Curiosity Rover Detected Methane on Mars in 2013, a New Analysis Confirms

NASA’s Curiosity rover on Mars.
NASA’s Curiosity rover on Mars.
Image: NASA, JPL-Caltech, MSSS

NASA’s Curiosity rover shook the science community six years ago when it apparently detected traces of methane—an important chemical linked to life—on Mars. Researchers failed to confirm these results in the years that followed, but that’s now changed thanks to a re-analysis of data collected from orbit.

New research published today in Nature Geoscience confirms that NASA’s Curiosity rover detected a methane spike on June 15, 2013, while exploring Gale Crater on Mars. The new paper, led by Marco Giuranna from the Institute for Space Astrophysics and Planetology in Rome, Italy, doesn’t explain how methane came to exist on the Red Planet, but the independent confirmation is a potential sign that Mars once featured conditions suitable for life during its ancient past. More radically, it suggests microbial life once existed on Mars, producing the smelly gas that’s now escaping from the planet’s bowels.

That methane might exist on Mars is an issue of considerable debate. Methane is a key requirement of habitability, and possibly even a signature of life itself. The trouble with methane, however, is that it doesn’t last long in the atmosphere. Any methane that is detected would therefore have been released relatively recently. For Mars, this means the gas is likely venting up from beneath the surface. What’s more, the sporadic, intermittent nature of these apparent methane spikes suggests the methane is being released at irregular intervals.

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Illustration for article titled Curiosity Rover Detected Methane on Mars in 2013, a New Analysis Confirms

Proving that methane exists on Mars would be a huge deal, so scientists have been extra careful to avoid any missteps in this area. The Curiosity detection from 2013 was intriguing, but because the observation could not be corroborated by other instruments, such as in-orbit satellites, it could not be definitively confirmed.

Confirmation of the Curiosity measurement has now happened owing to a re-analysis of data collected by the European Space Agency’s Mars Express orbiter at the time. Specifically, data collected by the spacecraft’s Planetary Fourier Spectrometer on June 16, 2013, when it was above Gale Crater, are in accordance with measurements taken by Curiosity the day before. It’s the first time that measurements made on the ground have been confirmed by a spacecraft in orbit, according to an ESA statement.

Giuranna and his colleagues confirmed the Curiosity observation by looking at 20 months of data collected by Mars Express, and also by developing a new technique that allowed the researchers to scour through hundreds of measurements made over a single area. Interestingly, Mars Express detected no other methane spikes during the observational period aside from the one detected by Curiosity.

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“In general we did not detect any methane, aside from one definite detection of about 15 parts per billion by volume of methane in the atmosphere, which turned out to be a day after Curiosity reported a spike of about six parts per billion,” said Giuranna in a statement “Although parts per billion in general means a relatively small amount, it is quite remarkable for Mars—our measurement corresponds to an average of about 46 tonnes of methane that was present in the area of 49,000 square kilometres observed from our orbit.”

At the time of the Curiosity observation, scientists figured the methane originated north of the rover and was carried to the Gale Crater by southerly winds. The new interpretation presented in the new study offers a different scenario. The quantity of methane detected, along with the geology of the area, suggests the methane spike occurred within Gale Crater itself. Two independent analyses were used to reach this conclusion, including computer simulations that assessed the probability of methane emissions from the Martian surface, and the identification of geological features within Gale Crater consistent with the associated methane spike.

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The hypothesized methane cycle on Mars, showing how the gas is created and destroyed.
The hypothesized methane cycle on Mars, showing how the gas is created and destroyed.
Image: ESA

This kind of thing happens on Earth, typically along tectonic faults and at natural gas deposits. Something similar may be happening on Mars, in this case, along the faults of the Aeolis Mensae region.

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“We identified tectonic faults that might extend below a region proposed to contain shallow ice,” study co-author Giuseppe Etiope from the National Institute of Geophysics and Volcanology said in the ESA statement. “Remarkably, we saw that the atmospheric simulation and geological assessment, performed independently of each other, suggested the same region of provenance of the methane.”

The researchers theorize that the methane detected on Mars is being caused by small, transitory geological events, rather than a process in which the gas is constantly being replenished in the Martian atmosphere. There’s still much to learn about this process, however, such as how the gas is being removed from the atmosphere, and the nature of the Aeolis Mensae site.

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Importantly, the methods used in this new study could lead to the discovery of other methane-producing sites on Mars, which in turn could lead to spots that once, quite possibly, hosted life.

[Nature Geoscience]

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George is a senior staff reporter at Gizmodo.

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DISCUSSION

Before we get excited, it’s worth pointing out that a geological process is the default for explaining how methane is being formed on Mars because we know all the conditions exist for what is known as serpentinisation.

This is the process in which olivine (and more occasionally pyroxene) reacts with carbon dioxide and water to produce the mineral serpentinite as well as magnetite and methane. Olivine is a simple iron-magnesium silicate found in some basalts and other mafic igneous rocks. And Mars has olivine: it is found in shergottite meteorites which have arrived here on Earth.

Carbon dioxide and water are not a problem - there is plenty of both in the Martian atmosphere, lithosphere and cryosphere. If the planet is anything like the Earth, we can also assume there is plenty of water and carbon dioxide still trapped in the Mantle.

In chemistry terms (digs up ancient MSc notes), the main process of serpentinisation is:

18Mg2SiO4 + 6Fe2SiO4 + CO2 + 26H2O + -> 12Mg3Si2O5(OH)4 + 4Fe3O4 + CH4

In English:

magnesium olivine + iron olivine (natural olivine is a mixture of magnesium and iron silicate) + carbon dioxide + water -> serpentinite + magnetite + methane.

Serpentinisation requires some heat to get started, but it is perfectly reasonable to assume the deeper Crust and Upper Mantle of Mars are both still hot even though surface volcanism appears to have ended or is very minor. However, serpentinisation generates heat so it becomes a self-sustaining reaction.

The methane would rise up through faults and fractures in the Martian rock to enter the atmosphere - perhaps the persistent plumes seen by ESA’s Trace Gas Orbiter and ISRO’s Mangalyaan mark faults or vents reaching deep into the interior. And there might be other forces such as weak tectonic activity or even the changing seasons that cause changes in the amount of methane escaping to the atmosphere.

Probably the best way of finding out the origin of the methane will be to take a mass spectrometer to Mars. If Martian life exists and is anything like Earth’s, it will preferably metabolise 12carbon over the slightly heavier 13carbon which means living organisms and their byproducts are enriched in 12carbon compared to inorganic carbon. However, if the methane is coming from geological processes there should be no enrichment in 12carbon.