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Planetary News: Mars (2009)Are Methane Plumes Evidence of Life on the Red Planet?By Amir AlexanderJanuary 17, 2009
A group of scientists led by Michael Mumma of NASA's Goddard Space Flight Center have confirmed the presence of the gas methane in Mars's atmosphere. In an article published in the journal Science Express on January 15, 2009, Mumma and his colleagues describe how they used large telescopes on Earth to map out the methane concentration over nearly the entire surface of Mars. While scientists do not know the origin of the Martian methane, the authors note that on Earth methane is a strong indicator of the presence of life. With methane in the atmosphere of Mars now confirmed, "it would be prudent to start considering the possibility that microbial life may be present on Mars" said Lisa Pratt, Professor of Geological Sciences at Indiana University. The presence of methane on Mars did not come as a complete surprise. Back in 2003 the European orbiter Mars Express detected what appeared to be traces of methane in the Martian atmosphere, but the results were incomplete and some scientists considered them inconclusive. Meanwhile Mumma and his colleagues began their own systematic observations of Mars, intending to settle the methane mystery once and for all. Over the span of seven Earth years they observed the planet systematically, making use of NASA's Infrared Telescope Facility and the W.M. Keck Telescope, both at Mauna Kea, Hawaii. At each facility they utilized highly sensitive spectrometers to record the light spectrum reflected from the Red Planet. Since different gasses absorb different light frequencies (or "absorption lines"), analyzing the spectrum from Mars can tell scientists which gasses are present in the planet's atmosphere. Rather than observe the planet as a whole, Mumma and his team monitored it through a narrow slit that captured a single north-south band on the Martian surface. As the planet rotated, the band moved slowly over the entire surface of the planet, enabling the observers to measure for the presence at each location. By using this technique the article's authors were able not only to determine whether methane is present in general, but also to map out where it was present and in what concentration. With their map of methane distribution in the Martian atmosphere in hand, Mumma and his colleagues noted some intriguing patterns. First of all the presence of clear local concentrations of methane indicated that the gas was released into the atmosphere in the very recent past. This is because given sufficient time winds would distribute the gas evenly throughout the planet. Furthermore observations of the same location three (Earth) years apart at different seasons showed that a location rich in methane in the summer had far lower concentrations in the winter. This indicated that whatever methane was present in the atmosphere was quickly destroyed, and that a regular supply was necessary in order to maintain the gas in the atmosphere. It also suggested a seasonal pattern: methane was apparently released during the summer, and was largely gone by the middle of winter.
The most intriguing question to scientists, however, is the origin of all this methane. On our own planet there are two main sources of methane: one is geothermal vents, releasing gasses formed by geological processes deep underground; the other is methane-producing microbes, know as "methanogens." As of now, we know of neither geological activity nor biological activity on Mars, which appears to be a dead planet. But the presence of methane strongly suggests that at least one of these processes is, in fact, currently active. "Right now we do not have enough information to tell whether biology or geology – or both – is producing methane on Mars" said Mumma. "But it does tell us that the planet is alive – at least in the geological sense." The hypothesis that methane is being produced biologically on Mars is given some credence by the locations where the largest methane plumes were found. Terra Sabae, Nili Fossae, and Syrtis Major are all regions where scientists believe liquid water once flowed, and subterranean water may still be present. Is it possible that methanogenic microbes still survive in these regions, deep bellow the surface? Insulated by permafrost from the hostile surface, and nourished by liquid water, such microbes could produce methane that remained trapped underground for much of the year. During the summer, heat from the Sun would melt the ice and open frozen vents in the permafrost releasing a cloud of trapped methane into the atmosphere. Such a cycle would account for the seasonal variations noted noted by Mumma and his collaborators. This scenario, the authors point out, is not unknown on our own planet. In fact, they note, some organisms on Earth have survived isolated from the surface for millions of years. "On Earth microorganisms thrive about 1.2 to 1.9 miles beneath the Witwatersrand basin of South Africa" Mumma said. "It might be possible for similar organisms to survive for billions of years beneath the permafrost layer on Mars."
While the possibility that the methane concentrations point to the presence of life on Mars, or perhaps active geological processes, there are also more prosaic explanations for the gas plumes. For while it appears certain that the methane was only recently released into the atmosphere, this in itself does not prove that it was only recently produced. It is possible that the gas has been trapped deep beneath the planet's surface for billions of years, ever since the days when Mars was a geologically – and possibly biologically – active planet. Every summer when the Sun opens up frozen vents within the permafrost a small portion of the gas is released into the atmosphere, producing methane plumes. If this is the case, the Martian methane is not a sign of current life on the planet, but a relic from a distant time when Mars was a very different planet, far more similar to Earth. Are the methane concentrations observed by Mumma and his colleagues evidence that life is currently present on the Red Planet? We do not yet know. But the regions where plumes of methane were detected on Mars now beckon to us, calling us to resolve their mystery. The next time we send out a spacecraft to the Red Planet to search for life, we will know exactly where to look. Did you like this story? Send
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