Life on Mars? Not likely

While May 25, 2008 – the date of the Phoenix lander’s descent onto Mars’ surface – may be a day long forgotten for most, the same cannot be said of Dr Tom Pike of the Department of Electrical and Electronic Engineering at Imperial College London and his team, who, for the last three years, have been analysing data provided by the lander, along with colleagues. The results of their work were discussed at a European Space Agency meeting last Tuesday.

The team of researchers analysed soil samples using optical and atomic force microscopes, allowing them to resolve particles with diameters of as little as 100 microns. They have since been diligently cataloguing the particle sizes present in the sample. The particles’ make-up and distribution reveals key information about the formation of Martian soil and its interaction with liquid water.

The researchers searched for clay particles formed by the chemical process of water breaking down rock. No evidence of such microscopic particles was found. Even when making the assumption that all particles within the size range comparable to analogous particles in Earth’s soil were clay, these would only make up about 0.1% of Martian soil. Comparing this to Earth’s soil, where clay content can be as high as 5%, suggests that Mars’ surface has a very arid history, unfavourable for the development of life.

The particle size distribution (PSD) of soil being studied can be used to draw conclusions about its exposure to liquid water because the proportion of clays depends mostly on length of water exposure and the conditions thereof. In the case of the samples of Martian soil studied, this analysis revealed that the soil could not have been in contact with liquid water for a total of any more than 5000 years throughout the planet’s 4.6 billion years of history. This window of time, even when assuming that the 5000 years occurred in one continuous period, is too short to reasonably expect life to have formed.

In fact, the PSD of Martian soil matches that of the Moon more closely than that of Earth; it shows signs of extreme physical weathering during its formation. While on the Moon, which is not protected by an atmosphere, this is likely due to frequent collisions with meteorites, Martian soil is weathered mostly by strong winds, again suggesting a very hostile environment.

While this study examined only samples from Phoenix’s landing site, close to the northern polar cap, satellite images suggest that there is little variation in the soil’s consistency between different areas of the globe. The same conclusion may thus be drawn for the planet as a whole.

However, all hope is not yet lost. Previous research showed that Mars likely had a warmer, wetter period earlier in its history. This would have been more suited for the development of life. To find out more, scientists must dig deeper and look beyond the surface – literally. Life may still be “taking refuge underground,” Pike says. More research is necessary before the idea of life on Mars can be dismissed entirely.

DOI:10.1029/2011GL049896