New hints of life on Mars
Odd spikes in methane on the planet are raising suspicions
STRANGELY HIGH SPIKES in levels of methane in the Martian atmosphere have been measured by NASA’s Curiosity rover. Some scientists have speculated that this might be a sign of current life on the planet, as microbes on Earth release methane as part of their digestion process. But there are several other possible reasons for the gas changes.
“This temporary increase in methane – sharply up and then back down – tells us there must be some relatively localised source,” says mission scientist Sushil Atreya from the University of Michigan in Ann Arbor. “There are many possible sources, biological or non-biological, such as interaction of water and rock.”
In late 2013 and early 2014, four measurements of methane by Curiosity averaged seven parts per billion. Before and after that, readings averaged only a tenth of that level. The reason for the sudden increase is not known, but organic molecules containing carbon, and usually hydrogen, are the chemical building blocks of life.
“We will keep working on the puzzles these findings present,” says John Grotzinger, a Curiosity rover scientist from the California Institute of Technology. “Can we learn more about the active chemistry causing such fluctuations in the amount of methane in the atmosphere? Can we choose rock targets where identifiable organics have been preserved?”
Apart from microbes, another possible source of the methane are clathrates, ice in which methane gas is trapped. Some kind of trigger could destabilise the clathrates, allowing methane to seep up through fissures in Martian rocks and enter the atmosphere.
In other experiments, Curiosity has found organic chemicals in powder drilled from a rock dubbed ‘Cumberland’. These could have formed on Mars or been delivered by meteorites. Although Curiosity’s intriguing discoveries don’t say anything definitive about whether Mars has ever harboured life, they highlight vigorous chemical activity on the planet and suggest life isn’t out of the question.
“This first confirmation of organic carbon in a rock on Mars holds much promise,” says Curiosity scientist Roger Summons from the Massachusetts Institute of Technology. He hopes the rover will find further rocks on Mars that have different and even more diverse organic compounds. www.nasa.gov/msl