Astronomers Disagree About Iapetus Oddities |
| Written by spacetravel.org | |||
| Thursday, 12 May 2005 21:46 | |||
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Paulo Freire, of the Arecibo Observatory in Puerto Rico, thinks that both features were formed when the moon collided with the edge of one of Saturns rings a long time ago. Debris from the ring smashed into a narrow region along Iapetus equator, piling up to create the ridge. The fact that the ridge does not extend over the entire hemisphere is consistent with Freires claim that Iapetus only grazed the ring. Freire argues that the energy from the impact evaporated the icy parts of the rings debris, producing a local atmosphere that consisted mostly of water vapor. Because Iapetus did not have any other atmosphere, the water vapor rapidly spread toward the north and south poles, creating a temporary wind that deposited debris over the moons leading face. This created the dark side. This idea is supported by the fact that the dark coating appears to get thinner the closer it gets to the poles. However, Larry Esposito, a specialist on planetary rings at the University of Colorado in Boulder, says that Freires theory is flawed because today Iapetus orbit is far outside of Saturns rings and not even in the same plane as the rings. This makes it unlikely that Iapetus ever collided with a ring. Freire suggests that Iapetus may initially have been closer to Saturn than it is now, but somehow migrated into a higher orbit, possibly because of an encounter with another moon. Carolyn Porco, leader of the Cassini spacecrafts imaging team at the Space Science Institute in Boulder, Colorado, thinks Iapetus ridge is a tectonic feature. She believes the dark coating may have been caused by the moon passing through a dark cloud of cometary debris. Cassinis next and final encounter with Iapetus, which is scheduled for September 10, 2007, may provide some answers.
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