Transient clouds in Titan's lower atmosphere (original) (raw)

Nature volume 395, pages 575–578 (1998)Cite this article

Abstract

The 1980 encounter by the Voyager 1 spacecraft with Titan, Saturn's largest moon, revealed1,2 the presence of a thick atmosphere containing nitrogen and methane (1.4 and ∼0.05 bar, respectively). Methane was found to be nearly saturated at Titan's tropopause, which, with other considerations, led to the hypothesis that Titan might experience a methane analogue of Earth's vigorous hydrological cycle, with clouds, rain and seas3,4,5,6,7. Yet recent analyses of Voyager data indicate large areas of supersaturated methane, more indicative of dry and stagnant conditions8,9. A resolution to this apparent contradiction requires observations of Titan's lower atmosphere, which was hidden from the Voyager cameras by the photochemical haze (or smog) in Titan's stratosphere. Here we report near-infrared spectroscopic observations of Titan within four narrow spectral windows where the moon's atmosphere is ostensibly transparent. We detect pronounced flux enhancements that indicate the presence of reflective methane condensation clouds in the troposphere. These clouds occur at a relatively low altitude (15 ± 10 km), at low latitudes, and appear to cover ∼9 per cent of Titan's disk.

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Acknowledgements

We thank C. McKay for conversations on the weather, M. Flasar for suggestions that improved the paper, K. Noll for a helpful reading and C. B. Phillips for help in operating arduous radiative transfer codes. C.G. was supported by an NSF Young Investigator Award, the Research Corporation, and the NASA Planetary Astronomy Program.

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Authors and Affiliations

  1. Department of Physics and Astronomy, Northern Arizona University, PO Box 6010, Flagstaff, 86001-6010, Arizona, USA
    Caitlin A. Griffith & Gary A Miller
  2. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, 96822, Hawaii, USA
    Tobias Owen
  3. Joint Astronomy Centre, 660 N. Aohoku Place, Hilo, 96720, Hawaii, USA
    Thomas Geballe

Authors

  1. Caitlin A. Griffith
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  2. Tobias Owen
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  3. Gary A Miller
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  4. Thomas Geballe
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Correspondence toCaitlin A. Griffith.

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Griffith, C., Owen, T., Miller, G. et al. Transient clouds in Titan's lower atmosphere.Nature 395, 575–578 (1998). https://doi.org/10.1038/26920

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