When NASA’s Cassini spacecraft took off towards Saturn, it brought along a passenger: the ESA’s Huygens probe, which is designed study Saturn’s largest moon, Titan. The two spacecraft have been orbiting together for a few months now, but on January 14, 2005, Huygens will make the plunge into Titan’s thick methane and hydrocarbon atmosphere. And if it’s really lucky, the probe will survive the journey down to the moon’s surface, and give scientists a unique opportunity to study an environment that might have been similar to our own Earth’s early history.