Storm clouds on Saturn: Lightning-induced chemistry and associated materials consistent with Cassini/VIMS spectra

Baines, K. H.; Delitsky, M. L.; Momary, T. W.; Brown, R. H.; Buratti, B. J.; Clark, R. N.; Nicholson, P. D.

Abstract:

Thunderstorm activity on Saturn is associated with optically detectable clouds that are atypically dark throughout the near-infrared. As observed by Cassini/VIMS, these clouds are ~20% less reflective than typical neighboring clouds throughout the spectral range from 0.8 ??m to at least 4.1 ??m. We propose that active thunderstorms originating in the 10-20 bar water-condensation region vertically transport dark materials at depth to the ~1 bar level where they can be observed. These materials in part may be produced by chemical processes associated with lightning, likely within the water clouds near the ~10 bar freezing level of water, as detected by the electrostatic discharge of lightning flashes observed by Cassini/RPWS (e.g., Fischer et al. 2008, Space Sci. Rev., 137, 271-285). We review lightning-induced pyrolytic chemistry involving a variety of Saturnian constituents, including hydrogen, methane, ammonia, hydrogen sulfide, phosphine, and water. We find that the lack of absorption in the 1-2 ??m spectral region by lightning-generated sulfuric and phosphorous condensates renders these constituents as minor players in determining the color of the dark storm clouds. Relatively small particulates of elemental carbon, formed by lightning-induced dissociation of methane and subsequently upwelled from depth - perhaps embedded within and on the surface of spectrally bright condensates such as ammonium hydrosulfide or ammonia - may be a dominant optical material within the dark thunderstorm-related clouds of Saturn. ?? 2009 Elsevier Ltd. All rights reserved.

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Article

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70036055

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Baines, K. H.; Delitsky, M. L.; Momary, T. W.; Brown, R. H.; Buratti, B. J.; Clark, R. N.; Nicholson, P. D.

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1658

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14-15

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English

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Planetary and Space Science

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Storm clouds on Saturn: Lightning-induced chemistry and associated materials consistent with Cassini/VIMS spectra; 2009; Article; Journal; Planetary and Space Science; Baines, K. H.; Delitsky, M. L.; Momary, T. W.; Brown, R. H.; Buratti, B. J.; Clark, R. N.; Nicholson, P. D.