The Cassini probe had previously (about 10 years ago) found 300 foot-high sand dunes on Titan, but there were many mysteries about those dunes.
Scientists were not sure what was the source of the grains, nor how the winds could be strong enough to form the dunes, nor why the narrow shape of
the dunes seem to indicate that they were formed by winds moving the opposite direct that winds are believed to be moving on Titan (the dunes looked
to be laid out by westerly winds, while the winds on Titan blow easterly. They now think they have ideas about some (but not all) of the mysteries of
Cassini radar sees sand dunes on Saturn's giant moon Titan (upper photo) that are sculpted like
Namibian sand dunes on Earth (lower photo). The bright features in the upper radar photo are not clouds but topographic features among the dunes.
Apparently, sand dunes are not that common in the solar system, which makes sense when you think about it, because there would need to be (1) solid
materials to blow around and (2) Atmosphere and winds to do the blowing.
Sand dunes have been found in just a few places throughout the solar system - on Venus, Mars, Earth and Titan - but Titan is the only moon where
dunes have been discovered.
Also, it is believed that the sand isn't made up of silicates, but hydrocarbons and ice.
The sand that makes up Titan's dunes is not made of silicates like the sands we find on Earth, however. Instead, scientists believe it is made of
hydrocarbons, and may include particles of water ice.
Titan is so cold that water ice there is as hard as rock. In fact, in the image below taken from the Huygens probe that landed on Titan (the only
probe to ever see the surface up close), the visible rocks and boulders are thought to be boulders of water ice with a hydrocarbon coating.
While what the source of the grains are is still a mystery, but by modeling the conditions on Titan in a wind tunnel, scientists have discovered
possible explanations about the speed of the winds required, and about the peculiar layout of the dunes. It turns out that scientist now think that
the wind speeds need to be 50% faster
than they previously thought they needed to be in order to move the sand. Their explanation for
mystery of the wrong-way dunes also may help explain the higher than predicted winds.
Scientists found that there may be times that the winds on Titan shift direction from easterly to westerly. This happens twice during a Saturn year,
which is 30 Earth-years, and during those times, the wind also moves faster -- fast enough (only then) to move the sand.
According to atmospheric models, the wind reverses twice during a Saturn year which is equal to about 30 Earth years. This reversal happens when
the sun crosses over the equator, causing the atmosphere -- and subsequently the winds -- to shift. Burr theorizes that it is only during this brief
time of fast winds blowing from the west that the dunes are shaped.
"The high wind speed might have gone undetected by Cassini because it happens so infrequently."
Titan's 300-foot-high sand dunes were formed by
Saturn's largest moon is a windy place: Titan dune puzzle solved
edit on 12/9/2014 by Soylent Green Is People because: (no reason given)