For the past two weeks, space scientists in Europe and the United States have divided their time between celebrating and feverishly studying new data. On January 14, astronomers at the operation center for the European Space Agency (ESA), in Darmstadt, Germany, greeted the end of a long journey with cheers. After a seven-year 2.2 billion-mile trip through the solar system, the ESA's Huygens (hoy-gunz) probe descended through the atmosphere of Saturn's largest moon, Titan, and landed on its surface. "This is a great achievement," said Jean-Jacques Dordain, the director general of the ESA.
The 700-pound saucer-shaped Huygens probe is part of an international joint project between the ESA, NASA and Italy's space agency. The probe rode piggyback on the U.S.-built Cassini spacecraft. Cassini-Huygens was launched in 1997. On its to-do list: explore Saturn, its rings and several of its moons, including Titan.
Last June, the spacecraft entered the ringed planet's orbit and began sending information back to Earth. On Christmas Eve, the probe separated from Cassini and began a 2.5 million-mile voyage to its close encounter with Titan. The moon is one of the largest in the solar system, even larger than the planets Mercury and Pluto. Scientists believe that Titan's atmosphere is similar to that of early Earth. Titan could provide clues to how life began on Earth 4.5 billion years ago.
A Bumpy Ride--Then Splat
After traveling for 20 days, the probe entered Titan's atmosphere and
streaked to the surface at a rate of about 11,000 miles per hour. Strong
winds seemed to have rocked the probe as it dropped. "The ride was
bumpier than we thought it would be," said Martin Tomasko, a Huygens
scientist.
After Huygens's parachutes unfurled, the probe slowed and touched down with a splat! Data suggests that the probe set down on mud or wet clay covered by a thin, frozen crust. All through its descent and for at least 70 minutes afterward, the probe's instruments measured Titan's temperature, gravitational pressure, wind speed and atmosphere. Huygens sent data to the orbiting Cassini spacecraft, which then relayed it to telescopes on Earth.
Huygens sent more than 350 pictures. They depicted a landscape and weather systems that are extraordinarily like those on Earth but that use different chemistry. Some images showed what appeared to be a network of drainage channels, river systems, lake beds and islands. Instead of water, astronomers think this land could hold liquid methane. There's also evidence that Titan has experienced volcanic activity. But instead of lava, scientists think the moon's volcanoes spew water and ammonia ice. "The physical processes shaping Titan are much the same as those shaping Earth," said Tomasko.
Astronomers plan to study Titan and more of Saturn's neighborhood for years. Cassini is expected to beam back data until 2008.
Highlights from the Cassini Mission
October 1997 The Cassini-Huygens spacecraft is launched from Cape Canaveral, Florida. It begins a 2.2 billion- mile journey to Saturn.
April 1998 The spacecraft flies by Venus. It picks up speed from the planet's gravity, which helps propel the craft toward Saturn.
August 1999 Cassini-Huygens gets another push as it circles by Earth.
December 2000 Cassini-Huygens flies by Jupiter and gets its final planetary boost. The Galileo spacecraft is also in Jupiter's orbit. The two craft explore the solar system's largest planet together.
June 2004 Cassini reaches its final frontier: the Saturnian system, with its seven rings and many moons. Over the next four years, the craft will study the planet, its rings and nine of its moons.
July 2004 Cassini sends new pictures of Saturn's rings. Some show scalloped, or indented, rings, perhaps caused by the gravitational pull of a regularly passing moon.
August 2004 Cassini's cameras spot two never-before-seen moons around Saturn, bringing to 33 the total of known moons. The new moons are the smallest bodies ever seen orbiting Saturn.
October 2004 Cassini-Huygens makes its first close approach to Titan, flying by the moon at a distance of only 730 miles.
December 2004 The Huygens probe is released from Cassini and begins a 20-day trip to Titan.
January 2005 The probe successfully lands on Titan.