Two teams of ground-based observers presented data that support their previous tentative discovery of methane on Mars.
Michael Mumma of Goddard Spaceflight Center (and PI of the Goddard NAI team) reported spectroscopic measurements made with two different telescopes. Observing with both the NASA IRTF in Hawaii and the Gemini South telescope in Chile, Mumma's team detected two different spectral lines of methane. (In a search for trace amounts of a gas, two spectral lines are much better than one for eliminating possible misidentifications). The average quantities of methane agreed with previous reports, but in addition Mumma now has spatial resolution. The distribution of methane is not uniform but is concentrated in certain areas, suggesting localized sources for release of the gas. Measured concentrations are as high as 250ppm (parts per million).
Vladimir Krasnopolsky of the Catholic University of America observed with a different kind of spectrograph on the Canada-France-Hawaii telescope, also in Hawaii. Based on several spectral lines, his team estimate an average methane abundance in the martian atmosphere of 10ppm, but they also see enhancements at specific locations, not inconsistent with Mumma’s results.
There are also spacecraft data from the European Mars Express mission, in orbit about Mars. In September 21 press release, the Mars Express team reported the detection of methane and suggested that methane and water vapor abundances were correlated – as if both water vapor and methane were being released together from subsurface reservoirs.
These results are exciting to astrobiologists because of the short lifetime of methane in the atmosphere. After about 300 years, the methane is chemically dissociated by sunlight. Therefore the source of methane is either some very recent event, such as the impact of a small comet, or else it probably represents a continuous outgassing, with new methane replacing the losses. The spotty distribution of the methane suggests outgassing from the subsurface. Whether the sources are volcanic, or vaporizing permafrost deposits of water and methane ice, or are possibly biological in nature remains to be seen.
Methane from the Earth’s interior is also the subject of a recent report from scientists led by Henry Scott of the Carnegie Institution NAI team. Their high-pressure lab experiments and supporting theoretical calculations show that methane can form and be stable at considerable depth below a planet’s crust. This result suggests a new non-biological source for methane in planetary interiors, which could be relevant for both terrestrial and martian sources of atmospheric methane.
Meanwhile, back on Mars the two active NASA rovers are waking up after surviving the cold martian winter. Steven Squyres, the PI for the rovers, and other members of his team, summarized recent activity at the DPS meeting. The Opportunity rover is still in Endurance Crater in the Meridiani Plains, where it is maneuvering to approach some of the steeper exposed faces of sedimentary rock. Spirit is high in the Columbia Hills within the large Gusev Crater, and it may undertake to climb even higher. Both rovers are expected to operate for at least another 6 months on Mars, barring unforeseen accidents or failures.