NASA's Curiosity rover has made a new discovery of momentary methane spikes in the Martian atmosphere that could be the first evidence of life on the planet. The methane spikes could have come from microbial organisms on Mars.
Curiosity rover discovered a momentary spike in methane levels at its Gale Crater landing area. The rover detected the spike through analysis of gas samples by its Tunable Laser Spectrometer (TLS), which uses "intense light" to conduct analysis.
While taking four measurements over a period of 60 Martian days (sols), Curiosity detected a ten-fold increase in methane levels that dissipated quickly.
Scientists are trying to explain the cause of the fluctuation.
The methane spike is of special interest to scientists because here on planet Earth, methane is closely associated with living organisms, including microbes, which produce the gas in large quantities. Most of the methane in the Earth's atmosphere is produced by living organisms.
According to Paul Mahaffy, a scientist at NASA's Goddard Space Flight Center and one of the authors of the new study published online on Dec. 16, 2014 in the journal Science, although detection of significant amounts of methane could be indicative of the presence of microbial life, the mere fact does not prove the existence of life on Mars because there are other physical and geological processes that could generate methane gas in the Martian atmosphere.
"Right now, it's too much of a single-point measurement for us really to jump to any conclusions. So all we can really do is lay out the possibilities. And we certainly should have an open mind. Maybe there are microbes on Mars cranking out methane, but we sure can't say that with any certainty. It's just speculation at this point."Although this is not the first time that scientists have detected fluctuations in the levels of methane in the Martian atmosphere, the new data shows an unusual spike pattern that has never been detected.
Curiosity found that the background level of methane in the Martian atmosphere averages about 0.7 parts per billion, a level lower than scientists had expected, yet higher than the previous year's readings by Curiosity after it landed in the 96-mile wide (154km) Gale Crater region in August 2012 and began exploring the area.
Mars exploration expert Jan-Peter Muller told Space that Curiosity's readings last year dampened hopes about finding life on the Red Planet. Even the background level of 0.7 parts per billion later detected could have been generated by solar radiation breaking down organic material brought to the Martian surface by impacting space rocks.
The methane spike rose from the average background level of 0.7 parts per billion to about 7 parts per billion in about 60 Mars days. It was detected over a small area and disappeared rapidly over a short distance.
The first of the high measurements was detected in Nov. 2013, when Curiosity measured the gas at concentration levels of 5.5 parts per billion. The rover took a second measurement after two weeks and recorded 7 parts per billion. A third measurement taken soon after revealed the same level. A fourth measurement taken a few weeks later found 9 parts per billion. The final measurement, taken six weeks later, found that the level had fallen back to the average background level of about 0.7 parts per billion.
"The persistence of the high methane values over 60 sols (Martian days) and their sudden drop 47 sols later is not consistent with a well-mixed event, but rather with a local production or venting that, once terminated, disperses quickly."Explaining away the spike has proved difficult. It could not have been due to a comet or asteroid impacting on the surface of the planet because a space object that could explain Curiosity's readings would have to be a large rock that leaves an easily detectable crater as evidence.
The scientists also noted that the short duration of the methane spike was not consistent with the suggestion that it was released from ice-trapped volcanic deposits called Clathrates; nor could it have been derived from methane previously locked in the soil.
Despite having ruled out a long list of other possible sources of the spike, the scientists remained cautious about jumping to far-reaching conclusions but acknowledged that "methanogenesis," production of methane by microbial organisms or "methanogens," is one of the possible explanations of the observation.
"Our measurements spanning a full Mars year indicate that trace quantities of methane are being generated on Mars by more than one mechanism or a combination of proposed mechanisms -- including methanogenesis either today or released from past reservoirs, or both."According to Christopher Webster at NASA's Jet Propulsion Laboratory in Pasadena, California, and lead author of the new study, scientists have suggested that the methane spike could have been caused by gas trapped below ground released to the surface somewhere near Curiosity's location.
"Because of the way it [the methane] behaves, we believe it's a smaller, closer source [rather] than it is a bigger, further away source. But as far as the source of that methane, we cannot rule out biological activity, whether it's today or in the past, and we cannot rule out geophysical activity."While scientists would have loved to be able to trace the source of the methane gas spike, believed from evidence of wind direction to be north of the rover, and to determine the relative types (isotopes) of methane released, Curiosity is not equipped for the task, according to Webster. Scientists will have to wait for ESA's ExoMars mission, which will land a better equipped rover on the planet in 2019.
Information about the type of methane released would help scientists determine whether it came from biological sources or physical geological processes not linked with life processes.