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Almost a year into its extended mission, Cassini continues to reveal Titan's chaotic, enigmatic surface. On October 15, 1997 NASA launched the Cassini-Huygens spacecraft on a mission to explore Saturn and its family of moons, particularly Titan. It was the largest payload ever sent out to deep space, weighing almost six tons.
It needed most of the seven year journey to Saturn for gravity boosts from Venus, Earth, and Jupiter because it could not carry enough onboard fuel to blast straight out to its target. As it was, the proposed decade-long flight, with engine burns, instrument usage, and radio transmissions to Earth, required that it carry several kilograms of plutonium as its primary power source.
On January 14, 2005 the Huygens probe separated from its mothership and successfully landed on the frigid moon. In June of 2008, the official mission timeline came to an end. It was renamed Cassini Equinox to commemorate the change of seasons on Saturn as the Sun passed through Saturn's equinox and began to illuminate the giant planet from the North. For the four year term of its original mission, Saturn was lit from the South, so NASA engineers are taking advantage of this rare opportunity.
Cassini recently flew close by Titan, and on June 6, 2009 its cameras will once again trace out a swath of radar images as it skims past the planet-sized moon at a distance of 965 kilometers from the surface. It is expected that the same low-lying regions NASA scientists refer to as "lakes," as well as the dendritic channels referred to as "river valleys," will dominate the conversation once the images are analyzed.
For years NASA has maintained that Titan's predominantly methane atmosphere has to be constantly replenished somehow, because so much of it is destroyed by sunlight. If the moon is as old as current theories propose, with that much leakage the atmosphere should have entirely evaporated long ago. The only mechanism that astrophysicists could imagine as a source was oceans of liquid methane beneath the dense cloud cover.
The Huygens lander quickly dispersed that idea when it touched down on what appeared to be a flat, rock-strewn plain. No methane droplets were detected falling from the sky, or precipitation of any kind for that matter, and no pools of methane were seen anywhere within its field of view. Instead, orbital images confirmed a dry surface when vast areas covered with dunes several meters high were seen. The dune fields, along with evidence for deeply carved channels over several hundred square kilometers, demonstrated that forces other than flowing liquids had been at work on Titan.
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