The way in which the Mars Science Laboratory rover will identify Martian rocks has been tested by French scientists.

The Mars Science Laboratory rover is due to be launched in 2009. Its overall mission is to determine whether Mars is (or ever was) able to support microbial life. It will carry the ChemCam instrument, which will use laser- induced breakdown spectroscopy (LIBS) to remotely identify Martian rocks.

Jean-Baptiste Sirven, of the CEA Saclay, and his colleagues tested chemometric methods for analysing LIBS spectra. A laser is used to vaporise the dust-covered rock to get to the non-weathered layers below. The elements in the rock are excited by the laser and emit light at characteristic wavelengths. These spectra are then compared to spectra of known samples to classify the rock samples.

Sirven tried three different ways of statistically analysing the spectra. He found that a combination of methods would give the best results. At the start, a method which is able to classify between rocks of very similar composition would be used. Then, as the number of Martian spectra collected increases, a laboratory-calibrated model would become more accurate, as it became more representative of the planet geology. According to Sirven, the combined method correctly identifies over 99% of samples.

Susan Batten