From Volume 3, Issue Number 52 of EIR Online, Published Dec. 28, 2004

SCIENCE & TECHNOLOGY
Huygens Ready to Pierce Titan's Veil
by Marsha Freeman

While many of us are enjoying our family and friends this Christmas Day, a few dozen scientists and engineers around the world will be anxiously awaiting word from a spacecraft more than 800 million miles away. They will hope to hear that a little probe has been sent on its way, toward a close encounter with Saturn's moon, Titan.

The Cassini spacecraft has been carrying along the Huygens probe since it was launched in October 1997. On July 1, Cassini entered into orbit about the great ringed planet, and on Christmas Day it will interrupt its comprehensive study of Saturn, Saturn's rings, and its family of planets, in order to position itself properly for the release of the probe.

Huygens will be out of touch with Earth during its cruise phase toward Titan, but even awaiting word from the mother ship will take time. Cassini will have its antenna turned toward the probe and Saturn to achieve precise pointing for the release of Huygens. After it points its antenna back to Earth for transmission, it will take 67 minutes for its report to reach here.

After being released from Cassini, Huygens will follow a ballistic (unpowered) trajectory toward Saturn's planet-sized moon Titan. On Jan. 14, it will take the plunge through Titan's atmosphere. This will be the first set of in situ measurements and observations of Saturn's great moon.

Cassini itself has already made two flybys of Titan, each time revealing yet a little more of what is below its mysterious nitrogen veil.

It is hoped that Huygens will descend through Titan's hazy atmosphere, and return data, via the orbiting Cassini, for two hours. If it survives the descent, it may land on a solid, liquid, or oozy surface. It is still anybody's guess.

- Titan's Changing Weather -

The advantage in having a spacecraft in orbit around a planet, rather than just flying by it, has already been demonstrated in terms of Titan.

When Cassini made a flyby of the Mercury-sized moon on Oct. 26, at a distance of about 123,000 miles from the surface, white clouds near the south pole of the body were clearly visible. They were noted, but had also been observed through ground-based telescopes.

After the flyby, what did cause a sensation was the first set of radar images ever taken of Titan's surface, through the clouds. The images showed distinct regions of light and dark, indicating smooth and rough, or textured, surface features.

Debate continues as to whether volcanic, aeolian (wind-blown), meteorological, or other geological processes have created such a set of varied surface features. Does Titan have smooth regions because it somehow avoided the periods of heavy meteor bombardment evident on other Saturnine moons? Or does it have some flowing process that covered over or filled in the craters?

While the scientists were studying the first radar images and discussing hypotheses, Cassini was gathering more data.

On Dec. 13, the spacecraft made another flyby. It swept by as close as 750 miles. From a photograph taken at about 139,999 miles from the moon, it was evident that in the two months between visits, several extensive patches of clouds had formed in higher, more temperate latitudes, in addition to the clouds at the south pole.

"We see for the first time, discrete cloud features at mid-latitudes, which means we see direct evidence of weather," reported Dr. Kevin Baines, a member of the Cassini science team.

Scientists propose that the changes in Titan's atmopshere could be meteorological—a function of seasonal variations in the body's temperature.

Seasonal shifts in global winds on Titan could circulate in the upper atmosphere, forming clouds, according to astronomers watching Titan from telescopes in Hawaii. If the clouds are seasonal, scientists expect them to drift northwards over the next few years, as southern summer goes into autumn.

But if the clouds are being caused by geological changes, such as a "warm spot" on the surface, or a slushy methane geyser spouting out material, the cloud feature may just stay at its current mid-latitude.

Using adaptive optics, which subtract from telescope observations distortions caused by the atmosphere, astronomers on the ground are supplementing the work that Cassini and Huygens are doing on the scene.

During its most recent Titan flyby, Cassini was also able to take a stunning image of Titan's dark, or night, side (facing away from the Sun), which shows the atmosphere shimmering in its own glow.

Titan has a thick atmosphere, and also layers of haze that are detached from the rest of the atmosphere, and float above it. These layers extend about 250 miles above Titan.

Cassini found that Titan's upper atmosphere consists of a number of layers of haze, which can be seen in ultraviolet images. Even at night, the haze layers scatter light through the atmosphere.

This moon, larger than the planets Mercury and Pluto, has been an object of great interest since its discovery by Christian Huyghens in 1655. A world in its own right, Titan is the only planetary moon known to have a substantial atmosphere.

Because Titan's atmosphere is mainly nitrogen, like the Earth's, with a significant presence of methane and other carbon-based compounds, scientists hope that this strange world will open a window into what the early environment of Earth may have been like, as the context for the development of life.

They hope that in about three weeks, the Huygens probe will provide them with some of the answers.

All rights reserved © 2004 EIRNS