for National Geographic News
Twenty days after being jettisoned by its mothership, the Huygens space probe plunged through the hazy atmosphere of Titan early Friday morning and landed on the Saturn moon.
Huygens has since sent dozens of images back to Earth (see the first color image from Huygens alongside this article), revealing the first glimpses of the moon's surface. The images show an Earthlike surface strewn with what are thought to be blocks of ice.
Images made by the probe during its parachute descent through Titan's atmosphere reveal what scientists say looks like a shoreline and drainage channels, perhaps for liquid methane. Titan is much too cold for water to exist in liquid form.
Scientists hope the data could help unlock the mystery of Saturn's biggest moon and yield answers to fundamental questions about chemistry and physics, planetary formation, and the conditions that gave rise to life on Earth.
As the second largest moon in our solar system, Titan has long intrigued scientists. Its atmosphere and surface composition are thought to resemble those of the Earth at the time of our planet's formation.
"Titan is sitting up there perking away as kind of a planet-scale chemistry lab doing a lot of the stuff that was going on in the Earth's atmosphere four billion years ago," said Torrence Johnson, a research scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. Johnson is a member of the imaging-science team on the Cassini spacecraft.
Launched in 1997, the Cassini-Huygens mission is jointly managed by NASA, the European Space Agency, and the Italian Space Agency. It arrived in Saturn's orbit on July 1, 2004, for a four-year mission to study the planet, its rings, and moons.
Saturn is the second largest planet in our solar system, after Jupiter. It is composed mostly of hydrogen and helium gas, making it the least-dense planet in our solar system. It has 31 known moons, 13 of which were discovered after Cassini was launched.
Huygens, which has spent the last seven years bolted to Cassini, was jettisoned by the spacecraft on Christmas Day. For 20 days the clam-shaped, 8.9-foot-wide (2.7-meter-wide), 703-pound (319-kilogram) probe has been plummeting toward Titan.
During its descent, all systems were shut down, except for three timers designed to wake up the probe four hours before its landing.
On arrival, the probe was expected to travel at about four miles a second (six kilometers a second). Huygens was designed to deploy a series of parachutes and open a communications link with Cassini to relay images and scientific data to Earth.
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