Summary: The Sahara Desert is one of the driest regions on Earth. Even so, small oases dot the landscape — regions where water bubbles up from below the surface to fill ponds or small lakes. An oasis may also highlight the “desert” regions of Titan, the largest moon of Saturn. But this oasis is as big as Utah’s Great Salt Lake. Titan is blanketed by a cold, dense atmosphere. A layer of orange haze tops the atmosphere, so we can’t see Titan’s surface directly. But the Cassini spacecraft has used radar to peer through the haze and map a large fraction of the surface. Those observations have revealed hundreds of possible lakes close to the moon’s poles. Titan is so cold, though, that water at the surface is frozen as hard as granite. So instead, the lakes are filled with liquid methane and ethane. Planetary scientists recently reported the discovery of a big lake at Titan’s equator, too. Models of Titan’s atmosphere suggest that any liquid in that region would quickly evaporate and be carried toward the poles, so the equator should stay dry. The lake may be fed by springs. If so, then the discovery may help solve a puzzle. Titan’s atmosphere contains a lot of methane. But methane is quickly destroyed by solar energy. That means there must be a source of fresh methane to replenish the atmosphere. And underground springs would be a good source — helping fill not only desert oases, but the lakes at higher latitudes as well. More about Titan 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.
