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

Kevin H. Baines, Mona L. Delitsky, Thomas W. Momary, Robert H. Brown, Bonnie J. Buratti, Roger N. Clark, Philip D. Nicholson

Research output: Contribution to journalArticlepeer-review

38 Scopus citations

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 μm to at least 4.1 μm. 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 μm 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.

Original languageEnglish (US)
Pages (from-to)1650-1658
Number of pages9
JournalPlanetary and Space Science
Volume57
Issue number14-15
DOIs
StatePublished - Dec 1 2009

Keywords

  • Cassini-huygens
  • Lightning chemistry
  • Saturn:clouds
  • Saturn:lightning
  • Thunderstorm
  • Visual-infrared mapping spectrometer (VIMS)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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