By Marc Kaufman
Washington Post Staff Writer
Friday, January 16, 2009
Something is happening beneath the surface of Mars that causes substantial amounts of methane gas to vent regularly into the atmosphere, a discovery that NASA scientists said yesterday represents the strongest indication so far that life may exist, or once existed, on the planet.
The methane is released into the atmosphere in specific areas and at regular times, they found, in a pattern that would be consistent with the gas being a byproduct of biological activity beneath the planet's parched surface.
Principal investigator Michael Mumma, of NASA's Goddard Space Flight Center, said the detection does not mean that life definitely exists on Mars, since the gas can also be produced by subsurface geological or chemical processes.
Nevertheless, "we believe this definitely increases the prospects for finding life on Mars," said Mumma, whose findings are being published today in the journal Science. "No other discovery has done as much to increase the chances of finding life."
The scientists detected the plumes of methane during two Martian summers, when the planet's large formations of subsurface ice may melt and release the gas.
Most of the methane in Earth's atmosphere is produced by bacteria in creatures large and small. Even if turns out that the Martian methane is from non-biological processes -- a far less dramatic prospect -- that would nonetheless reshape thinking about the planet, which scientists thought to be geologically dead and chemically unlikely to produce much of the gas.
Scientists have been working to confirm the presence of methane on Mars since it was tentatively detected in 2003, first by Mumma and then by scientists working with the European Space Agency. The new report confirms that discovery, describing intense, recurring but relatively brief gas releases that are consistent with either biological or active geological origins.
The new data were gleaned by NASA's Infrared Telescope Facility atop Mauna Kea, Hawaii, and a telescope in Chile. The earlier reports of methane came from Mars Express, the European Space Agency's orbiting satellite. Scientists used instruments called spectrometers to detect the "fingerprints" of methane molecules by the way they absorb sunlight.
Mumma said the methane does not last long in the Martian atmosphere, which is made up largely of carbon dioxide that breaks down the gas much more quickly than on Earth. That means, he said, that the methane detected was almost certainly released recently from underground reservoirs, although it could have been stored there for a long time.
The plumes were detected above a handful of Martian hot spots hundreds of miles apart, including Nili Fossae, Syrtis Major and Arabia Terra. Previous research has shown that liquid water once covered some of that area and detected mineral deposits that require standing water in order to form. Images taken by a Mars orbiter in 2005 also suggest that water, or liquids of some kind, might still flow at times on the surface.
Michael Meyer, head of NASA's Mars program, said at a news conference that the report would spark intense debate and probably criticism in the field. He called the science important and sound but said it would take time to see whether it would change scientists' understanding of Mars.
The methane discovery comes as researchers on Earth are finding previously unknown colonies of "extremophiles" living far below the surface and in conditions that were long considered to be uninhabitable. One of the experts at the news conference was Lisa Pratt of Indiana University, who was part of a team that identified a microbe two miles down in a South African gold mine that lives entirely without drawing energy from sunlight, a process called photosynthesis. The microbe's energy source is the radioactive decay of nearby rocks, a process known as radiolysis.
In today's paper, Mumma's team pointed to the South Africa findings, saying that it might be possible for similar life forms "to survive for eons" below Mars' subsurface ice, "where water is again liquid, radiolysis can supply energy, and CO2 can provide carbon. Gases accumulated in such zones might be released to the atmosphere if pores or fissures open seasonally, connecting these deep zones to the atmosphere at scarps, crater walls, or canyons."
Pratt called the methane find "a breathtaking discovery." She noted that on Earth, methane is not only a waste product of some microbes but also a potential nutrient for specialized organisms.
"So much attention has been given recently to looking for evidence of past life on Mars, and now it appears that we need to seriously consider the possibility of a present-day subsurface Martian ecosystem," Pratt said. "Mars just got a whole lot more interesting."
Mumma, a senior investigator with Goddard's Center for Astrobiology and its Solar System Exploration Division, has been looking for methane on Mars since the late 1980s. The gas was difficult to detect because it is relatively scarce and breaks down quickly, and some earlier reports of detections have been controversial. But Mumma said the methane signature in his new data is "very strong indeed," and the fact that it occurs only locally and at specific times is also well documented.
Because venting methane was found at several locations, Mumma has been urging NASA to consider them as landing sites for the Mars Science Laboratory, a $2 billion rover scheduled to launch in 2011. He said some of the terrain would be difficult for a landing, but he said he hopes the methane discovery will focus attention on how NASA might further explore its origins.
"Suppose we put a probe into a fissure at one of the release sites site and we could get measurements from some extant life form," he said. "We could then sequence the life form and see if it had the same origins as Earth life. What could be more compelling?"
The most common non-biological way that methane gets into the Earth's atmosphere is volcanic eruptions that spew it out along with rock, magma and a great deal of heat. Sulfur dioxide accompanies volcanic eruptions on Earth, but scientists have not found much of that compound in the Martian atmosphere -- leading them to conclude that the planet is no longer volcanically active. As a result, they do not consider volcanoes to be the source of that planet's methane.
Methane can also be created by the interaction of water and subsurface minerals such as olivine in the presence of heat. This process, call serpentization, is known to occur beneath Earth's surface.
Methane is also known to be much more broadly present on Titan, one of Saturn's moons and another target for scientists looking for life beyond Earth.