Wednesday, December 29, 2004
Titan pole flattening
One of the latest postings on the Cassini-Huygens web site is this: http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1256. What causes the apparent flattening of the moon? Jupiter and Saturn have flattened globes, and noticeably so even in a backyard telescope. Saturn's polar diameter, in fact, is about 8000 miles less than through the equator, about 10%. These large planets have extremely rapid rotation rates; their "days" are about ten to eleven hours. Couple this with extremely deep atmospheres, and we get a mathematical model which favors pole flattening.
Titan can have no such explanation; the assumption is that Saturn's gravity has tidally locked the rotation to correspond to the moon's orbit of the planet. Titan spins far more slowly than the giant planets rotate on their axes. I also think earth-based radar scans of Titan's surface have confirmed this. But I wonder if the atmosphere is affected by Saturn's gravity in the form of tides? Unlike the dual effect of moon and sun on the earth's oceans, Titan would have a bulge of gas and surface liquid always along an axis pointing toward the planet. The other nearby moons might also have an effect. The only way to confirm Saturn tides on Titan's atmosphere would be to image the moon from different Saturn-Titan perspectives. If Cassini were 90 degrees from Saturn from Titan's perspective, tidal flattening would be optimal. If Cassini imaged the moon while passing in front of Saturn, then tidal flattening would be less. I imagine there's mathematics that would predict tides, but that's beyond my ability.
