Methane Spikes on Mars Mystify Researchers

Transitory methane spikes recorded by NASA’s Curiosity rover on Mars in the atmosphere around it and the organics it found in the dust it drilled from a rock have perplexed the planetary scientists who appear wary of putting an identity tag on the phenomenon before further data help solve the puzzle.

Findings are based on atmospheric analyses done a dozen times in 20 months on the bed of an ancient lake in Gale crater with the SAM (Sample Analysis on Mars) laboratory suite of instruments aboard the rover. Results, published online in Science, show an average background methane abundance of around 0.7 parts per billion, which is considerably lower than that for interplanetary dust particles that rain on Mars, thus pointing to an indigenous source. Even more puzzling is the results of four separate measurements carried out during late 2013 and early 2014, which showed that the average figure jumped tenfold to 7.2 pp before dropping back to normal levels. Researchers interpret the results as showing the presence of an unknown source producing methane from time to time.

Methane is an organic molecule, containing carbon which is essential for life as we know it. But although they are building blocks of life, organics may exist without the presence of life. So the planetary scientists choose to tread cautiously concerning the putative source of methane, pointing out that besides microbial activity, it can also be produced through non-biological processes, like, for instance, reaction of chemicals in rocks with water.

Curiosity has also found various organics in the rock dust gathered from a mud rock named Cumberland it drilled on the lakebed in Gale crater. According to researchers, even though these not necessarily attest to microbial life on Mars anytime in its history, they show at least, in its distant past the planet had the right conditions for supporting life. Surveys done so far with orbiters and rovers have shown that Mars, 4.6 billion years old like the Earth and currently a dry and frigid world, was once balmy enough to allow the existence of seas and lakes on its surface. Deep canyons and gullies, sedimentary rocks on flat patches and the minerals they contain also show that surface had been shaped by water. Mars soil was recently found to be rich in frozen water. 

The data dug out by Curiosity from Cumberland rock made of sediments deposited on the lakebed in Gale crater, also shed light on hydrological history of Mars. Water molecules trapped in the lakebed minerals in the rock more than three billion years ago have revealed that Mars had lost most of its water before the formation of the lake and continued losing it thereafter.

Researchers have arrived at the conclusion by looking at the ratio of hydrogen isotopes to each other in the studied water molecules.

While the nucleus of the simplest version of hydrogen is composed merely of a single proton, that of a heavier version called deuterium contains a neutron in addition. Throughout the history of Mars, this ratio has changed. This is because the lighter hydrogen gets depleted by escaping into space from the atmosphere on which Mars cannot maintain a firm grip with its relatively small mass. Heavier deuterium thus increases its share in the atmosphere (and water).

The fact that the deuterium-hydrogen ratio Curiosity has found in the sample it collected from Cumberland which formed between 3.9 and 4.6 billion years ago is half the ratio in the present-day Mars atmosphere shows the planet had lost a considerable amount of its water after the rock had formed. The ratio in the samples, on the other hand, is three times of what was believed to be the rate in the water Mars had initially, which should be close to the rate measured for Earth’s oceans. This, in turn, shows that Mars had lost much of its water before the formation of the rock.