Huygens Touches Titan: Saturn's Moon Revealed

After a seven-year journey covering 2.2 billion miles, the Huygens probe detached from the Cassini orbiter and plunged into the orange haze of Titan's atmosphere on January 14, 2005, becoming the first human-made object to land on a world in the outer solar system. For seventy-two minutes during its descent and another hour and twelve minutes on the surface, Huygens transmitted data that revealed Saturn's largest moon to be one of the most Earth-like bodies ever explored. Titan had fascinated planetary scientists since the 1940s, when Dutch-American astronomer Gerard Kuiper detected methane in its atmosphere, the only moon in the solar system known to have a substantial one. The Voyager 1 flyby in 1980 revealed that the atmosphere was denser than Earth's, composed primarily of nitrogen with methane and other hydrocarbons, but the thick orange smog prevented any view of the surface. What lay beneath the haze became one of the solar system's great mysteries. Huygens answered that question with 350 photographs taken during its two-and-a-half-hour parachute descent. The images showed a landscape of rolling hills, drainage channels carved by liquid methane, and a shoreline where a dark plain met brighter highlands. The surface itself, when Huygens touched down at approximately 12 miles per hour, was a frozen mudflat of water ice and hydrocarbon sediment with the consistency of wet sand. An onboard microphone recorded the sound of alien wind. The probe's instruments measured surface temperature at minus 292 degrees Fahrenheit and atmospheric pressure at roughly 1.5 times that of Earth's sea level. A gas chromatograph detected traces of cyanogen and other complex organic molecules in the atmosphere. The data confirmed that Titan has a methane cycle analogous to Earth's water cycle, with methane rain, methane rivers, and methane lakes. Huygens was built by the European Space Agency and named after Christiaan Huygens, the seventeenth-century Dutch astronomer who discovered Titan in 1655. The probe's batteries lasted far longer than expected, and its final transmission came 72 minutes after landing, when Cassini moved out of radio range. Those few hours of data from the surface of a world 890 million miles away remain among the most remarkable achievements in the history of space exploration.