NASA's Mars Rover Opportunity has now been travelling across the surface of the red planet for eight years, covering a total of more than 33 kilometres on the journey from its landing site to the rim of the crater known as 'Endeavour'.
Late last year Opportunity came across what appeared to be veins of gypsum at the edge of the crater, which is 22 kilometres across and allows access to older layers of rock than the sulfur-rich sandstone on the surface surrounding the landing site.
The results of the study on the geology of the site, led by Steve Squyres of Cornell University in Ithaca, have recently been published in Science
. While many of the rock samples collected were from meteorites, others were discovered to have originated from impact craters other than the Endeavour crater. The rock at the crater edge was found to be akin to suevite, a type of impactite rock which takes its name from Swabia, after the area of southern Germany where it was first identified.
Suevite is a composite of silicates made molten by meteorite impact, fragments of rock, and minerals only created at extremely high temperatures. The Nördlinger Ries crater in Germany – where suevite was originally found – is of a similar size to Endeavour, but is much younger as it was formed only 15 million years ago, as opposed to the 3.7 billion year age of its Martian cousin.
The researchers were able to test the constituent elements in the rock samples with the use of Rover's alpha-particle X-ray spectrometer (APXS). The instrument was developed at the Max Planck Institute for Chemistry in Mainz and is undergoing further work at the University of Guelph in Canada at the hands of Ralf Gellert's team. It was APXS analysis which identified the presence of the gypsum vein.
O) is formed only when water is present and at a temperature below 60ºC. The finding implies that conditions once existed on Mars that would have been conducive to life. Had the temperature been higher, anhydrite (CaSO4
) would have been found, and had sulfur been present in sufficient amounts, the sulfurous sandstone found elsewhere on the planet would also have been present.
The fact that gypsum was instead formed indicates that water circulated through cracks in the rock after the meteorite which made the crater struck, providing further evidence for the one-time presence of water and the tantalising prospect of life on Mars.