European probe closes in on Saturn moon
(Agencies)
Updated: 2005-01-14 16:07

Nearing the goal of its seven-year voyage, a European space probe on Friday closed in on Saturn's largest moon — Titan — on a mission to explore its mysterious surface and hazy atmosphere, believed to resemble that of a younger Earth.

The European Space Agency's Huygens probe was spun off from the international Cassini mother ship on Christmas Eve and began its free-fall toward the moon's surface. It was to spring to life around 4 a.m. EST Friday just before hitting the upper atmosphere of Titan — the only moon other than Earth's ever to be explored by spacecraft.

In an image released by the European Space Agency ESA on Thursday, June 1, 2004 an artist's impression shows the Huygens landing unit, left, separating from the Cassini orbiter, right, as the spacecraft advances Titan, planet Saturn's biggest moon, bottom left. The Huygens landing device, part of the Cassini-Huygens space mission, is expected to enter the athmosphere of planet Saturn's largest moon and land on the surface of Titan on Friday, Jan. 14, 2005, more than seven years after the Cassini-Huygens mission blasted off for Saturn from Cape Canaveral on Oct. 13 1997. The Cassini-Huygens mission is a joint venture between NASA and the European Space Agency ESA. [AP]

"I expect it to be a very interesting and scientifically challenging moon to visit," Alan Smith, deputy head of operations at ESA told The Associated Press. "The Huygens mission will be the first one to get there, that's why it's so exciting."

Named after Titan's discoverer, the 17th-century Dutch astronomer Christiaan Huygens, the probe carries instruments to explore what Titan's atmosphere is made of and find out whether it has the cold seas of liquid methane and ethane that have been theorized by scientists.

Timers inside the 705-pound probe will awaken it just before it enters Titan's atmosphere. Huygens is shaped like a wok and covered with a heat shield so that it that can survive the intense heat it will face upon entry.

Huygens will then deploy a series of parachutes to slow its descent to the moon's reddish surface, expected to take about 2 1/2 hours. As it descends, the probe will shed its heat shield and deploy its special camera and instruments to begin collecting information on wind speeds and the makeup of Titan's atmosphere. This data will then be transmitted back to Cassini, which will relay it to NASA's Deep Space Network in California and on to ESA controllers in Darmstadt, Germany.

Titan is the only moon in the solar system known to have a significant atmosphere. Rich in nitrogen and containing about 6 percent methane, the Titanic atmosphere is 1 1/2 times thicker than Earth's.

"Its atmosphere is thought to be somewhat like that of the Earth when the Earth was first formed," Smith said. "So people could extrapolate from the measurements they make back to the atmosphere of the early Earth."

Part of a $3.3 billion international mission to study the Saturn system, Huygens is also equipped with instruments to study Titan's surface upon landing. Scientists don't know exactly what it will hit when it lands at about 20 mph.

"It could land on something solid ... it could land in liquid methane, which is what they think a lot of the black seas on Titan are," Smith said. "Because the temperature is so cold and the pressure is so high, gases like ethane and methane exist in liquid form, so it could well land in a sea of methane."

The probe floats and should survive such a landing, despite the temperature of minus 292 degrees Fahrenheit. One hazard would be landing on a solid slope in a position that doesn't permit a strong signal back to Cassini.

Engineers at ESA are counting on the probe to have at least three minutes to transmit information and images from Titan's surface before its battery runs out or Cassini gets out of range.

The Cassini-Huygens mission, a project of NASA, ESA and the Italian space agency, was launched on Oct. 15, 1997, from Cape Canaveral, Fla., to study Saturn, its spectacular rings and many moons.

During the nearly seven years Cassini took to reach the ringed planet, the attached probe was powered through an umbilical cable and awakened from sleep mode every six months for tests.

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