A New World

On January 14, 2005, mankind added another celestial body to the roster of those it had reached out and touched. The Huygens probe, launched from the Cassini mothership 21 days earlier, landed on the surface of Titan and invited it to the very exclusive club which at the time only included the Moon, Mars, and Venus (the comet Tempel 1 was inducted on July 4, 2005).

Titan had long fascinated astronomers with its several unique characteristics. Not only is it one of the largest moons in the solar system, but it is the only satellite with a real atmosphere (not counting the constant haze of volcanic output that surrounds Io). The atmosphere is primarily composed of methane, and murky enough to hide any details of the surface from Earthbound observation.

Since it was difficult to predict what Huygens would encounter when it landed on the planet, it was designed to cope with as many situations as possible. The probe had a tough shell to withstand a touchdown on rocky terrain, and would float if it landed in liquid. The probe was too small to contain a transmitter capable of sending useful amounts of data directly to Earth, so it would relay transmissions through its parent craft. This would also help preserve its 1800 watt-hour power source, which was expected to keep the probe going for 2.5 hours of descent and half an hour of surface activity. Huygens was equipped with a battery of instruments already noded above, ready to examine the inner atmosphere and surface of a truly brand-new world.


The separation, glide, and descent phases of the mission were uneventful- at least in terms of deviation from expectations. The probe was quiescent during most of its lone voyage, while Cassini performed its own remote examination of Titan and moved into position for its role as relay. Upon encountering the outer reaches of Titan's 600km-deep atmosphere, Huygens awoke and established its radio link to Cassini. During the descent, the probe sent back a stream of images of the approaching surface; the probe was rotating as it fell and measured wind behaviors as well as capturing images of rolling clouds, a barren and rocky landscape, and even what appeared to be river channels full of liquid methane. The probe eventually came to rest on gravelly terrain covered with pebbles and dust, on the edge of a large, dark region it had seen on the way down, and returned close-up images of the surface and measurements of the properties of the low-level atmosphere.


The knowledge gained from the Huygens mission was enhanced by two extremely fortunate events. Firstly, the probe's power source, predicted to last for half an hour after touchdown, was able to hold out for over twice that long- one hour and 12 minutes. Secondly, an error in communications between Cassini and Huygens resulted in the loss of data from the probe's Doppler Wind Experiment- but a team on Earth, following the probe through telescopes, were able to make equivalent measurements from the observed movement of the probe and salvage the DWE team's project.

After Cassini-Huygens, the future looks bright for exploration of the outer solar system. NASA is moving ahead on its Project Prometheus mission, a return to the gas giants and a testbed for future nuclear-powered spacecraft. They are also ready to collaborate with the ESA again on a mission to the surface of Europa (go ahead and say it; I'll wait), now that it's been proven that moons can be just as interesting, and withhold just as many secrets, as the planets themselves.