In the last week of October, the Mars rover Curiosity announced that there was no methane on Mars. The rover’s conclusion is only a preliminary verdict, although it is already controversial because of the implications of the gas’s discovery (or non-discovery).
The presence of methane is an important sign to indicate that life may have existed in the planet’s past. The interest in the notion was increased when Curiosity found signs that water may have flowed in the past through Gale Crater, the immediate neighbourhood of its landing spot, after finding sedimentary settlements.
The rover’s Tunable Laser Spectrometer (TLS), which analysed a small sample of Martian air to come to the conclusion, had actually detected a few parts per billion of methane. However, recognising that the reading was too low to be significant, it sounded a “No”.
In an email to this Correspondent, Adam Stevens, a member of the science team of the NOMAD instrument on the ExoMars Trace Gas Orbiter due to be launched in January 2016, stressed: “No orbital or ground-based detections have ever suggested atmospheric levels anywhere above 50 parts per billion, so we are not expecting to see anything above this level.”
At the same time, he also noted that the 50 parts per billion (ppb) is not a global average. The previous detections of methane found the gas localised in the Tharsis volcanic plateau, the Syrtis Major volcano, and the polar caps, locations the rover is not going to visit. What continues to keep the scientists hopeful is that methane on Mars seems to get replenished by some geochemical or biological source.
The TLS will also have an important role to play in the future. At some point, the instrument will go into a higher sensitivity-operating mode and make measurements of higher significance by reducing errors.
It is pertinent to note that scientists still have an incomplete understanding of Mars’s natural history. As Mr. Stevens noted: “While not finding methane would not rule out extinct or extant life, finding it would not necessarily imply that life exists or existed either.”
Apart from methane, there are very few “bulk” signatures of life that the Martian geography and atmosphere have to offer. Scientists are looking for small fossils, complex carbon compounds and other hydrocarbon gases, amino acids, and specific minerals that could be suggestive of biological processes.
While Curiosity has some fixed long-term objectives, they are constantly adapted according to what the rover finds. Commenting on its plans, Mr. Stevens said, “Curiosity will move up Aeolis Mons, the mountain in the middle of Gale Crater, taking samples and analyses as it goes.”
Curiosity is not the last chance to look more closely for methane in the near future. Development of the ExoMars Trace Gas Orbiter (TGO), with which Mr. Stevens is working, is under way. A collaboration between the European Space Agency and the Russian Federal Space Agency, the TGO is planned to deploy a stationary Lander that will map the sources of methane and other gases on Mars.