An artist’s impression showing the ExoMars Trace Gas orbiter using repeated dips into the upper atmosphere of Mars, a technique known as aerobraking, to reach its intended science orbit. Recent observations indicate a surprising absence of methane in the red planet’s atmosphere. Image: ESA
The ESA-Roscosmos ExoMars Trace Gas Orbiter – TGO – spacecraft has found a surprising lack of methane in the martian atmosphere. In fact, the spacecraft’s two spectrometers, NOMAD and ACS, found 10 to 100 times less methane than all previously reported detections by a variety of spacecraft and ground-based telescopes.
Martian methane is an area of high interest because it can be a signature of biological activity. It also can be produced by geological processes, but either way, solar radiation acts to destroy it over relatively short timescales. As a result, any detections indicate recent activity. That’s true even if the methane was generated millions to billions of years ago and remained trapped in sub-surface reservoirs until now.
On Earth, 95 percent of all the methane in the atmosphere was produced by biological processes. The concentration is about 18 parts per billion by volume, or ppbv, meaning that out of every one billion molecules, 1,800 are ...