Fleeting spikes of methane have been detected in the Martian
atmosphere several times over more than a decade, but none had been
independently confirmed — until now.
Using an instrument onboard the European Space Agency's Mars Express spacecraft, a team of scientists detected a methane spike on June 16, 2013 — backing up observations made a day before by NASA's Curiosity rover.
"A confirmation of measurements is the ultimate prize in planetary exploration," said Chris Webster, who is in charge of Curiosity's methane sensing instrument.
Even more importantly, the Mars Express team has been able to home in on a potential location of the methane spike 500 kilometres to the east of Gale Crater, they report in the journal Nature Geoscience.
A geological survey of the area, known as Aeolis Mensae, identified faults that extend below a region thought to contain shallow ice, said paper co-author Marco Giuranna of the National Institute of Astrophysics in Rome.
"Since permafrost is an excellent seal for methane, it is possible that the ice here could trap subsurface methane and release it episodically along the faults that break through this ice," Dr Giuranna said.
This sporadic belching process happens on Earth, where methane is mainly produced by microorganisms. But the origin of methane on Mars — and potential for life — has long been debated.
While microorganisms may be responsible, 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.
NASA's Curiosity arrived at the Gale Crater in 2012 and six months passed before any substantial methane was detected, said Dr Webster.
"Curiosity first reported less than 1.3 parts per billion upper limit in the first six months on Mars and we essentially said there's no methane on Mars," Dr Webster said.
That changed when the rover sniffed out two spikes: one around 5 parts per billion in June 2013, and another spike almost twice as big that lasted for two months between November 2013 and January 2014.
It has since detected continual low background levels that peak in the summer months.
But the findings split the science community, with some suggesting that the source of methane may have been Curiosity itself.
"There's no evidence of that whatsoever," Dr Webster said.
Then, late last year, scientists working on the latest spacecraft to sniff out methane on Mars — ExoMars Trace Gas Orbiter (TGO) — reported they'd found no gas in the red planet's atmosphere since observations from the ESA craft began in April last year.
The missing methane had scientists scratching their head.
Instead of pointing the instrument, known as the Planetary Fourier Spectrometer (PFS), above the surface and averaging emissions over the entire planet, it locked on to a feature in the landscape and tracked it.
This meant it could pick up local increases in methane.
The instrument detected a spike of 15.2 parts per billion, give or take 2.5 parts per billion, in the atmosphere above Gale Crater.
Then they divided the area surrounding Gale Crater into six 250 by 250km squares, and looked at the emissions in each square to pin down a location for the source.
"The Mars Express results have been debated before as well, but the new observation technique and analysis ... significantly increases the confidence in the PFS results," Dr Giuranna said.
Mars Express identified the spike in June 2013 but did not detect any high levels of methane after this point — a finding that parallels data from the Curiosity rover.
They did not use the technique to investigate the second spike identified later in the year by Curiosity.
NASA's Dr Webster said it was very rare to have a measurement confirmed.
"This is the same time and location. And it's come from two vastly different instruments; one is an orbiting instrument, the other is a little laser the size of your hand sitting down by the surface."
Dr Webster hoped all three instruments — Curiosity, ExoMars TGO and the Mars Express craft — might be able to detect a pulse at the same time in the future.
"These larger pulses are obviously not a predictable seasonal phenomenon, they are just an occasional sporadic release."
"It would be spectacular if we saw another pulse that is 5 parts per billion or 10 parts per billion."
Mars Express will continue monitoring of the red planet, not just around Gale Crater but other areas too, Dr Giuranna said.
"Our team is involved with the ExoMars Trace Orbiter mission as well and coordinated observations with the PFS are being planned."
Detailed results of the TGO's preliminary findings, presented last year at the American Geophysical Union meeting, are due to be published soon.
Using an instrument onboard the European Space Agency's Mars Express spacecraft, a team of scientists detected a methane spike on June 16, 2013 — backing up observations made a day before by NASA's Curiosity rover.
"A confirmation of measurements is the ultimate prize in planetary exploration," said Chris Webster, who is in charge of Curiosity's methane sensing instrument.
Even more importantly, the Mars Express team has been able to home in on a potential location of the methane spike 500 kilometres to the east of Gale Crater, they report in the journal Nature Geoscience.
A geological survey of the area, known as Aeolis Mensae, identified faults that extend below a region thought to contain shallow ice, said paper co-author Marco Giuranna of the National Institute of Astrophysics in Rome.
"Since permafrost is an excellent seal for methane, it is possible that the ice here could trap subsurface methane and release it episodically along the faults that break through this ice," Dr Giuranna said.
This sporadic belching process happens on Earth, where methane is mainly produced by microorganisms. But the origin of methane on Mars — and potential for life — has long been debated.
While microorganisms may be responsible, 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.
The methane mystery thickens
Mars Express spacecraft first detected a methane spike of 10 parts per billion in the Martian atmosphere in 2004.NASA's Curiosity arrived at the Gale Crater in 2012 and six months passed before any substantial methane was detected, said Dr Webster.
"Curiosity first reported less than 1.3 parts per billion upper limit in the first six months on Mars and we essentially said there's no methane on Mars," Dr Webster said.
It has since detected continual low background levels that peak in the summer months.
But the findings split the science community, with some suggesting that the source of methane may have been Curiosity itself.
"There's no evidence of that whatsoever," Dr Webster said.
Then, late last year, scientists working on the latest spacecraft to sniff out methane on Mars — ExoMars Trace Gas Orbiter (TGO) — reported they'd found no gas in the red planet's atmosphere since observations from the ESA craft began in April last year.
The missing methane had scientists scratching their head.
Spot-tracking technique improves sensitivity
To detect methane, Dr Giuranna and his colleagues — some of whom are also involved in the ExoMars TGO mission — used a new technique called spot-tracking mode.Instead of pointing the instrument, known as the Planetary Fourier Spectrometer (PFS), above the surface and averaging emissions over the entire planet, it locked on to a feature in the landscape and tracked it.
This meant it could pick up local increases in methane.
The instrument detected a spike of 15.2 parts per billion, give or take 2.5 parts per billion, in the atmosphere above Gale Crater.
Then they divided the area surrounding Gale Crater into six 250 by 250km squares, and looked at the emissions in each square to pin down a location for the source.
"The Mars Express results have been debated before as well, but the new observation technique and analysis ... significantly increases the confidence in the PFS results," Dr Giuranna said.
Mars Express identified the spike in June 2013 but did not detect any high levels of methane after this point — a finding that parallels data from the Curiosity rover.
They did not use the technique to investigate the second spike identified later in the year by Curiosity.
NASA's Dr Webster said it was very rare to have a measurement confirmed.
"This is the same time and location. And it's come from two vastly different instruments; one is an orbiting instrument, the other is a little laser the size of your hand sitting down by the surface."
Dr Webster hoped all three instruments — Curiosity, ExoMars TGO and the Mars Express craft — might be able to detect a pulse at the same time in the future.
"These larger pulses are obviously not a predictable seasonal phenomenon, they are just an occasional sporadic release."
"It would be spectacular if we saw another pulse that is 5 parts per billion or 10 parts per billion."
Mars Express will continue monitoring of the red planet, not just around Gale Crater but other areas too, Dr Giuranna said.
"Our team is involved with the ExoMars Trace Orbiter mission as well and coordinated observations with the PFS are being planned."
Detailed results of the TGO's preliminary findings, presented last year at the American Geophysical Union meeting, are due to be published soon.
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