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Direct detection of variable tropospheric clouds near Titan's south pole

Abstract

Atmospheric conditions on Saturn's largest satellite, Titan, allow the possibility that it could possess a methane condensation and precipitation cycle with many similarities to Earth's hydrological cycle. Detailed imaging studies1,2,3,4 of Titan have hitherto shown no direct evidence for tropospheric condensation clouds, although there has been indirect spectroscopic evidence for transient clouds5,6. Here we report images and spectra of Titan that show clearly transient clouds, concentrated near the south pole, which is currently near the point of maximum solar heating. The discovery of these clouds demonstrates the existence of condensation and localized moist convection in Titan's atmosphere. Their location suggests that methane cloud formation is controlled seasonally by small variations in surface temperature, and that the clouds will move from the south to the north pole on a 15-year timescale.

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Figure 1: Images of Titan show the transient existence of cloud features near the south pole.
Figure 2: The transient polar clouds are best seen in polar projections of the images of Titan.
Figure 3: Spatially resolved spectra of the disk of Titan showing the height in the atmosphere of the transient features.

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Acknowledgements

We thank E.J. Moyer and M.I. Richardson for conversations, D. Le Mignant, R. Campbell, M. Konacki and J. Eisner for acquiring the NIRC2 data, and S. Hörst for many nights of monitoring Titan in the cold. This work was supported by a grant from the NSF Planetary Astronomy programme.

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Correspondence to Michael E. Brown.

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Brown, M., Bouchez, A. & Griffith, C. Direct detection of variable tropospheric clouds near Titan's south pole. Nature 420, 795–797 (2002). https://doi.org/10.1038/nature01302

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