Huygens Set For Center Stage Performance At Titan

SATURN DAILY

When Huygens plunges toward Titan's surface, it will undergo an ordeal far more severe than anything experienced by spacecraft returning to Earth. Titan's atmosphere extends about 600 km above its surface . Traveling at about 2,400 km per hour it will have to decelerate to an impact speed of about 16 feet (5 meters) per second - the equivalent to jumping from a chair to the ground.

Washington DC (SPX) Dec 06, 2004
Many of his fellow Brits may be spending their early morning hours Christmas Day with visions of sugar plums dancing in their heads, but John Zarnecki probably will be dreaming of his upcoming role in a potentially landmark mission.

Zarnecki runs the science surface package aboard the European Space Agency's Huygens probe. On Dec. 25, the Huygens will separate from its perch atop NASA's Cassini spacecraft, which since last July has been orbiting and photographing Saturn in a multi-year mission to study the ringed planet and its 31 known moons - including Titan, the second-biggest in the solar system.

On Jan. 14, Huygens is set to move to center stage when it will plunge though Titan's atmosphere and attempt to land softly on the surface, perhaps ending up afloat on a sea of liquid hydrocarbons - the first human mission to an alien ocean.

It's a distinct possibility that I could be the very first scientist to carry out oceanography on an outer planet of the solar system, said Zarnecki, who is a professor of space science at Britain's Open University in London.

Equally, the probe could land with a thud on hard ground or squelch into a morass of extraterrestrial slime, he added. No one knows for sure.

What comprises the surface of the smog-enshrouded Titan, the only planetary satellite in the solar system with an atmosphere - and one that is 10 times thicker than Earth's - remains largely a mystery.

Astronomers have known about the atmospheric distinction for about 100 years, ever since Spanish astronomer Jose Comas Sola reported markings he interpreted as atmospheric clouds on Titan. The atmosphere was confirmed in 1944 by Gerard Kuiper of the University of Arizona. Kuiper - he of the eponymous belt of objects between Neptune and Pluto - analyzed sunlight reflecting off Titan with a spectrometer and found methane.

Further observations by the Voyager spacecraft in the early 1980s added nitrogen as a major component of the atmosphere, along with traces of ethane, propane and other organic hydrocarbons, all of which are produced by the ultraviolet light from the sun and magnetic particles from Saturn.

Updated information, some of which has been provided by instruments aboard Cassini, shows Titan's atmosphere contains over 95 percent nitrogen, with the balance comprising methane and the other hydrocarbons.

When Huygens finally plunges toward Titan's surface, it will undergo an ordeal far more severe than anything experienced by spacecraft returning to Earth, not to mention the probes that have landed successfully on Mars. Titan's atmosphere extends about 360 miles (nearly 600 kilometers) above its surface, compared with Earth's 37 miles (60 kilometers). Chances are, there will be violent crosswinds at multiple levels on the way down. Only the Galileo spacecraft, which was literally and deliberately destroyed by Jupiter's atmosphere in September 2003, endured something similar.

Traveling at about 1,500 miles (2,400 kilometers) per hour - or twice the speed of sound - when Huygens enter Titan's atmosphere, it will have to decelerate to an impact speed of about 16 feet (5 meters) per second - the equivalent to jumping from a chair to the ground.

That is only the half of it. What lies below those massive clouds is an incredibly cold surface that has been bathed for ages in permanent twilight. There very well may be roiling seas of liquid methane or nitrogen.

Yet for all its strangeness, Titan retains at least one similarity to Earth, something that extends back to its atmosphere. On both planetary bodies, the major atmospheric constituent is nitrogen, and therein lies an intriguing prospect. Titan's atmosphere, with 95 percent nitrogen, is somewhat comparable to Earth's 78 percent.

Obviously, lacking oxygen, Titan almost certainly could not harbor complex and familiar forms of life. But its atmosphere now might be similar to what existed on primordial Earth, back when life first emerged. Therefore Titan might hold clues to conditions that lead to the beginnings of life.

Or, it is not entirely implausible that alien life forms might have sprung forth within Titan's seas.

In any event, Zarnecki said, the instruments onboard have been designed to handle a range of possibilities. Let's just say that after a seven-year voyage and 20 years of planning ... I will be extremely pleased to land, whatever the surface.

Other scientists involved in the mission concur, and acknowledge the staggering idea of a mission requiring such precision taking place at an unprecedented distance.

Superlatives can come easy when talking about space missions, but this particular voyage of scientific discovery is truly awesome, said Ian Halliday, of the Particle Physics and Astronomy Research Council, which funded Britain's participation in the Cassini-Huygens mission.

At a distance of almost 1.3 billion kilometers (789 million miles), Halliday added, that's quite a feat.

SATURN DAILY

Nature's Canvas

Pasadena CA (JPL) Nov 30, 2004
In a splendid portrait created by light and gravity, Saturn's lonely moon Mimas is seen against the cool, blue-streaked backdrop of Saturn's northern hemisphere. Delicate shadows cast by the rings arc gracefully across the planet, fading into darkness on Saturn's night side.

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