim for exobiology on Mars,” said Christopher F. Chyba, a professor of astrophysical sciences at Princeton University. “We made this tremendous investment in two Viking landers. There was a backlash of the people who felt the biology was oversold and premature.”
Geology and climate
NASA subsequently played down the notion of life on Mars and instead set out on a methodical campaign to explore the past geology and climate of Mars. Although Mars today looks dry and cold — dead — geological markings like gullies, dry lake beds and colossal canyons point to a liquid past. “Follow the water” became the mantra. NASA's last two rovers, “Spirit” and “Opportunity,” found convincing evidence of environments that were habitable in the distant past. “Curiosity” will go further, looking for carbon-based molecules, including methane, that are the building blocks of life.
Recent orbital images show that water might still occasionally flow on the surface of Mars. New knowledge about life on Earth and how it can thrive in seemingly hostile environments, like the dark, boiling waters near ocean-bottom volcanic vents, also made scientists less dismissive of the notion that life persists on Mars. In 1996, a team of NASA scientists announced that they had found fossilised microbes in a Martian meteorite that had landed in Antarctica. Those claims remain at least as controversial as the methane findings.
But short of photographing a cow or some other life form ambling among the rocks, “Curiosity” is not going to discover life. There are two lander missions that are to follow “Curiosity” — collaborations between NASA and the European Space Agency. Christopher E. Carr, a research scientist at the Massachusetts Institute of Technology who is intrigued by the possibility that life on Earth could have started on Mars, has proposed an even more ambitious experiment: send a DNA sequencer to Mars. That, too, has yet to find a mission to fly on. Definitive answers may have to wait until a mission that brings Mars rocks back for study.
But that may be a very long wait. The Obama administration, mindful of tight federal budgets, has yet to give the green light on the lander missions, scheduled for 2016 and 2018, and is considering cancelling them. “Curiosity” may be the last spacecraft landing on Mars for many years. “That would derail the whole search for life, either extinct or extant, on Mars,” Dr. Mumma said. “That would be a disaster.”
—New York Times News Service