Potential Analytical Capabilities The MICA concept, (shown in the figure to the right) incorporates several innovations to reduce power, sample time, mass, and size compared with previous technologies, and eliminate sample preparation and handling. These include: 1) a combination radioisotope source for incident x-rays, 2) a deep depletion CCD detector array to measure x-ray diffraction patterns in two dimensions and fluorescence energies, 3) low-angle scattering from unprepared sample, and 4) visual imaging of the sample. A future flight version of the instrument will also include a miniature translator to move the sampled spot across a rock or soil sample and a miniaturized (40 g) electrical interface module to drive the imaging and x-ray CCDs and acquire data. MICA combines XRD, XRF, and visual analysis techniques for rapid determination of mineralogy and elemental composition of a sample. XRD and can also detect non-crystalline (amorphous) materials. Powder x-ray diffractometry normally needs sample preparation, a com-plex process involving sample acquisition, crushing, sieving, and other physical manipulation. This consumes power, requires sample handling, and is destructive to the sample. The crushing can also change the nature of the sample by causing phase changes in ices from localized melt-ing. The proposed MICA instrument does not require sample acquisition or preparation. The analyses are non-destructive, and the sample remains pristine. The combination of mineral crystal identification (XRD data), elemental abundance (XRF data), and high-resolution images will provide multiple independent but coordinated data for identification and selection of samples for return from an extraterrestrial setting. The rock or soil sample of interest is bombarded at low angle by x-rays, with a beam spot size of 1 mm2. This generates forward-scattered x-ray cones that register as diffraction patterns on the CCD array situated throughout a portion of the 2-theta forward-scattering region. The fluorescence x-rays are also detected and their energy measured using the same CCD. Using a CCD provides several very distinct advantages that are described in more detail be-low. These are: It provides a large reduction in sampling time because all the angular data are accumulated simultaneously instead of scanning, which in turn allows using radioisotope x-ray sources instead of an x-ray tube. It discriminates very effectively against background radiation of all sorts. It measures fluorescent x-rays simultaneously with diffraction x-rays with the same detector. It allows collecting diffraction data over a range of scattering planes instead of just one, resulting in much better capability of identifying single crystallite minerals. Impact of MICA on Sample Return MICA is intended as a screening tool to provide a quick analysis of candidate geological samples, and to aid in selecting samples for a Sample Return mission. It would be equally useful for "sample return" from a field site on Earth to a laboratory for further analysis. The intent is not to conduct standard diffractometry on Mars, rather to define classes of lithology in order to evaluate the geological diversity, and to provide a top-level discrimination tool for selecting samples for return to Earth. In addition to its sample return usefulness it can provide very important survey information to characterize the local environment. If a sample showed unique diffraction patterns and fluorescence data, and was clearly different from others, it would represent a good candidate for return to Earth. Upon return to Earth, the samples may then be further analyzed using the more established, comprehensive, and in-depth analysis techniques available in a terrestrial laboratory. The XRD and XRF data are complemented with a high-resolution camera for acquiring photographic quality images of the samples under analysis. The imaging capability provides a means of positioning the MICA instrument, and provides visual clues of color, texture, struc-tural fabric, granularity, and crystallinity to aid in sample identification and selection. MICA should be able to detect low-Z elements down to carbon, and hence should be sensitive to carbonate minerals. Carbonate samples would be very important to identify because of relevance to planetary weathering processes, the prior existence of liquid water on Mars, and the relation to life forms. Copyright © 2005 N-Science, Inc. Phone: 303-718-9502 - Fax: 303-432-8555 - Email: info@nscicorp.com