Saturn’s moon Titan has a dense nitrogen-rich atmosphere, with methane as its primary volatile. Titan’s atmosphere experiences an active chemistry that produces a haze of organic aerosols that settle to the surface and a dynamic climate in which hydrocarbons are cycled between clouds, rain and seas. Titan displays particularly energetic meteorology at equinox in equatorial regions, including sporadic and large methane storms. In 2009 and 2010, near Titan’s northern spring equinox, the Cassini spacecraft observed three distinctive and short-lived spectral brightenings close to the equator. Here, we show from analyses of Cassini spectral data, radiative transfer modelling and atmospheric simulations that the brightenings originate in the atmosphere and are consistent with formation from dust storms composed of micrometre-sized solid organic particles mobilized from underlying dune fields. Although the Huygens lander found evidence that dust can be kicked up locally from Titan’s surface, our findings suggest that dust can be suspended in Titan’s atmosphere at much larger spatial scale. Mobilization of dust and injection into the atmosphere would require dry conditions and unusually strong near-surface winds (about five times more than estimated ambient winds). Such strong winds are expected to occur in downbursts during rare equinoctial methane storms—consistent with the timing of the observed brightenings. Our findings imply that Titan—like Earth and Mars—has an active dust cycle, which suggests that Titan’s dune fields are actively evolving by aeolian processes.
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VIMS data are available via NASA’s Planetary Data System (PDS): http://pds-atmospheres.nmsu.edu/data_and_services/atmospheres_data/Cassini/vims.html. The data that support the analysis and plots within this paper and other findings of this study are available from the corresponding author upon request.
Turtle, E. P. et al. Cassini imaging of Titan’s high-latitude lakes, clouds, and south-polar surface changes. Geophys. Res. Lett. 36, L2204 (2009).
Rodriguez, S. et al. Global circulation as the main source of cloud activity on Titan. Nature 459, 678–682 (2009).
Rodriguez, S. et al. Titan’s cloud seasonal activity from winter to spring with Cassini/VIMS. Icarus 216, 89–110 (2011).
Turtle, E. P. et al. Seasonal changes in Titan’s meteorology. Geophys. Res. Lett. 38, L03203 (2011).
Turtle, E. P. et al. Rapid and extensive surface changes near Titan’s equator: evidence of April showers. Science 331, 1414–1417 (2011).
Barnes, J. W. et al. Precipitation-induced surface brightenings seen on Titan by Cassini VIMS and ISS. Planet. Sci. 2, 1 (2013).
Rannou, P., Montmessin, F., Hourdin, F. & Lebonnois, S. The latitudinal distribution of clouds on Titan. Science 311, 201–205 (2006).
Mitchell, J. L. The drying of Titan’s dunes: Titan’s methane hydrology and its impact on atmospheric circulation. J. Geophys. Res. Planets 113, E08015 (2008).
Schneider, T., Graves, S. D. B., Schaller, E. L. & Brown, M. E. Polar methane accumulation and rainstorms on Titan from simulations of the methane cycle. Nature 481, 58–61 (2012).
Lora, J. M., Lunine, J. I. & Russell, J. L. GCM simulations of Titan’s middle and lower atmosphere and comparison to observations. Icarus 250, 516–528 (2015).
Mitchell, J. L. & Lora, J. M. The climate of Titan. Annu. Rev. Earth Planet. Sci. 44, 353–380 (2016).
Schaller, E. L., Roe, H. G., Schneider, T. & Brown, M. E. Storms in the tropics of Titan. Nature 460, 873–875 (2009).
Griffith, C. A. et al. Characterization of clouds in Titan’s tropical atmosphere. Astrophys. J. 702, L105–L109 (2009).
Lorenz, R. D. et al. The sand seas of Titan: Cassini RADAR observations of longitudinal dunes. Science 312, 724–727 (2006).
Rodriguez, S. et al. Global mapping and characterization of Titan’s dune fields with Cassini: correlation between RADAR and VIMS observations. Icarus 230, 168–179 (2014).
Brown, R. H. et al. The Cassini Visual and Infrared Mapping Spectrometer investigation. Space Sci. Rev. 115, 111–168 (2004).
Lorenz, R. D. Pillow lava on Titan: expectations and constraints on cryovolcanic processes. Planet. Space Sci. 44, 1021–1028 (1996).
Davies, A. G. et al. Atmospheric control of the cooling rate of impact melts and cryolavas on Titan’s surface. Icarus 208, 887–895 (2010).
Hirtzig, M. et al. Titan’s surface and atmosphere from Cassini/VIMS data with updated methane opacity. Icarus 226, 470–486 (2013).
Soderblom, L. A. et al. Correlations between Cassini VIMS spectra and RADAR SAR images: implications for Titan’s surface composition and the character of the Huygens probe landing site. Planet. Space Sci. 55, 2025–2036 (2007).
Barnes, J. W. et al. Spectroscopy, morphometry, and photoclinometry of Titan’s dunefields from Cassini/VIMS. Icarus 195, 400–414 (2008).
Clark, R. N. et al. Detection and mapping of hydrocarbon deposits on Titan. J. Geophys. Res. Planets 115, E10005 (2010).
Le Gall, A. et al. Cassini SAR, radiometry, scatterometry and altimetry observations of Titan’s dune fields. Icarus 213, 608–624 (2011).
Bonnefoy, L. E. et al. Compositional and spatial variations in Titan dune and interdune regions from Cassini VIMS and RADAR. Icarus 270, 222–237 (2016).
Tomasko, M. G. et al. A model of Titan’s aerosols based on measurements made inside the atmosphere. Planet. Space Sci. 56, 669–707 (2008).
Barth, E. L. & Rafkin, S. C. R. TRAMS: a new dynamic cloud model for Titan’s methane clouds. Geophys. Res. Lett. 34, L03203 (2007).
Barth, E. L. & Rafkin, S. C. R. Convective cloud heights as a diagnostic for methane environment on Titan. Icarus 206, 467–484 (2010).
Atkinson, K. R. et al. Penetrometry of granular and moist planetary surface materials: application to the Huygens landing site on Titan. Icarus 210, 843–851 (2010).
Schroeder, S. E., Karkoschka, E. & Lorenz, R. D. Bouncing on Titan: motion of the Huygens probe in the seconds after landing. Planet. Space Sci. 73, 327–340 (2012).
Lorenz, R. D. Wake-induced dust cloud formation following impact of planetary landers. Icarus 101, 165–167 (1993).
Greeley, R. & Iversen, J. D. Wind as a Geological Process on Earth, Mars, Venus, and Titan (Cambridge Univ. Press, Cambridge, 1985).
Shao, Y. P. & Lu, H. A simple expression for wind erosion threshold friction velocity. J. Geophys. Res. Atmos. 105, 22437–22443 (2000).
Claudin, P. & Andreotti, B. A scaling law for aeolian dunes on Mars, Venus, Earth, and for subaqueous ripples. Earth Planet. Sci. Lett. 252, 30–44 (2006).
Kok, J. F., Parteli, E. J. R., Michaels, T. I. & Karam, D. B. The physics of wind-blown sand and dust. Rep. Prog. Phys. 75, 106901 (2012).
Barnes, J. W. et al. Production and global transport of Titan’s sand particles. Planet. Sci. 4, 1 (2015).
Sullivan, R. et al. Wind-driven particle mobility on Mars: insights from Mars Exploration Rover observations at ‘El Dorado’ and surroundings at Gusev Crater. J. Geophys. Res. Planets 113, E06S07 (2008).
Tokano, T. Relevance of fast westerlies at equinox for eastward elongation of Titan’s dunes. Aeolian Res. 2, 113–127 (2010).
Charnay, B. et al. Methane storms as a driver of Titan’s dune orientation. Nature Geosci. 8, 362–366 (2015).
Rafkin, S. C. R. & Barth, E. L. Environmental control of deep convective clouds on Titan: the combined effect of CAPE and wind shear on storm dynamics, morphology, and lifetime. J. Geophys. Res. Planets 120, 739–759 (2015).
Burr, D. M. et al. Higher-than-predicted saltation threshold wind speeds on Titan. Nature 517, 60–63 (2015).
We thank P. Claudin and B. Andreotti for discussions, especially regarding thresholds and modes of sediment transport. We are also grateful to the Cassini/VIMS team for the calibration and planning of the data. We acknowledge financial support from the UnivEarthS LabEx programme of Sorbonne Paris Cité (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02), the French National Research Agency (ANR-APOSTIC-11-BS56-002 and ANR-12-BS05-001-03/EXO-DUNES) and the CNES. This study was partly supported by the Institut Universitaire de France. T.C. was funded by the ESA Research Fellowship Programme in Space Sciences. Part of this work has been performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.
The authors declare no competing interests.
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Rodriguez, S., Le Mouélic, S., Barnes, J.W. et al. Observational evidence for active dust storms on Titan at equinox. Nature Geosci 11, 727–732 (2018). https://doi.org/10.1038/s41561-018-0233-2
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