Apparently it is a wonderful day for astronomical news. Who knew? I'm one of those people who loves to read about astronomy (particularly planetary science) but never actually goes outside and looks up. Anyway, this next story I found in a couple of places and thought it was pretty interesting.
So lets take a look at a particular paradox that exhists on Titan. What we know about the rotation of planetary atmospheres plus data from the Huygens probe (which landed on Titan's surface) tells us that surface winds should go east to west. Then the Cassini spacecraft sent images of Titan's equatorial dunes which suggested that the winds were moving west to east. A new paper in Aeolian Research, and a related paper in Science, attempt to explain this phenomenon.
These papers propose that there are seasonal changes on Titan that reverse the wind patterns for a short period. The equinoxes appear to be particuarly important. Now it is easy to start thinking of other planets like you think of your own, but Saturn is a large planet to orbit around and it is very far away from the sun. One year on Titan is about 29 Earth years, and during that time the moon will have two equinoxes. These are times when the heat from the sun creates atmospheric upwellings, causing the winds to reverse and accelerate (kinda like monsoons on Earth). Short gusts of west-to-east winds occurring intermittently over two years are so strong that they transport the dunes' sand more effectively than the normal east-to-west winds, causing these reverse striations in the dunes.
Take a look through the articles:
Tokano, Tetsuya. (2010) Relevance of fast westerlies at equinox for the eastward elongation of Titan's dunes. Aeolian Research: In press. (DOI: 10.1016/j.aeolia.2010.04.003)
Lorenz, Ralph D. (2010) Winds of Change on Titan. Science: 329(5991), 519 - 520. (DOI: 10.1126/science.1192840)
(image credit: NASA/JPL)