COMPARISON OF LABORATORY EMISSION SPECTRA WITH MERCURY TELESCOPIC DATA



ANN L. SPRAGUE

Lunar and Planetary Laboratory
University of Arizona, Tucson, AZ 85721
sprague
fax 520-621-4933


T.L.ROUSH

Dept. of Geosciences, San Francisco State Univ., CA 94132
troush@mail.arc.nasa.gov



ABSTRACT

(ICARUS 133, 174-183, 1998)


Thermal emission spectra from four locations on Mercury's surface are compared with three new laboratory emission spectra: two spinels (gahnite and magnetite) and one carbonaceous chondrite (Allende). The mineral and meteorite choices were made to investigate previously suggested unique scenarios for the evolution of Mercury's surface. No resemblance of the Mercury data were seen to the measured emission spectra. We also compare Mercury spectra to a selection of inverted reflectance spectra of feldspars, feldspathoids, Apollo 16 lunar breccias, nepheline-bearing alkali syenite and simple two-component linear mixes of feldspars and pyroxenes. The Mercury spectra obtained from locations centered near 40o and 45o mercurian longitude and equatorial latitudes are concave upward in shape between 8 and 10m like that of nepheline but the emissivity maxima of the data occur at shorter wavelength than any of the feldspathoids (nepheline, leucite, sodalite). A good match of the wavelength position of Mercury's emissivity maxima is provided by the nepheline-bearing alkali syenite. Comparisons to several feldspars in the plagioclase series, and plagioclase and pyroxene lunar breccia (67031 and 67455), and to linear mixing models of plagioclase and pyroxene, provide good matches to some features near ~120o and ~34o mercurian longitude and equatorial latitudes. More conclusive interpretation of these data from Mercury requires laboratory studies of emission spectra obtained specifically for thermal and insolation conditions appropriate for airless bodies.