Biology or Geology? –“Scientists Soon to Find Out Why Methane, a Possible Signature of life, is Being Released on Mars” (WATCH Video)


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“We didn’t expect methane to be on Mars, and it shouldn’t be variable unless there is an active source and a vigorous sink,” says Bethany Ehlmann, a planetary scientist at the California Institute of Technology in Pasadena.

For more than a year, reports today's Nature, a 3.5-ton spacecraft has been circling Mars in a series of erratic loops. Now, after 1,000 circuits, the Trace Gas Orbiter (TGO) has reached the ideal position to study the planet’s atmosphere, and has made its first scientific observations. It is poised to solve one of the most controversial mysteries in Martian science: why methane, a possible signature of life, is being released on the red planet.


The TGO is part of the ExoMars mission, a joint venture between the European Space Agency (ESA) and the Russian space agency Roscosmos. The orbiter, which launched in March 2016 and reached the planet that October, is the first craft specifically designed to study gases that make up less than 1% of the planet’s cold, arid atmosphere, including methane, water vapour and ozone. The TGO reached its planned circular orbit earlier this month, and underwent a series of engineering tests before starting to take scientific data on 21 April.



The Martian atmosphere is almost entirely carbon dioxide, but researchers are particularly interested in its other components — especially methane. These trace gases could be signals of biological or geological activity, and they provide clues to the planet’s climatic history.

The Trace Gas Orbiter in a clean room before its launch in 2016. (Thales Alenia Space/ESA)


Scientists have been catching hints of methane in the Martian atmosphere for 15 years using Earth-based telescopes, Mars orbiters and NASA’s Curiosity rover. As evidence of the gas has accumulated, the debate over its origin has intensified. “Nearly 95% of all the methane in the Earth’s atmosphere originated from current and past biology,” says Sushil Atreya, a planetary scientist at the University of Michigan in Ann Arbor. “So, it is natural to ask whether methane on Mars is also of biologic origin.”

The gas’s presence on Mars has surprised researchers, because chemical reactions in the atmosphere should destroy any methane molecules there within a few centuries. A measurable methane level suggests that an active source must be replenishing the gas.

Curiosity now routinely detects a background level averaging 0.5 parts per billion (p.p.b.) of methane in the atmosphere (by contrast, Earth’s level is about 1,875 p.p.b.). But the Martian concentration changes unexpectedly over time, says Atreya. Observations have also suggested the presence of large plumes with concentrations of 45 p.p.b., and Curiosity has detected burps of around 7 p.p.b. that dissipate quickly.

Researchers have suggested several possible sources. The peaks might come from subsurface chemical reactions between rocks and water, carbon-rich meteorites that enter the atmosphere, or from sudden releases from reservoirs beneath Mars’ surface. Most thrilling of all, the peaks could have a biological origin. “It’s really a mystery,” says Ehlmann.

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