Curiosity findings puzzle Mars rover team

NASA’s Curiosity Mars rover shows the Marias Pass. (Courtesy: NASA/JPL-Caltech/MSSS)

By James Dacey in San Francisco

Rocks rich in silica have been discovered on the surface of Mars, bearing a resemblance to environments on Earth that support microbial life. It’s the latest finding from NASA’s Mars Curiosity rover, presented today in San Francisco at the annual meeting of the American Geophysical Union.

After landing in the Gale crater region of Mars in 2012, NASA’s car-sized rover spent the first couple of years exploring the planes around the elevated region known as Mount Sharp. Since 2014 the rover has started exploring the mountain itself, working its way up from the base.

Around seven months ago, the rover was making its way towards an area called the Marias Pass, checking the composition of rocks by scanning them with a laser from a distance. The moment of excitement arrived when the Curiosity scientists realized their rover had passed an area of rock rich in silica, a substance associated with habitable conditions on Earth. To investigate further, Curiosity did a U-turn to take a closer inspection of some rocks. Up close, Curiosity also deployed its Alpha Particle X-ray Spectrometer and its Chemical and Mineralogy instrument, which studies drilled rock powder.

In the first rock – known as “Buckskin” – the team found tridymite, a mineral rare on Earth and found in specific geological contexts on Earth such as in volcanic ash. The presence of tridymite on Mars, however, has left the Curiosity team puzzled because it does not have an obvious origin in this case. “Mars is not Earth, so we need to think beyond our known geology as to how the tridymite was formed. We are actively pursuing ways to produce it in the lab,” said Liz Rampe, of Aerodyne Industries at NASA’s Johnson Space Center.

High levels of silica were also found at two other study sites located beyond Marias Pass. In these cases, though, the majority was found in opal-A, a mineral that can form in many types of environment – making it more difficult to determine the geological history of the sites. Silica made up 90% of the compositions of some of the rocks analysed.

Harsh conditions make it unlikely that microbial life would be found on Mars today, but this latest finding provides another tantalizing hint that the red planet may have been habitable – to microbial life at least – at some point during its history. Silica-rich environments are often associated with neutral pH environments and the abundance of water is another indication of habitable conditions – as far as we understand life on Earth.

The Curiosity team has two main ideas about how the rocks became so enriched in silica; both theories involve lots of water. The first theory is that acidic water washed away the other rock components, leaving the silica behind. The second idea is that silica dissolved in alkaline or neutral water could have washed through the area and been deposited in the rocks. Either way, further investigation of these rock samples could reveal much more about these former wetlands and their potential for habitability.

“Curiosity was sent to Mars to look for signs of habitability and to investigate how the planet has changed throughout its past. This new finding is a perfect example of the rover doing its job,” said Ashwin Vasavada, of the Mars Science Laboratory Project at NASA’s Jet Propulsion Laboratory.

Find out more about the search for life on Mars by listening to our podcast interview with astrobiologist Lewis Dartnell.