Curiosity Confirms Organics On Mars

The National Aeronautics & Space Administration’s Mars rover Curiosity has discovered that organic compounds are present in the soil of Mars. Additionally, Curiosity recently detected a local but dramatic surge of methane of unknown origin in the martian atmosphere (Science 2014, DOI: 10.1126/science.1261713).

Although organics, particularly methane, can be produced by living organisms, these compounds can also be synthesized by abiotic reactions of soil, water, and solar radiation. And right now, scientists say they have no way of determining their source.

Still, the discoveries have generated great excitement among Mars scientists.

“We now have full confidence there is methane and organics in ancient rocks,” Curiosity project scientist John P. Grotzinger said at a Dec. 16 press conference at the American Geophysical Union (AGU) meeting in San Francisco.

Organic molecules are not in and of themselves definitive proof that life once existed, or does exist, on Mars, Grotzinger said, “but it is the kind of material you would look for if life ever originated on Mars.”

At last year’s AGU meeting, Curiosity scientists tentatively announced that the rover had detected two organics, chlorobenzene and dichloropropane, during the processing of soil samples. However, at the time, they couldn’t be sure whether these molecules were derived from Mars or from inside Curiosity’s instruments.

Now, after a year of rigorous testing, they’re sure. The chlorobenzene levels detected in the processed samples are much higher than could be produced from the instruments alone.

Along with the aforementioned compounds, the scientists also confirmed the presence of dichloroethane and dichlorobutane. They think the molecules are likely the products of precursor organics from the martian soil and were formed during the heating of the perchlorate-rich soil.

A paper about the organics is under review at the Journal of Geophysical Research-Planets.

Methane plumes have been detected on Mars a number of times, but the new measurements are the first from a craft on martian ground. Over a period of 20 months, Curiosity’s laser spectrometer recorded background atmospheric levels of methane of about 0.7 ppb. But then suddenly methane levels spiked more than 10-fold. “It was an ‘oh my gosh’ moment,” Curiosity scientist Christopher R. Webster said at the conference. The methane levels climbed to 9 ppb over a period of several months.

“Six weeks later, we looked again and it had completely disappeared,” Webster said.

Scientists don’t know the origin of the methane, but suggest it is periodically escaping from clathrates under the soil surface.

If future soil samples show large enough amounts of any of these compounds, scientists might be able to look for carbon isotopes such as ¹³C. Lower ¹³C levels relative to ¹²C would strongly suggest the organics have a biological origin.