Dust Storms on Titan Spotted for the First Time

Artist’s concept of a dust storm on Titan. (Credits: IPGP/Labex UnivEarthS/ University Paris Diderot – C. Epitalon & S. Rodriguez)
PARIS (NASA PR) — Data from NASA’s Cassini spacecraft has revealed what appear to be giant dust storms in equatorial regions of Saturn’s moon Titan. The discovery, described in a paper published on Sept. 24 in Nature Geoscience, makes Titan the third Solar System body, in addition to Earth and Mars, where dust storms have been observed.

The observation is helping scientists to better understand the fascinating and dynamic environment of Saturn’s largest moon.

“Titan is a very active moon,” said Sebastien Rodriguez, an astronomer at the Université Paris Diderot, France, and the paper’s lead author. “We already know that about its geology and exotic hydrocarbon cycle. Now we can add another analogy with Earth and Mars: the active dust cycle, in which organic dust can be raised from large dune fields around Titan’s equator.”

Titan is an intriguing world — in ways quite similar to Earth. In fact, it is the only moon in the Solar System with a substantial atmosphere and the only celestial body other than our planet where stable bodies of surface liquid are known to still exist.

There is one big difference, though: On Earth such rivers, lakes and seas are filled with water, while on Titan it is primarily methane and ethane that flows through these liquid reservoirs. In this unique cycle, the hydrocarbon molecules evaporate, condense into clouds and rain back onto the ground.

The weather on Titan varies from season to season as well, just as it does on Earth. In particular, around the equinox — the time when the Sun crosses Titan’s equator — massive clouds can form in tropical regions and cause powerful methane storms. Cassini observed such storms during several of its Titan flybys.

This compilation of images from nine Cassini flybys of Titan in 2009 and 2010 captures three instances when clear bright spots suddenly appeared in images taken by the spacecraft’s Visual and Infrared Mapping Spectrometer. (Credits: NASA/JPL-Caltech/University of Arizona/ University Paris Diderot/IPGP/S. Rodriguez et al. 2018)

When Rodriguez and his team first spotted three unusual equatorial brightenings in infrared images taken by Cassini around the moon’s 2009 northern equinox, they thought they might be the same kind of methane clouds; however, an investigation revealed they were something completely different.

“From what we know about cloud formation on Titan, we can say that such methane clouds in this area and in this time of the year are not physically possible,” said Rodriguez. “The convective methane clouds that can develop in this area and during this period of time would contain huge droplets and must be at a very high altitude — much higher than the 6 miles (10 kilometers) that modeling tells us the new features are located.”

The researchers were also able to rule out that the features were actually on the surface of Titan in the form of frozen methane rain or icy lavas. Such surface spots would have a different chemical signature and would remain visible for much longer than the bright features in this study, which were visible for only 11 hours to five weeks.

In addition, modeling showed that the features must be atmospheric but still close to the surface — most likely forming a very thin layer of tiny solid organic particles. Since they were located right over the dune fields around Titan’s equator, the only remaining explanation was that the spots were actually clouds of dust raised from the dunes.

Organic dust is formed when organic molecules, formed from the interaction of sunlight with methane, grow large enough to fall to the surface. Rodriguez said that while this is the first-ever observation of a dust storm on Titan, the finding is not surprising.

“We believe that the Huygens Probe, which landed on the surface of Titan in January 2005, raised a small amount of organic dust upon arrival due to its powerful aerodynamic wake,” said Rodriguez. “But what we spotted here with Cassini is at a much larger scale. The near-surface wind speeds required to raise such an amount of dust as we see in these dust storms would have to be very strong — about five times as strong as the average wind speeds estimated by the Huygens measurements near the surface and with climate models.”

The existence of such strong winds generating massive dust storms implies that the underlying sand can be set in motion, too, and that the giant dunes covering Titan’s equatorial regions are still active and continually changing.

The winds could be transporting the dust raised from the dunes across large distances, contributing to the global cycle of organic dust on Titan and causing similar effects to those that can be observed on Earth and Mars.

The results were obtained with Cassini’s Visual and Infrared Mapping Spectrometer. The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the mission for NASA’s Science Mission Directorate in Washington. The Cassini spacecraft deliberately plunged into Saturn on Sept. 15, 2017. JPL designed, developed and assembled the Cassini orbiter. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the U.S. and several European countries.

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  • Robert G. Oler

    the most “earth like” place in teh solar system 🙂

  • Andrew Tubbiolo

    Yeah it’s Earth like, it’s like a oil refinery on Earth :).

  • ThomasLMatula

    Shouldn’t be surprising. If a world has an atmosphere and there is no vegetation, regional and global dust storms should be expected. How they impact exploration will be a function of the density of the atmosphere and the strength of the electrical discharges that will accompany them from the dust blowing around.

  • Robert G. Oler

    its got the correct gravity, pressure and a boat load of “raw materials” one could function there without a pressure suit…its way out of our reach “now” but someday

  • Robert G. Oler

    if Mars was like Alaska, or even the south pole…even if you had to have O2 to breath…we would be there and make some place out of it…its not

  • Andrew Tubbiolo

    Titan is a special place and when we have fusion power plants that only weigh in at a few tons we’ll go there with people. For all the special qualities that Titan has on it’s surface what planetary scientists theorize lies below is just as interesting. There’s a sub Titanian ocean of water down below that very special surface and atmosphere. At least some have reason to think so. If so, what special world that bridges the cryosphere with the water zone of the solar system. Titan is a very special world.

  • ThomasLMatula

    Yes, wouldn’t it be great to have a station in orbit over it with researchers running rovers and submarines on it?

  • Robert G. Oler

    exactly…it is in my view the key to the outer solar system…but we have to have an inner solar system economy to get there 🙂

  • Robert G. Oler

    or better yet on it

  • Michael Vaicaitis

    what do you mean by “correct gravity”?

    “function there without a pressure suit”
    At -180 C, it would be like “functioning” inside a BFR methane fuel tank

  • Robert G. Oler

    I dont mean to conflate it with earth like, but my guess would be that it would be far easier then functioning in a 6 or so PSID pressure suit. you would need slight positive pressure I would assume and total air tight integrity…as well as protection from the cold…and an O2 environment

    but without the massive pressure part, which is what makes EVA and lunar/mars ops very difficult.

    we are wow at best 50-75 years from that and that assumes that well things start moving at some point

  • Michael Vaicaitis

    I suspect the perpetual extremely cold temperature on Titan would be a bigger obstacle than the lack of pressure combined with relatively benign daytime temperatures on Mars. Particularly if mechanical counter-pressure spacesuits (recall Dava Newman) come to fruition.

  • Andrew Tubbiolo

    That will happen. It’ll be 100+ years probably, but it will happen.