Probe Set to Enter Titan's Atmosphere

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"I've sat in a couple of meetings that had the majority of the world's experts on Titan sitting together, and for the first time they've been suspiciously quiet," he said.

Showing light and dark patches, the images lack any sign of impact craters. In Zarnecki's opinion, the missing craters stand out as the most telling feature. He believes geologic activity or weathering erased them.

"Every surface [in] the solar system is pockmarked with [impact] features except for those that are active in some way," he said.

Information gathered during Cassini's recent flybys of Titan has confirmed scientific models of the moon's atmosphere, according to Lebreton. The finding has bolstered the confidence of the space mission's project scientists that Huygens will enter safely, he said.

Titan Encounter

During the descent from Cassini all systems were shut down, except for three timers designed to wake up the probe four hours before its landing on January 14.

Upon arrival, the probe will be traveling at about four miles a second (six kilometers a second). It will deploy a series of parachutes and open a communications link with Cassini to relay images and scientific data to Earth.

If all goes according to plan, the probe will drift through the atmosphere for about two and a half hours before it reaches the surface, sending scientists more than a thousand images and details about the lunar atmosphere's structure, composition, and winds.

Huygens, which is designed primarily as an atmospheric probe, is expected to land about 10 degrees south of Titan's equator and several hundred kilometers west of a bright landmark known as Xanadu. Some scientists speculate the feature is a giant icy mountain.

But precisely what the probe will land in or on—rock-hard ice, a sea of gungy methane, or something else—remains an open question. The probe's atmospheric entry point was selected to capture the best images during descent. The landing surface was irrelevant to mission planners.

"The probe may drift by several hundred kilometers in the winds during descent, so there was no way, and no reason, to target a specific patch on the surface," Lebreton said.

If the probe survives touchdown, it will have no more than two hours to relay images and data about Titan's surface before Cassini drifts over the horizon, severing the communications link.

"If we got two hours worth of data on the surface that would be beyond my wildest dreams, that would be truly wonderful," Zarnecki said.

Cassini will continue to make observations of Titan on more than 40 subsequent flybys during the spacecraft's mission.

"Titan is really a fascinating body to explore and its surface a big puzzle," Lebreton said. "It will take all the synergy between the repeated Cassini orbiter observations and the detailed [direct] observation of Huygens to put all the pieces of the puzzle together."

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