Probe Lands on Moon of Saturn

An image of Saturn's moon Titan from the European Space Agency Web site after the Huygens probe beamed data including this image back to Earth through its Cassini mothership, which is orbiting Titan. (European Space Agency Via AP)

The 700-pound Huygens probe was launched in 1997 aboard Cassini, a joint NASA, ESA and Italian Space Agency mission to the solar system's sixth planet. Cassini is designed to explore Saturn's neighborhood for four years but could go on far longer -- until it runs out of fuel or its 12 instruments wear out.

The mission's first high point came June 30, when Cassini arrived after its seven-year transit and used a spectacular 90-minute rocket burn to speed through Saturn's rings and settle into orbit.

During the mission, Cassini has planned many close "flybys" of Saturn's moons, and 45 of the 52 encounters are aimed at Titan, which is Saturn's largest moon and is larger than the planets Mercury and Pluto.

Cassini released the gold-colored, flying saucer-shaped probe on Christmas Eve, imparting a spin of seven revolutions per minute to hold it stable on a three-week journey to Titan. Huygens had no propulsion of its own and essentially traveled like a large bullet until its approach to Titan triggered a series of onboard "alarm clocks," signaling the probe to begin its descent sequence.

As this process unfolded Friday morning, scientists, reporters and space officials from all over the world gathered at ESA's European Space Operations Center in this Frankfurt suburb -- hoping to celebrate one of the greatest successes in the history of space exploration.

After a round of speeches and a televised review of the probe's scientific capabilities, tension in the crowded theater rose palpably as Huygens reached the top of Titan's atmosphere.

Nobody could know immediately what had happened. Cassini, orbiting Saturn overhead, had pointed its instruments toward Titan to scoop up every scrap of data that Huygens could send. Hours would elapse before Cassini turned back to upload its precious cargo of data to receivers on Earth.

In the meantime, however, the team had aimed a set of Earth-based radio telescopes at Titan in hopes of detecting Huygens's first signals as they were sent to Cassini. Hearing that transmission would mean the probe's crucial maneuvers had been completed.

The sound "is like the dial tone from cell phones," said astronomer Leonid Gurvitz, in charge of the Earth-based radio telescope project.

But there was no guarantee of hearing the signal, said ESA's Southwood: "It's like looking for a needle in a haystack, but much harder."

The sequence began at 5:13 a.m. EST when Huygens entered Titan's atmosphere traveling 13,500 mph, its heat shield braking its progress to 870 mph within three minutes.

Then came the critical moments. The first pilot parachute deployed, pulling a back panel off the probe and allowing the larger 27-foot main parachute to take over. Seconds later, Huygens dumped the heat shield, turned on its instruments and began collecting data.

Fifteen more minutes passed. The main chute was jettisoned, replaced by a drogue to ensure that the descent would last 2 1/2 hours, long enough to gather as much atmospheric data as possible and still leave the batteries with power to conduct ground experiments.

"We will be comfortable the moment we see the third parachute deployed," Claudio Sollazzo, head of Huygens's operations team, had said earlier in the week. If the Earth stations picked up the signal, the team would know the heat shield was gone and at least some instruments were running.

"We have good news," ESA's television commentator announced at 5:39 a.m. EST as applause and cheering erupted. "A network of radio telescopes has tracked the Huygens probe from Earth."

"Huygens is talking to us," Southwood said. "The baby's out of the womb." But, he added, "we haven't counted the fingers yet."

For that, the science team had to wait until computers in mission control began receiving Cassini's transmissions. For many in the room, the data's successful arrival marked the culmination of a life's work -- a quarter-century of planning, research and, finally, results.

"I spent today watching my life pass before my eyes," said a visibly emotional Diaz. "It's just incredible. There will only be one first successful landing on Titan, and this was it."