There are only two worlds in the solar system where rain falls on a solid surface, carving riverbeds and filling broad, dark lakes. One of them is Earth. The other is Titan, the largest moon of Saturn. But there’s one big difference between them: temperature. Titan is more than 300 degrees colder than Earth is, so the liquid that falls from its skies and fills its lakes is not water, but methane.
Titan is the second-largest moon in all the solar system — about as big as the planet Mercury. But it ranks second to none in the “intriguing” category.
For one thing, it’s the only moon with a thick atmosphere — more than half again as thick as Earth’s. And like Earth, the atmosphere supports a cycle of rainfall and evaporation. It’s not yet clear whether the rainfall takes the form of a steady drizzle or periodic showers.
The rains fill lakes near Titan’s poles, but just how that works is also unclear. It could be that the lakes remain at least partially full year-round, and the rains just top them off. Or a more likely scenario is that the lakes dry up during summertime and refill during winter.
Perhaps most intriguing of all, Titan contains many of the organic building blocks for life — not just methane, but many of the other compounds from which life arose here on Earth. So Titan may well be a chilly version of a very early Earth — a world with all the ingredients for life.
We’ll have more about Titan tomorrow.
Script by Damond Benningfield, Copyright 2012
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