Opening ceremony, UNESCO Paris, 21 January 2014

David Bish, Indiana University, CheMin Instrument Team


The first X-ray diffraction results from another planet

David Bish


The Mars Science Laboratory (MSL) began its journey to Mars in November 2011, landing in Gale Crater on the night of 5 August 2012. Gale Crater is occupied by Mt Sharp at the center, three times higher than the Grand Canyon (USA) is deep.

MSL carries ten instruments on, or inside, the Curiosity rover, including CheMin, a miniature X-ray diffraction (XRD) and fluorescence (XRF) instrument. XRD is a well-established technique on Earth, using much larger laboratory instruments. It can provide more accurate identifications of minerals than any method previously used on the Red Planet. Curiosity delivered sieved (150 μm) samples of soil to the shoebox-size CheMin and the first XRD data were successfully measured on Mars in October 2012, coinciding with the 100th anniversary year of the discovery of XRD by von Laue.

The CheMin instrument first analysed a sample of Martian soil/dust from a dune and found that it is very similar to soils on the flanks of Mauna Kea volcano in Hawaii, containing minerals commonly found in basalts, along with amorphous or glassy material. No clay minerals were discovered in the soil, suggesting an absence of interaction with liquid water.

Subsequent XRD analyses of drilled rocks revealed the presence of clay minerals, in addition to minerals found in basalt. The level of mineralogical detail provided by CheMin was previously unobtainable and provides information on rock formation conditions. Clay minerals are consistent with formation in water. Moreover, the age of these rocks shows that Mars hosted wet environments more recently than previously thought. In addition, the particular minerals found in the drilled rocks are compatible with an environment that was potentially habitable to life, with near-neutral pH and moderate temperatures.


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