As seasons come and go on Mars, NASA's Curiosity rover has been
diligently sniffing and digging away, looking for signs the planet could
have supported life.
The latest data shows huge swings in the level of methane in the atmosphere as the seasons change, and new types of organic molecules capable of preserving life just beneath its surface.
The discoveries, reported today in two papers in the journal Science, while not evidence of life, provide more tantalising clues about what's happening on Mars, for future missions to investigate.
Spikes and plumes of methane in Mars's thin atmosphere have been detected by several missions over more than a decade, but they have been frustrating to study, said Christopher Webster, who led the methane study.
"These spikes and plumes … they never come back," he said.
On Earth, methane is mainly produced by biological processes. But the origin of methane on Mars has long been debated.
While it could be produced by microorganisms under the surface of Mars, it could also be produced by non-biological processes such as chemical reactions in rocks, or the breakdown of organic matter in dust delivered by comets or meteors, by UV radiation.
Since it landed at the Gale Crater in 2012, the Curiosity rover has been sniffing out methane in the area. Over time, a picture of the ebb and flow of methane on Mars has emerged.
"For the first time we have something that we can get a handle on," said Dr Webster of NASA's Jet Propulsion Laboratory.
Three Mars years' worth of data shows that along with spikes in methane, levels swing between 0.24 and 0.65 parts per billion, peaking in the northern hemisphere summer.
"You're seeing a factor of three change in the methane in the atmosphere of Mars. That's a big change," Dr Webster said.
Dr Webster said the difference was much larger than what
you would expect if the methane was produced by the breakdown of organic
matter from space.
"We've been able to rule out some of the more simple or accepted ideas of Mars's methane," Dr Webster said.
"The only thing that fits the data is that you have a source of methane below the surface.
"We cannot rule out its creation from biological activity … [But] it could also be rock chemistry."
Dr Webster said the data pointed to methane trapped in water-based crystals deep under the planet's surface, which slowly seep to the surface when temperatures rise.
"As temperatures change from winter to summer, the methane changes greatly because as the surface gets a little bit warmer it releases a lot more methane," he said.
In 2013, it confirmed organic compounds in rocks in a deep part of the crater called Yellowknife Bay, said Jennifer Eigenbrode, who led the organic molecule study published in Science.
But the deposits were much smaller than they had anticipated.
"A lot of us were left scratching our heads trying to figure out, 'What does this mean?' Then we turned around and realised, 'Let's just go and find more'," said Dr Eigenbrode of NASA's Goddard Space Flight Centre.
They hit pay dirt about 6.5 kilometres away, at two sites near Pahrump Hills at the base of Mt Sharp.
Thimble-sized samples of material baked slowly in temperatures of between 500–840 degrees Celsius, revealed the grey mudstone contained different carbon-based molecules to those found at Yellowknife Bay.
These molecules appeared to come from a much larger molecule, and contained high levels of sulfur.
"Those two features are very important for the preservation of organic material in rock on Earth," Dr Eigenbrode said.
Although there is not enough information to know whether the carbon molecules were created by biological or non-biological processes, it is possible that they could be a source of methane, Dr Eigenbrode said.
"They could be changed from something like we've observed at the base of the mountain into methane that eventually makes its way back in to the atmosphere," she said.
"Ideally we want to get to samples that have not been irradiated. To do that you either have to find an outcrop at the surface that has been recently exposed … or you have to drill deep," she said.
While the Curiosity rover only scrapes off the top 5 centimetres, ExoMars's MOMA lab which is planned to be launched in 2020 will go down 2 metres.
Dr Webster is also awaiting results from the current ExoMars Trace Gas Orbiter (TGO) mission, which is orbiting the Red Planet, sniffing methane.
Even though the TGO mission can't get as close to the source as the Curiosity rover, Dr Webster said it could locate potential areas where methane is concentrated or coming from.
"That would be exciting because if that is done within two years, NASA can send a mission specifically to that place," he said.
The latest data shows huge swings in the level of methane in the atmosphere as the seasons change, and new types of organic molecules capable of preserving life just beneath its surface.
The discoveries, reported today in two papers in the journal Science, while not evidence of life, provide more tantalising clues about what's happening on Mars, for future missions to investigate.
Spikes and plumes of methane in Mars's thin atmosphere have been detected by several missions over more than a decade, but they have been frustrating to study, said Christopher Webster, who led the methane study.
"These spikes and plumes … they never come back," he said.
On Earth, methane is mainly produced by biological processes. But the origin of methane on Mars has long been debated.
While it could be produced by microorganisms under the surface of Mars, it could also be produced by non-biological processes such as chemical reactions in rocks, or the breakdown of organic matter in dust delivered by comets or meteors, by UV radiation.
Since it landed at the Gale Crater in 2012, the Curiosity rover has been sniffing out methane in the area. Over time, a picture of the ebb and flow of methane on Mars has emerged.
"For the first time we have something that we can get a handle on," said Dr Webster of NASA's Jet Propulsion Laboratory.
Three Mars years' worth of data shows that along with spikes in methane, levels swing between 0.24 and 0.65 parts per billion, peaking in the northern hemisphere summer.
"You're seeing a factor of three change in the methane in the atmosphere of Mars. That's a big change," Dr Webster said.
"We've been able to rule out some of the more simple or accepted ideas of Mars's methane," Dr Webster said.
"The only thing that fits the data is that you have a source of methane below the surface.
"We cannot rule out its creation from biological activity … [But] it could also be rock chemistry."
Dr Webster said the data pointed to methane trapped in water-based crystals deep under the planet's surface, which slowly seep to the surface when temperatures rise.
"As temperatures change from winter to summer, the methane changes greatly because as the surface gets a little bit warmer it releases a lot more methane," he said.
Curiosity hits pay dirt at Mt Sharp
NASA's rover hasn't just been sniffing the air as it's trundled across the Gale Crater — it has also been drilling just below the surface of the 3.5 billion-year-old lakebed in search of organic molecules.In 2013, it confirmed organic compounds in rocks in a deep part of the crater called Yellowknife Bay, said Jennifer Eigenbrode, who led the organic molecule study published in Science.
But the deposits were much smaller than they had anticipated.
"A lot of us were left scratching our heads trying to figure out, 'What does this mean?' Then we turned around and realised, 'Let's just go and find more'," said Dr Eigenbrode of NASA's Goddard Space Flight Centre.
They hit pay dirt about 6.5 kilometres away, at two sites near Pahrump Hills at the base of Mt Sharp.
Thimble-sized samples of material baked slowly in temperatures of between 500–840 degrees Celsius, revealed the grey mudstone contained different carbon-based molecules to those found at Yellowknife Bay.
These molecules appeared to come from a much larger molecule, and contained high levels of sulfur.
"Those two features are very important for the preservation of organic material in rock on Earth," Dr Eigenbrode said.
Although there is not enough information to know whether the carbon molecules were created by biological or non-biological processes, it is possible that they could be a source of methane, Dr Eigenbrode said.
"They could be changed from something like we've observed at the base of the mountain into methane that eventually makes its way back in to the atmosphere," she said.
Future missions to dig deeper
Dr Eigenbrode hopes further details about the nature of the carbon molecules will emerge with future missions, such as the European Space Agencies ExoMars Mission or NASA's Mars 2020 mission."Ideally we want to get to samples that have not been irradiated. To do that you either have to find an outcrop at the surface that has been recently exposed … or you have to drill deep," she said.
While the Curiosity rover only scrapes off the top 5 centimetres, ExoMars's MOMA lab which is planned to be launched in 2020 will go down 2 metres.
Dr Webster is also awaiting results from the current ExoMars Trace Gas Orbiter (TGO) mission, which is orbiting the Red Planet, sniffing methane.
Even though the TGO mission can't get as close to the source as the Curiosity rover, Dr Webster said it could locate potential areas where methane is concentrated or coming from.
"That would be exciting because if that is done within two years, NASA can send a mission specifically to that place," he said.
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