A version of this story, as written by me, appeared in The Hindu on November 15, 2012.
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 one of the most important prerequisites for life to 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 10-30 parts per billion, so we are not expecting to see anything above this level.”
At the same time, he also noted that the 10-30 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.”
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 definitely 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, however.
On the other side of the Atlantic, development of the ExoMars Trace Gas Orbiter (TGO), with which Mr. Stevens is working, is underway. 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.
Its observations will contribute to selecting a landing site for the ExoMars rover due to be launched in 2018.
Even as Curiosity completed 100 days on Mars on November 14, it still has 590 days to go. However, it has also already attracted attention from diverse fields of study. There is no doubt that from the short trip from the rim of Gale Crater, where it is now, to the peak of Aeolis Mons, Curiosity will definitely change our understanding of the enigmatic red planet.