As the Huygens probe prepared to plunge into the atmosphere of Titan, the scientists at the European Space Operations Center in Darmstadt, Germany, kept warning the packed auditorium full of colleagues and journalists to “expect the unexpected.” Saturn’s planet-size moon is completely enshrouded in an orange-brown haze. It is 10 times as far from the sun as Earth is, its thick atmosphere is tinged with methane (the air would burst into flame if oxygen were present), and it has about a seventh of Earth’s surface gravity. Whatever lay under Titan’s global smog would surely boggle the imagination.
On the evening of January 14, when the snapshots from Huygens started to arrive, the researchers were startled anyway. The first set of images showed formations resembling riverbeds, eroded hillsides, coastlines, sandbars, and barrier islands that made Titan look improbably like Earth. One early Huygens picture looked eerily like the New Jersey shore. “Nah, it’s too rugged,” said Martin Tomasko of the University of Arizona, lead researcher on Huygens’s camera-spectrometer package, eyeballing a pile of color printouts scattered on a table in front of him. “It’s more like the south of France.”
At second look, however, nothing on Titan is quite what it seems. The thermometer hovers around –290 degrees Fahrenheit—cold enough to provoke chemistries and states of matter never seen naturally on Earth. The hills on Titan are rock-hard frozen water. The rain is condensed methane. The dark deposits in the channels and lowlands are most likely a tar that precipitated out of the hydrocarbon-rich atmosphere.
Titan’s contrast of the recognizable and the bizarre carries a profound lesson. If we ever see Earth-like worlds around other stars, there’s a good chance they will seem familiar too. All it takes is air, fluid, and a little geologic activity to create a place that looks remarkably like home. Titan expands our perspective on the whole range of landscapes out there.
