Future missions to Saturn's moon Titan may have to contend with blowing particles and higher-than-expected winds from recently discovered dust storms.

Illustration of proposed Titan lander
Proposed Titan missions, such as the Dragonfly lander illustrated here, will have to contend with dust storms on the moon.

Saturn’s moon Titan is known to have an atmosphere and a liquid cycle, just like Earth. A new finding shows that the little world also has dust storms, making it a potentially tricky place for future landers.

Titan already has hosted one lander, called Huygens. It arrived in 2005 for an hours-long mission in which it collected data and pictures while descending to the surface. Huygens made a single direct wind speed measurement of less than 1 meter per second (about 2 mph), according to the European Space Agency. New data found from partner spacecraft Cassini, however, show dust kicked up from winds that were likely five times as strong.

"In 2009, near Titan’s northern spring equinox, the Cassini spacecraft observed three distinctive and short-lived spectral brightenings close to the equator, with a very unusual infrared color," said lead author Sébastien Rodriguez (Paris Diderot University) in an e-mail to Sky & Telescope.

Further simulations suggested the brightenings are consistent with large dust storms made up of micron-sized solid organic particles, originating from dune fields on the moon's surface. Methane clouds were also considered as a hypothesis, but the study authors concluded the clouds are too thin and low in altitude to produce the brightening Cassini observed.

A paper based on Rodriguez's work was published September 24th in Nature Geoscience.

Titan's dust storms are distinct from Mars, where regional disturbances occasionally evolve into planet-wide storms for reasons scientists still poorly understand. NASA's solar-powered Opportunity rover is a possible victim of the last global Martian dust storm that kicked up in June 2018; no one has heard from it for months. On Titan, it's still not clear if the same dust is present throughout the planet, or if the conditions for dust lifting are met everywhere. Rodriguez suspects, however, that these storms would be confined to the dryer equator, where most of the large dune fields are located.

The more worrying aspect for spacecraft on Titan may be the winds, Rodriguez said, especially because Titan has an atmospheric density seven times greater than Earth's. “Shear stress on mechanical parts and turbulence problems in flight” might create issues for a probe, he said.

Picture of collapsible ball-like robot
This collapsible, lightweight structure is one of many concepts being explored for missions to places such as Titan.

Adrian Agogino (NASA Ames Research Center) once received funding from the early-stage NASA Innovative Advanced Concepts (NIAC) program for a ball-like, hollow, expandable rover that would roam the surface. He says the new findings reinforce the utility of his concept over a traditional Mars-like rover, due to the changing sandy environment. "People don't like dust, and rovers don't like dust," he says. Yet traction could be a problem even for his vehicle concept, he acknowledges, given the stronger-than-expected winds.

Fellow NIAC recipient Larry Matthies (NASA Jet Propulsion Laboratory) received funding for an aerial vehicle for Titan. Ideally, he says, future Titan spacecraft could gather information on dust storm probability, the magnitude of the winds, and the effect on visibility. At the moment, the data available are sparse; figuring out how to re-engineer Titan aircraft or landers "is in the realm of speculation right now," he concludes.

More data could even come from Cassini. While the spacecraft concluded its work last year, Rodriguez said the logical next step is to search more of Cassini's data to find information on dust storm timing, location, and properties. Scientists could also run new climate models of Titan based on what is known about the dust storms. The ultimate goal, he said, is to better predict what causes dust storms based on local climatic conditions, such as humidity and wind.




Image of Roger Venable

Roger Venable

October 9, 2018 at 8:33 am

Nice article. Just one point of information:
Titan's atmosphere is about 1.5 times as dense as Earth's, not 7 times denser. The confusion may arise from the fact that the _mass_ (not the density) of Titan's atmosphere above each square foot of Titan's surface is about 7 times as great as the mass of Earth's atmosphere above each square foot of Earth. However, Titan's lower gravity limits the density to 1.5 times as great. With regard to the movement of dust, it is the density that is relevant, not the mass, so the factor of 1.5x is the important one.
-- Roger Venable

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