Mars rover finds conditions once suited for ancient life

Published by University of Leicester Press Office for University of Leicester in Education

Leicester planetary scientist involved in discovery of clay samples in Mars rock

An analysis of a rock sample collected by NASA's Curiosity rover shows ancient Mars could have supported living microbes.

Scientists identified sulphur, nitrogen, hydrogen, oxygen, phosphorus and carbon -- some of the key chemical ingredients for life -- in the powder Curiosity drilled out of a sedimentary rock near an ancient stream bed in Gale Crater on the Red Planet last month.

Dr John Bridges, of the University of Leicester’s Space Research Centre within the Department of Physics and Astronomy, is one of two UK Participating Scientists on the mission, and leads a team from the University of Leicester, the Open University and CNRS France.

He worked with other members of the Mars Science Laboratory mission to decide where the rover should drill.

Clues to this habitable environment come from data returned by the rover's Sample Analysis at Mars (SAM mass spectrometer) and Chemistry and Mineralogy (CheMin X-ray diffraction) instruments.

The data indicate the Yellowknife Bay area the rover is exploring was at the end of an ancient river system or an intermittently wet lake bed that could have provided chemical energy and other favourable conditions for microbes.

The rock is made up of a fine-grained mudstone containing clay minerals, sulphate minerals and other chemicals. This ancient wet environment, unlike some others on Mars, was not harshly oxidizing, acidic or extremely salty.

The bedrock also is fine-grained mudstone and shows evidence of multiple periods of wet conditions, including nodules and veins.  Curiosity's drill collected the sample at a site just a few hundred metres away from where the rover earlier found an ancient streambed in September 2012.

These clay minerals are a product of the reaction of relatively fresh water with igneous minerals, such as olivine, also present in the sediment. The reaction could have taken place within the sedimentary deposit, during transport of the sediment, or in the source region of the sediment.

Scientists were surprised to find a mixture of oxidized, less-oxidized, and even non-oxidized chemicals, providing an energy gradient of the sort many microbes on Earth exploit to live. This partial oxidation was first hinted at when the drill cuttings were revealed to be grey rather than red.

An additional drilled sample is planned to be used to help confirm these results for several of the trace gases analysed by the SAM instrument.

Dr Bridges said: “This is the first time we have found large amounts of clay on Mars. The rocks are similar to terrestrial mudstones which form in standing bodies of water.  We also find similar clay – though less abundant and in veins – within some martian meteorites.

“We know from the composition of the clay that it formed in neutral to mildly alkaline conditions and at the sort of temperatures that on Earth we associate with habitability for microbial life.

“We have never seen anything like this at the previous landing sites and it is telling us that some localities on Mars were habitable. Whether they were inhabited remains another question - perhaps we will need the dedicated instruments of ExoMars or Mars Sample Return to firmly establish that.”

Michael Meyer, lead scientist for NASA's Mars Exploration Program at the agency's headquarters in Washington, said: “A fundamental question for this mission is whether Mars could have supported a habitable environment. From what we know now, the answer is yes.”

Scientists plan to work with Curiosity in the "Yellowknife Bay" area for many more weeks and wait for a communication-blocking planetary conjunction between Earth, Mars and the Sun to pass in April, before beginning a 8.5 km drive to Gale Crater's central mound, Mount Sharp. Investigating the stack of layers exposed on Mount Sharp, where clay minerals and sulphate minerals have been identified from orbit, may add information about the duration and diversity of habitable conditions.

Curiosity, carrying 10 science instruments, landed seven months ago to begin its two-year prime mission. NASA's Jet Propulsion Laboratory in Pasadena, California, manages the project for NASA's Science Mission Directorate in Washington.