Planets

Did Mars' Methane Come from Comets?

A correlation is found between when methane plumes appear on Mars and when the planet passes through remnants of a comet.

One of the most provocative questions about Mars today is what is causing periodic spikes in the amount of methane in the planet's atmosphere.

On Earth, methane is strongly tied to biological activities, raising the prospect that colonies of methane-emitting microbes might be living on Mars. Another option is that the gas stems from geological activities, though so far attempts to match the methane spikes with the seasons have not panned out.

NASA scientist Marc Fries and colleagues have another idea – meteor showers.

Curiosity Detects Mysterious Methane Spikes on Mars

Fries, who studies meteorites, comet samples other extraterrestrial materials, says there is a correlation between when the methane plumes appear and Mars' transit through a region of space littered by remnants of a comet, the source material for meteor showers.

"Carbonaceous solids such as those of cometary origin can generate a significant volume of methane ... under UV (ultraviolet) radiation," Fries and colleagues wrote in a paper presented Monday at the Lunar and Planetary Science Conference in The Woodlands, Texas.

The scientists found that all known methane detections occurred within 16 days of Mars' orbit encountering the orbit of a comet capable of producing a meteor shower.

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"You have a mechanism that produces methane and a time correlation between the occurrence of meteor showers and the appearance of methane," Fries told Discovery News.

Not everyone is convinced. NASA planetary scientist Michael Mumma, who led a team that made the initial findings of methane spikes on Mars, said there have been many more times when Mars approached known meteor streams and methane was not detected.

"Our team searched (for methane) on more than 30 multi-day campaigns since 2002, and detected methane on only three (Jan 2003, March 2003 and May 2005)," Mumma wrote in an email to Discovery News.

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"Other teams report similar rare detections. In short, no systematic correlation with meteor streams," he said.

Fries points out ground-based telescopes have to account for methane in Earth's atmosphere, and that NASA's Mars rover Curiosity, which has chemical sniffers to hunt for the gas, has a very local sampling field. Also, not all comet streams end up triggering meteor showers.

The final word may come from Europe's Trace Gas Orbiter, which was launched last week for a seven-month journey to Mars. Once it puts itself into orbit, the spacecraft will need about another year to properly position itself for observations.

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"We can basically test this hypothesis of whether or not the methane plumes are coming from meteor showers," Fries said.

"We know when the meteor showers are supposed to happen ... and we can measure and see if there's a significant amount of material dropped onto Mars. Then we can turn around and watch for methane."

NASA's Spirit rover on Mars spotted these "shooting stars," or meteors in the Martian night sky.

NASA's rover Curiosity has begun drilling operations for the third time on Mars. Currently located at a geologically interesting location nicknamed "The Kimberley," the one-ton rover also took the opportunity to photograph itself and the surrounding landscape in some stunning Martian "selfies." In this scene, Curiosity appears to be leaning its "head" -- a suite of instruments including the Chemcam (the laser "eye") and Mastcam cameras -- to the side, capturing the 5 kilometer-high Aeolis Mons (a.k.a. "Mount Sharp") on the horizon. The self portrait has been stitched together

by Discovery News' Jason Major

from a series of raw photographs (taken on sol 613, April 28, of the mission) by Curiosity's robotic arm-mounted Mars Hand Lens Imager (MAHLI) instrument.

In this scene, Curiosity appears to be concentrating hard on a rock of interest -- dubbed "Windjana" by mission scientists after a gorge in Western Australia -- that it has cleaned with its robotic arm-mounted Dust Abrasion Tool. A grey circular patch can be seen on the otherwise rusty rock's surface where the tool has scrubbed away any surface dust ready for analysis and drilling. This beautiful selfie was created

by JPL's Doug Ellison

, after assembling a collection of photos from the rover's Mars Hand Lens Imager (MAHLI) on sol 613 (April 28) of the mission. Curiosity's selfies not only produce some breathtaking scenes, they are also used by mission engineers to keep tabs on the condition of the rover the more time it is exposed to the harsh Martian environment.

Curiosity used its Mastcam to photograph this closeup of its Rock Abrasion Tool. The instrument spins the wire-bristle brush over rock surfaces to remove layers of dust that has accumulated.

After brushing, a grey circle of rock beneath the ruddy Mars dust is exposed for further analysis. In this photo by Curiosity's Mars Hand Lens Imager (MAHLI), the texture of Mars dust is obvious and fine cracks or seams in "Windjana" can be seen. "In the brushed spot, we can see that the rock is fine-grained, its true color is much grayer than the surface dust, and some portions of the rock are harder than others, creating the interesting bumpy textures,"

said Melissa Rice

, Curiosity science team member, of the California Institute of Technology, Pasadena. "All of these traits reinforce our interest in drilling here in order understand the chemistry of the fluids that bound these grains together to form the rock."

On April 29, Curiosity used its drill to bore a 2 centimeter hole into Windjana. This is only the third rock Curiosity has drilled into since landing on the red planet on Aug. 5, 2012. The grey color obviously extends deeper into the rock than just on its surface, and the powder created can provide a pristine rock sample for further analysis, helping mission scientists understand how the rock formed and under what environmental conditions.

The first two drilled rocks were located in Yellowknife Bay, approximately 4 kilometers from The Kimberley. Those rocks were determined to be mudstone slabs formed through water action and sediment, providing compelling evidence that the interior of Gale Crater used to play host to a lakebed and may have provided a habitable environment for ancient microbial life. This new drilling operation will provide more clues as to how rock formed in the region, revealing more tantalizing clues as to the past habitability of the red planet.