Two recent papers by ESE mark new breakthroughs in our understanding of the planet Mars and offer new evidence to suggest that life may exist on our nearest planetary neighbour.

ESE's Breakthroughs On Mars

Two recent papers by ESE mark new breakthroughs in our understanding of the planet Mars and offer new evidence to suggest that life may exist on our nearest planetary neighbour. In a paper published in Geology, Nicholas Warner and Sanjeev Gupta, together with co-workers from University College London, reveal evidence that 3 billion year old thermokarst lakes on the martian surface contained liquid water. The presence of liquid water on Mars is considered an essential prerequiste for the evolution and survival of life on the planet. Meanwhile a new study of the martian atmosphere, published in the journal Earth and Planetary Science Letters, by Richard Court and Mark Sephton, shows that the presence of methane in the martian atmosphere may indicate the presence of extant microbial life on the planet.

The story of life on Mars is also the story of liquid water since aqueous solutions provide the solute for most important biological reactions within living organisms. There are many landforms on Mars that suggest the planet has seen surface liquid water over its long history, however, evidence for lakes has been controversial. Warner and Gupta studied depressions in the Ares Vallis area of Mars that have been suggested to be thermokarst lakes - depressions formed when subterranean permafrost ice melts or sublimates causing subsidence. Although seen elsewhere on Mars such depressions could be form by direct sublimation of ice into water vapour and do not necessarily indicate the presence of liquid water. Warner and Gupta, however, report a new feature not previously identified - the presence of sinuous, shallow channels connecting thermokarst depressions indicating the lakes were once full to over-flowing with water.

The discovery that areas of liquid water, such as thermokarst lakes, existed at least up until 3.0 billion years ago have an important implication for the possibility of life on Mars since together with the warmer earlier periods of the planet's history it implies that there was the opportunity for long-term biological evolution. However, even if life did evolve on Mars, did it survive to the present day? Court and Sephton's study of the origin of methane in the martian atmosphere moves one step closer to being able to answer that very important question.

Methane is present in small but significant amounts in the martian atmosphere and yet does not survive for longer than a few hundred years due to reactions brought about by solar radiation. Methane in the martian atmosphere, therefore, has to be continuously replenished otherwise it would disappear entirely. Previous studies have shown that volcanism is unable to account for martian methane and have suggested that heating of meteorites entering the martian atmosphere could produce the gas. Court and Sephton conducted heating experiments of meteorites to test whether they could produce sufficient methane and found they were unable to produce enough to replenish the martian atmosphere. Two alternative sources of methane are possible. The first is in reactions between volcanic rock and water beneath the surface of Mars. The second is the production of methane by bacteria as a by product of their metabolisms.

“This work is a big step forward" Says Mark Sephton, "As Sherlock Holmes said, eliminate all other factors and the one that remains must be the truth. The list of possible sources of methane gas is getting smaller and excitingly, extraterrestrial life still remains an option. Ultimately the final test may have to be on Mars.”

Associated Personnel 

• Richard Court
• Sanjeev Gupta
• Mark Sephton
• Nicholas Warner