Giant dust storms have been observed in the equatorial regions of Saturn's moon Titan for the first time.
The storm was observed by NASA's Cassini probe, the first space craft to enter the orbit of Saturn, and reflected in data sent back by the craft before it was destroyed in Saturn's upper atmosphere.
The discovery means that Titan is only the third Solar System body, in addition to Earth and Mars, where dust storms have been observed.
NASA said the observation will help scientists better understand the 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 lead author of the research, which has been published in the journal Nature Geoscience.
"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, which has a surface temperature of around -180 degrees celsius, is the only moon in the solar system with some similarities to Earth. It's also the only moon in the orbit of Saturn with a substantial atmosphere, and the only celestial body other than our planet where stable bodies of surface liquid are known to still exist. It also has seasons.
The big difference, however, is that on Earth we have rivers, lakes and seas filled with water, but 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 important thing to note is that around the equinox - the time when the Sun crosses Titan's equator - massive clouds can form in tropical regions and cause powerful methane dust storms.
The Cassini spacecraft observed such storms during several of its Titan flybys.
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. But a new investigation has 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 that modelling tells us the new features are located."
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.
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