Last week, NASA’s Curiosity rover discovered high amounts of methane in the air on Mars, leading to excitement whether this was an indication of life on the Red Planet, or beneath its surface. But on Monday, NASA reported that the methane had fallen back to usual levels. The setback means the question of life remains unanswered. What were scientists hoping to find, and what does methane signify?
What is methane?
On Earth, methane (CH4) is a naturally occurring gas. Most of the methane on Earth is produced in biological processes — some of it by microbes, and some occurring as underground natural gas that hd been formed by earlier generations of microbial life. Many of these methane-producing microbes live in the digestive systems of animals, especially cows.
However, methane can also be produced by abiotic processes (those that do not involve living organisms). It has been found to occur in formations such as rocks, springs and aquifers, and studies have concluded that it was formed there by chemical reactions between carbon and hydrogen atoms at low temperature.
Once it is released into the atmospheres of either Earth or Mars, methane is relatively short-lived. Since the time the gas was first detected on Mars, it has been considered a potential biomarker. The first time was in 2003 by the Mars Express, a European Space Agency orbiter. Since then, there has been further evidence of the gas in Mars’ atmosphere.
So what’s new?
In most previous observations, the concentration of methane in the Martian air has been low. Then in 2013, Curiosity — which had landed on Mars in 2012 — detected methane in a concentration of seven parts per billion by volume. Now, methane concentrations on Earth are much higher — the global mean is over 1,800 parts per million — but the Mars measurement caused excitement because it was much higher than previous readings. This concentration continued for about a couple of months, then ebbed away before scientists could establish where the methane came from.
Last week’s readings were an unprecedented 21 parts per billion. On Earth, it created excitement to the extent that scientists at NASA’s Jet Propulsion Laboratory cancelled Curiosity’s original schedule for the weekend, so that it could repeat the experiment. They were hoping to detect the source of the gas, and in the process clues that might point to the existence of life on the Red Planet.
On Wednesday, NASA reported that the second reading had fallen back to less than 1 part per billion..This suggests that last week’s methane detection was a transient methane plume, which has been observed in the past, NASA explained on its website. While scientists have observed the background levels rise and fall seasonally, they haven’t found a pattern in the occurrence of these transient plumes.
Curiosity doesn’t have instruments that can definitively say whether the source of the methane is biological or geological. “With our current measurements, we have no way of telling if the methane source is biology or geology, or even ancient or modern,” the NASA website quoted Sample Analysis at Mars (SAM) Principal Investigator Paul Mahaffy of NASA’s Goddard Spaceflight Center as saying.
To determine where the plumes are located on Mars, scientists would need a clearer understanding of these plumes, combined with coordinated measurements from other missions, NASA said.
“The methane mystery continues. We’re more motivated than ever to keep measuring and put our brains together to figure out how methane behaves in the Martian atmosphere,” NASA quoted Ashwin Vasavada, Curiosity’s project scientist at the Jet Propulsion Laboratory, as saying.