Summary: When the Voyager 1 spacecraft arrived at Saturn in 1980, scientists were almost as eager to see Saturn’s largest moon as they were the planet itself. Observations from the ground had detected an atmosphere. But Titan is so small and far away that no one could learn much about it, or see how it affected the surface below. It turned out that Voyager couldn’t see the surface, either, because the atmosphere is topped by a thick haze. So all the craft saw was a featureless orange ball. But its instruments did reveal that Titan’s atmosphere is thicker than Earth’s, and that it consists mainly of nitrogen — the main ingredient in Earth’s atmosphere as well. Voyager also detected a mixture of hydrocarbons in the air, such as methane and ethane. And it measured a surface temperature of about 300 below zero Fahrenheit. Planetary scientists soon speculated that methane and ethane could fill an ocean that would cover Titan’s entire surface. But 15 years after Voyager, Hubble Space Telescope peered through the haze to provide a rough look at the surface, and it found no evidence of an ocean. But we didn’t get a really good look at Titan until Cassini entered orbit around Saturn in 2004. It used radar and other instruments to see the surface. Its observations have revealed lakes of liquid methane and ethane, riverbeds, and giant sand dunes. These features keep Titan’s surface young — and we’ll talk more about that tomorrow. Script by Damond Benningfield, Copyright 2012 This program was made possible in part by a grant from the NASA Science Mission Directorate. For more skywatching tips, astronomy news, and much more, read StarDate magazine.
