Free Astronomy Magazine

MAY-JUNE 2014 SMALL BODIES crater of this size occurs on Mars only about every 35 to 50 million years, it becomes sta- tistically unlikely the existence of other via- ble shergottites progenitors, unless proving that also far more modest impacts are capa- ble of sending rocks flying into space. A mere time coincidence is not however enough, as it is also necessary to show a min- eralogical correspondence. To pursue this goal, the Werner’s team analyzed data collected by the OMEGA instrument (also known as the Visible and Infrared Mineralo- gical Mapping Spectrometer) aboard the Mars Express spacecraft, and by the CRISM instrument (Compact Reconnaissance Ima- ging Spectrometer for Mars) on the Mars Re- connaissance Orbiter. As a result of the ob- servations by the two spectrometers, both inside and around the wide perimeter bor- der of the Mojave Crater, it was possible to detect the presence of chemical compounds that are typical of shergottites, such as py- roxene and, more in particular, olivine. The correspondence between the proportion and abundance of individual compounds would seem to leave little doubt about the correlation between the Mojave Crater and shergottites. In fact, that is the only structure in terms of size, age and mineralogy that can be a candidate site as the place of origin of shergottites. But there is a problem, by no T he coloured pixels over- laid on this image of the Mojave Crater show the regions where the OMEGA and CRISM instru- ments detected the highest con- centrations of pyroxenes and olivine, whose abundances are consistent with those found in shergottites. [C. Werner et al.] On the side: a section of the Dar al Gani 476 shergottite. [Steve Jurvetson]