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Cassini-Huygens: Mission to Saturn and Titan

by Tobias Owen

On February 9, when Cassini was 43 million miles from Saturn, an onboard camera took a series of exposures that were combined to create this image. Credit: NASA/ JPL/Space Science Institute.

Imagine a planet with more than thirty moons. One of them is larger than Mercury and is enveloped in a nitrogen-filled atmosphere more massive than our own. The planet itself has 95 times the mass of Earth, yet its density is so low it could float in champagne! That would be a truly spectacular cocktail, for this planet is Saturn, the true Lord of the Rings.

A joint US-European space mission called Cassini-Huygens will reach Saturn this summer after a seven-year voyage. The mission consists of an orbiter (Cassini) carrying a probe (Huygens), which will descend into the atmosphere of the giant satellite Titan. "Landfall" with this miniature solar system will occur on June 11, when the spacecraft passes Saturn's most distant satellite, Phoebe, a strange, dark body that moves backward in its orbit around Saturn. On July 1, the spacecraft will cross the planet's ring plane, and a powerful rocket engine will slow it down, sending it into orbit around Saturn. After deploying Huygens on Christmas Day, Cassini will spend the next four years examining Saturn, its magnificent rings, its complex magnetic field and trapped radiation belts, and many of its fascinating satellites. Huygens will enter Titan's atmosphere on January 14, 2005, and then make a 2.5-hour descent to the surface, where it will continue to transmit data if it survives the landing.

Titan is certainly the most intriguing satellite in the solar system, a moon that enables a kind of cosmic time travel. Titan's environment resembles in some respects the conditions on the early Earth before life began. We often think of life developing on Earth in the primordial soup of warm little tide pools. On Titan we will be looking for primordial ice cream, the results of spontaneous organic chemistry still taking place in the atmosphere today, held in deep freeze on the satellite's surface. And that surface may well be extraordinary! Lakes, rivers, rainstorms, and waterfalls of liquid natural gas may sculpt a crater-pocked landscape of frigid ice coated with deposits of organic aerosols. Titan is a flammable world, but its temperature is so low that there is no source of oxygen that would allow it to burn.

IfA astronomer Tobias Owen was one of the originators of the Cassini-Huygens mission and the chair of the U.S. Study Team that began work with the Europeans to develop this mission in 1984. He is presently an interdisciplinary scientist and a member of three of the experiment teams that will be analyzing the rich harvest of data to be returned by the spacecraft. These results will be brought to the IfA for study by our graduate students and for presentation to our classes and to the community.

For more information, see http://saturn.jpl.nasa.gov/index.cfm and http://www.rssd.esa.int/Huygens/Mission/Overview.html

Who were Cassini and Huygens?

Giovanni Domenico Cassini (1625-1712) was an Italian-born French astronomer who discovered four of Saturn's satellites and the division in Saturn's rings that is now named for him. He also measured the rotation periods of Mars and Jupiter, participated in measuring the distance to Mars by triangu-lation, and improved the estimate of the solar system's dimensions.

Christiaan Huygens (1629-95) was the Dutch astronomer who discovered Titan in 1655. While others had observed Saturn's rings, he was the first to correctly interpret what they saw.

Saturn with Cassini-Huygens

Join the great adventure of exploring the Saturn system by checking the Imaging Team Web site, http://ciclops.lpl.arizona.edu/, as Cassini-Huygens reveals new worlds.