Mathematics – Logic
Scientific paper
Sep 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.0409b&link_type=abstract
American Astronomical Society, DPS meeting #28, #04.09; Bulletin of the American Astronomical Society, Vol. 28, p.1071
Mathematics
Logic
Scientific paper
We consider how to best look for frozen SO_2 and H_2S on Europa with Galileo's Near Infrared Mapping Spectrometer (NIMS), in part by creating simulated NIMS spectra based upon our lab spectroscopic reflectance data [e.g. 1,2] of H_2S, SO_2, and H_2O ices. The presence or absence, abundance, and location of SO_2 or H_2S on Europa could have significant implications for understanding Europa's geologic and even biologic history. IUE and HST data of Europa show a band in the UV that [3] interpret as most likely due to frozen SO_2; and [4] interpret continuum slope of UV/Visible data as consistent with sulfur compounds or allotropes. In groundbased data, many of the strongest SO_2 and H_2S bands overlap with Europa's saturated 3 mu m water ice band. Even so, [5,6] indicate some SO_2 bands near 4 mu m may be barely visible. With better spatial resolution and sensitivity, NIMS may be able to detect SO_2 using the strong 4.1 mu m band, particularly in areas that are enriched in SO_2 or depleted somewhat in water ice relative to global averages. Perhaps even better to look for is the weaker SO_2 2.54 mu m band because it lies outside the main water bands. It is much weaker than the 4 mu m SO_2 band, but strong enough that it should be visible in pixels where SO_2 averages a mm or more in thickness on the surface [1]. H_2S will be a challenge to observe because the optimum bands, near 3.9 and 2.7 mu m, both overlap with spectral areas saturated by water ice in groundbased data. However, even thin (0.1 to 1 mm) H_2S frosts create very deep bands at these wavelengths [7], and NIMS' vastly better spatial resolution, as well as greater sensitivity, may allow looking for these bands. References. [1] Nash, D. B. and B. H. Betts, Icarus, 117, 402-419, 1995. [2] Nash, D. B. and R. Howell, Science, 244, 454-457, 1989. [3] Noll, K. S. et al., J. Geophys. Res., 100, 19057-19060, 1995. [4] Spencer et al., J. Geophys. Res., 100, 19049-19056, 1995. [5] Calvin, W. M. et al., J. Geophys. Res., 100, 19041-19048, 1995. [6] Lebofsky and Feierberg, Icarus, 63, 237-242, 1985. [7] Betts, B. H. and D. B. Nash, LPSC XXVII, 109-110, 1996.
Betts Bruce H.
Nash Douglas B.
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