Exactly ten years ago, the Huygens space probe landed on the surface of Saturn’s moon Titan. It is the only probe to have successfully landed on an outer solar system object. Titan was a great choice, because it is the only moon in the solar system with a notable atmosphere. It’s surface pressure is about 40% greater than the Earth’s. And it’s atmosphere is made up mostly of nitrogen. Now you may wonder why all that nitrogen doesn’t just escape off into space. It is because it doesn’t have enough energy. Titan might not have much gravitational pull, but its surface temperature is 94 K — roughly -290 °F. Still, overall, it is a lot like the Earth with wind, rain, and seas. It is just that instead of water, Titan has liquids of simple hydrocarbons like methane and ethane.
In 1997, the European Space Agency launched Cassini—Huygens. It was an incredibly ambitious mission, flying by many planets and moons before going into orbit around Saturn in 2004. On 25 December 2004, Cassini released the Huygens probe, which reached Titan’s atmosphere on 14 January 2005. It descended to the surface two and a half hours later. Not a great deal was known about Titan until this mission, because (like with Venus), it’s think atmosphere obscured its surface details. In fact, it was long thought that Titan was the largest moon in the solar system, because its large atmosphere was counted as part of the solid moon.
One of the most interesting things about Titan is how much water it has. It’s density is less than double the density of water — and about half the density of the moon and one-third that of the Earth. On the surface are “rocks” of frozen water. But amazingly, Titan appears to have a thick subsurface layer of liquid water. Overall, it is about the most fascinating object in our solar system — other than the Earth itself.
After about an hour and a half on the surface of Titan, Huygens ran out of battery power and now just sits there on Titan. It is interesting to think, however, that it seems to have landed in a dry flood plane. So by now, it might have been carried off somewhere else. Titan really is very Earth like. So you can imagine what might happen to a similar probe that was just abandoned in the Mississippi delta.