Roving on Mars
Crystallography has provided insight into the fundamental structure of matter on earth, but it now plays a critical role in the exploration of other planets. X-ray crystallography, a standard practice for geologists, is central to Martian exploration of NASA’s Mars Rover, Curiosity. Through crystallography the rover aims to unlock the geological history of Mars, determine when water existed on its surface, and look at the planet’s ability to sustain life.
A few billion years ago, Mars and Earth were rather alike with respect to chemical composition. It is possible that Mars had oceans like Earth and many fine surface details corroborate the geologically recent occurrence of streaming water. The geological similarities between the two planets ignited questions about Mars’ aqueous history and its potential, both historically and current, to host life.
A very considerable part of the solid material in the universe is crystalline and x-ray crystallography provides a powerful analytical method to identify and quantitatively characterise crystalline solids. The process is used to reveal a mineral’s atomic and molecular structure by recording how its crystals distinctively interact with x-rays. Through measuring the angles and intensities of diffracted x-ray beams, it is possible to produce a 3D picture of the atomic and molecular arrangement of the analysed materials. It is precisely this process that is being used on Mars today and has revolutionised planetary exploration.
NASA’s Rover Curiosity, landed in Gale Crater on Mars 5 August 2012. The rover was equipped with instruments to collect information on the climate and geology, and investigate the role of water on Mars’ surface. This included an x-ray diffraction and fluorescence instrument called CheMin (Chemistry and Mineralolgy). With innovations form Ames, CheMin was created to be compact enough to fit in the rover - providing the most accurate analysis of Mars’ surface ever attempted.
The first sample taken by Curiosity was of dust and sand, located in a region called Rocknest. It was sieved to remove particles larger than 150 micrometers (about the width of a human hair). The results from CheMin revealed that the mineralogy of the Martian soil was similar to weathered basaltic soil flanking Mauna Kea volcano in Hawaii.
Although the first sample made scientific history, it lacked clay minerals, suggesting that the sand or dust had not interacted with water. Clay minerals are crucial in the search of water because they only form in its presence. These windblown deposits were the result of current geological processes on Mars’ surface, too recent to solve Curiosity’s query. Close by, Mt Sharp would provide a deeper look into Mars’ geological history.
Found within Gale crater, Mt Sharp reaches 5,500 meters; the mountain appears to consist of eroded sedimentary layers deposited over a 2 billion year interval. Drilled samples taken by Curiosity confirmed the presence of clay minerals along with other basaltic minerals. Through x-ray crystallography, it is clear that at some point in its history, Mars hosted aqueous environments. It is also evident that wet environments existed more recently than previously thought. The clay minerals indicate near-neutral pH environment and moderate temperatures – the key ingredients for life.
Identifying the mineralogical makeup of Mars and understanding the conditions in which these minerals formed, would not be possible without x-ray crystallography. Through this type of analysis, it has been confirmed that Mars has hosted the key to life - water. From here, future goals for Curiosity include exploring Mt Sharp. Taking samples from its varied layers will help piece together a more complete geological history of the Red Planet.
