Earth probe descends towards Saturn moon

The European probe Huygens descended towards the Saturn moon Titan on Friday, culminating a seven-year quest covering 2,1-billion kilometres to explore one of the greatest enigmas of the solar system.

The unmanned craft plunged into Titan’s roiling atmosphere at the start of a parachute glide in which it will measure the moon’s intriguing weather system and atmospheric gases, scientists said.

Mission controllers—worried that the most ambitious interplanetary mission attempted to date would end disastrously—shouted for joy when Huygens sent a radio signal, proving that it had survived the buffeting entry.

“The baby is alive,” exulted David Southwood, director of science at the European Space Agency (ESA).

But he cautioned: “We still have a long way to go. The baby is out of the womb, but we still have to count the fingers and toes.”

The historic signal was picked up by the Green Bank listening station in West Virginia in the United States and by the Parks antenna in Australia’s New South Wales.

Claudio Solazzo, mission operations chief, said a clam-like shield was designed to protect Huygens from friction heat as it hurtled in from deep space at 20 times the speed of sound and collided with Titan’s atmosphere.

“The first thing will be the opening of one small parachute. Soon after that, the main parachute, 8m wide, will open.
After that, all the instruments will be [turned] on. It will be a clockwork process,” Solazzo said.

The 319kg craft’s instruments are to film Titan’s surface, measure wind speed and pressure and analyse atmospheric gases as it descends to the surface over two-and-a-half hours.

So little is known about Titan that it is unclear as to exactly when and where it will touch down. The site could be a hard surface of methane ice, or rock, or possibly a chemical sea.

Whatever the circumstances, the instruments were designed to carry on monitoring for another three minutes.

Only when data was to be received later on Friday would anyone know whether the huge gamble has been a success, said Huygens scientist Leonid Gurvits.

By 6pm GMT, “all data from the mission will have been acquired and released to the scientists, and scientific work can actually begin at this point”, Solazzo said.

Titan was chosen because it is the only moon in the solar system that has a substantial atmosphere.

Its thick mix of nitrogen and methane is suspected to be undergoing chemical reactions similar to those that unfolded on Earth billions of years ago. That process eventually provided the conditions for life on our planet.

“Titan is a time machine. It will especially provide us with the opportunity to know about the conditions on our early Earth,” Alphonso Diaz, Nasa science assistant administrator, told reporters at Huygens mission control, the European Space Operations Centre.

The mission is conducted in tandem with the Nasa orbiter Cassini, which gave Huygens a piggyback ride from Earth to Saturn, a voyage that began in 1997 and ended in their separation off Titan on December 25.

Cassini circled overhead on Friday in order to pick up data from Huygens and then relay it back to Earth.

The transatlantic tie-up, costing $3,2-billion, “is another example of what cooperation means”, said ESA director general Jean-Jacques Dordain.

“It has been a tremendous 25 years of hard work for more than 200 scientists from 19 different countries.”

After the ambitious one-day Huygens mission, Cassini will continue a four-year survey of Saturn, the solar system’s largest planet after Jupiter.

Huygens is named after the Dutch astronomer Christiaan Huygens, who discovered Titan in 1655. Cassini‘s name comes from the Italian Jean-Dominique Cassini (1625-1712), who discovered the Saturnian satellites Iapetus, Rhea, Tethys and Dione.

In 1675, he discovered what is called the Cassini Division, the gap between Saturn’s rings.—Sapa-AFP

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