REMOTE X-RAY DIFFRACTION AND X-RAY FLUORESCENCE ANALYSIS ON PLANETARY SURFACES, D.F. Blake, pp. 487-496

The legacy of planetary X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) began in 1960 when W. Parish proposed an XRD instrument for deployment on the moon. The instrument was built and flight qualified, but the Lunar XRD program was cancelled shortly before the first human landing in 1969. XRF chemical data have been collected in situ by surface landers on Mars (Viking 1 & 2, Pathfinder) and Venus (Venera 13 & 14). These highly successful experiments provide critical constraints on our current understanding of surface processes and planetary evolution. However, the mineralogy, which is more critical to planetary surface science than simple chemical analysis, will remain unknown or will at best be imprecisely constrained until Xray diffraction (XRD) data are collected. Recent progress in X-ray detector technology allows the consideration of simultaneous XRD (mineralogic analysis) and high-precision XRF (elemental analysis) in systems miniaturized to the point where they can be mounted on fixed landers or small robotic rovers. There is a variety of potential targets for XRD/XRF equipped landers within the solar system, the most compelling of which are the poles of the moon, the southern highlands of Mars and Europa. REMOTE SENSING OF SOLAR SYSTEM OBJECTS Remote spectral analysis techniques have been applied to many objects within our solar system, with the result that in general terms, we know the compositions of the solid surfaces that we can image. In some instances, high-resolution spectral data are available as is the case for the Moon, Mars, and Europa, among others. However, even these high-resolution images and analyses have lateral spatial resolutions of tens to thousands of meters, orders of magnitude larger than the scale length of the phases (e.g., minerals) which comprise the images. The elemental / chemical information obtained by remote sensing, while informative, has spawned a cottage industry of studies of analog materials and a myriad of interpretations. Remote sensing is principally useful in the formulation of hypotheses that can later be investigated by in-situ analysis techniques. There is a wide variety of objects in our solar system to which in-situ instrument packages could be profitably deployed: • The rocky planets Mercury, Venus and Mars, • Rocky planetesimals, including asteroids and planetary moons, • Icy planetesimals, including Kuiper belt objects, Oort cloud comets and icy moons Copyright(c)JCPDS-International Centre for Diffraction Data 2000,Advances in X-ray Analysis,Vol.43 487