In August, the Curiosity rover landed on Mars and began gathering data on the planet’s geology and atmosphere. While NASA has not yet released the Curiosity’s data, expected among its discoveries is a controversial substance: methane. While scientists agree that trace amounts of methane should be present, the concentrations of the gas consistently exceed predicted quantities, leaving researchers to wonder what has produced it.
On earth, methane is an extremely common organic compound. It is colorless and odorless but highly combustible, making it useful as fuel. Methane is the principal component of natural gas and is produced by living organisms as diverse as cattle, termites, and anaerobic bacteria.
It is not so easy to explain how Mars got its methane. Scientists say they expect to see some traces of the gas on Mars, but not the concentrations that consistently appear to be present. Telescopes first detected Mars’ methane, but many researchers dismissed those readings as interference from Earth’s atmosphere.
Recent evidence, however, emphasizes that the methane really is there. The Thermal Emission Spectrometer on the Mars Global Surveyor, an orbiting satellite that collected data from 1996 until 2006, detected relatively high levels of methane in Mars’ atmosphere. MGS revealed that Mars’ methane levels vary by location and season: they are highest in summer and autumn, in regions with volcanoes or other geothermal activity. Chris McKay, a Mars specialist at NASA, told SPACE.com, “Methane on Mars should have a lifetime of 300 years and should not be variable. If it is variable, this is very hard to explain with present theory. It requires unexpected sources and unexpected sinks.”
This makes it sound like the methane is produced by geology, not biology, but scientists are skeptical that geological processes can account for the quantity and variability of methane found. “Methane is really quite a rare gas in hydrothermal/volcanic exhalations,” Dirk Schulze-Makuch, an astrobiologist at Washington State University, said in an interview with SPACE.com.
While methane comprises less than 1% of Mars’ atmosphere, there is nonetheless a lot of methane in Mars’ air. Malynda Chizek, a graduate student in astronomy at New Mexico State University, uses a colorful image to describe to phys.org how much methane seems to be present. In order to produce the quantity of methane that MGS and other devices have observed, Chizek says that five million cows would have to generate 200,000 tons of methane per year.
Like many researchers, Chizek is eager to see what Curiosity will detect. The rover carries an advanced suite of chemical analysis equipment, the Sample Analysis at Mars (SAM). SAM can “sniff” gases in Mars’ air, and it can heat or chemically treat soil and rock samples to extract gases from them. SAM’s precision and diversity of tools will likely provide information that will help scientists identify the source of the methane.
Researchers are cautious when they hypothesize that the methane could be a clue toward life on Mars, but it is clear that many of them hope SAM will reveal that Mars once supported life. As Michael J. Mumma, a senior scientist at NASA’s Goddard Space Flight Center, told The Daily Galaxy, “Based on evidence, what we do have is, unequivocally, the conditions for the emergence of life were present on Mars — period, end of story.” The samples that SAM collects could reveal whether those conditions actually produced life, and perhaps hint at the nature of that life and why it disappeared. Mars’ mysterious methane might be all that remains of ancient (and probably microscopic) Martians.