SSS 2009-12-24（在线收听）

The northeast just had its first big snow of the season. Meanwhile, on Titan, it was foggy. That weather report brought to you by researchers publishing in the journal Astrophysical Journal Letters. The scientists found that Titan, Saturn’s largest moon, is covered with puddles of liquid methane, which give rise to a fog that’s as thick as pea soup—and smells a whole lot worse.

To make fog, you need lots of liquid. Here on earth, we use water. We’ve got water on the ground and in the air. And when the air can’t hold any more moisture because it’s totally saturated or it cools down, you get condensation. So the morning fog, and the dew on your windshield, comes from air that’s cooled enough that it can’t hang onto its water.

Titan fog, on the other hand, comes from methane. Like water, methane can be a solid, liquid, or gas. On Titan, methane forms clouds and maybe even rain. And, when atmospheric methane condenses, it makes fog. That fog then sticks around because it’s in contact with the methane puddles, which keeps everything cool enough to keep the methane condensing.

So next time you visit Titan, don’t expect to get any great pictures of Saturn. And drive with your low beams on.