ExoMars X-ray Diffraction Instrument

ExoMars is a robotic mission developed by the European Space Agency.  As part of the ‘Mars Joint Exploration Initiative’ with NASA, ExoMars will launch in 2018 and land on the surface of Mars with mission objectives to study the surface in terms of past or present water and search for traces of martian life.

Mars analogue sample being loaded into the Space  Research Centre laboratory XRD chamber between the X-ray source and CCD.

We are contributing towards at least three instruments that will be carried aboard the ExoMars rover, one of which is the Mars X-ray Diffractometer (Mars XRD).   Other instrumets are Raman and the Life Marker Chip.   Calibration and testing of the Mars XRD technique is being done at the SRC, investigating the method and the instrument's ability to identify the mineralogy of unknown rock and soil samples.  We are performing laboratory testing with standard reference and martian analogue materials.  We are investigating the effects of changing X-ray incidence angles and detector geometry on the XRD and X-ray Fluorescence (XRF).  XRD allows  identification of mineral structure, and the XRF observes the fluorescent X-rays emitted by the sample as the atoms within are excited by the high-energy X-ray source, thus allowing the determination of chemical composition. 

When martian soil is retrieved, either from the surface or collected by the ExoMars drill from depths of up to 2 metres, it will be brought inside the rover where the internal XRD instruments can analyse the sampled material.  The XRD instrument, in the SRC laboratory, resides within a chamber which simulates the same near vacuum and freezing conditions that will be expected for the internal instruments of the ExoMars rover.  Using a radioactive Fe-55 source, the X-ray beam is targeted at the sample with the observing CCD positioned to receive the X-ray diffraction and fluorescence from the sample.  The surface of the sample can be tilted, and the CCD repositioned, to the required setup within the constraints of the instrument.  ExoMars will have three static CCDs already positioned correctly within the rover.

The Mars XRD, carried on the ExoMars rover, will be one of the first X-ray Diffractometers to be used in a non-terrestrial environment.  This will be an achievement, for compared to the typically large size and 100 kg weight of laboratory XRD instruments used by geologists here on planet Earth, the ExoMars XRD will be of a very much reduced size and weight of just 0.8 kg or less.