Storm clouds on Saturn: Lightning-induced chemistry and associated materials consistent with Cassini/VIMS spectra
Planetary and Space Science
By: K. H. Baines, M.L. Delitsky, T.W. Momary, R. H. Brown, B. J. Buratti, R. N. Clark, and P. D. Nicholson
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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.
Suggested Citation
Baines, K.H., Delitsky, M., Momary, T., Brown, R.H., Buratti, B.J., Clark, R.N., and Nicholson, P.D., 2009, Storm clouds on Saturn: Lightning-induced chemistry and associated materials consistent with Cassini/VIMS spectra: Planetary and Space Science, v. 57, no. 14-15, p. 1650-1658, https://doi.org/10.1016/j.pss.2009.06.025.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Storm clouds on Saturn: Lightning-induced chemistry and associated materials consistent with Cassini/VIMS spectra |
| Series title | Planetary and Space Science |
| DOI | 10.1016/j.pss.2009.06.025 |
| Volume | 57 |
| Issue | 14-15 |
| Year Published | 2009 |
| Language | English |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Planetary and Space Science |
| First page | 1650 |
| Last page | 1658 |