- Before the Cassini/Huygens mission, Titan was a cipher—the largest expanse of unglimpsed terrain left in the solar system, larger than the planet Mercury.
- Having penetrated the haze with infrared images, radar and a descent probe, the mission has discovered a dynamic landscape of rivers, lakes, dunes, mountains and possibly volcanoes. It is a frigid version of Earth, where methane substitutes for water, water substitutes for rock, and weather cycles last centuries.
- Studying Titan is already elucidating the geologic processes of our own planet, such as dune formation and climate change.
If we had not known the images were coming back from Titan, we might have guessed they were new pictures of Mars or Earth. Some people in the control room saw the California coast, some saw the French Riviera, and one person even said that Saturn’s biggest moon looked like his backyard in Tucson. For three weeks, the Huygens probe had coasted, dormant, after detaching from the Cassini spacecraft and being sent on its way to Titan. Those of us watching anxiously felt a deep personal connection with the probe. Not only had we worked on the mission for a large part of our careers, but we had developed its systems and instrumentation by putting our minds in its place, to think through how it would function on an alien and largely unknown world. We imagined Titan might be like the comparably large moons of the outer solar system, such as Jupiter’s cratered Callisto or grooved Ganymede.
And so on the morning of January 14, 2005, at the European Space Operations Center in Darmstadt, Germany, the pictures caused jubilation and puzzlement in equal measure. None of us expected the landscape to look so Earth-like. As Huygens parachuted down, its aerial pictures showed branching river channels cut by rain-fed streams. It landed on the damp, pebble-covered site of a recent flash flood. What was alien about Titan was its eerie familiarity.
This article was originally published with the title The Moon That Would Be a Planet.