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NASA Cassini Spacecraft Marks Mission Halfway Point

28 June 2006

Discoveries to date include three new moons, Titan's similarity to Earth

Washington -- As the Cassini spacecraft reaches the halfway mark in its four-year tour of the Saturn system, discoveries made during the first half of the mission have scientists eager to find out what is in store for the second act.

Cassini has been orbiting Saturn since June 30, 2004, studying the planet and its rings and moons, according to a June 27 press release from the NASA Jet Propulsion Laboratory (JPL) in California.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency (ESA) and Agenzia Spaziale Italiana, the Italian space agency.

"The spacecraft has spent a considerable amount of time studying the moon Titan during 15 separate flybys so far,” said Cassini program manager Robert Mitchell at JPL. In the second half of its prime mission, ending in June 2008, Cassini will swing by Titan 30 more times."

Mission managers focused on Titan because they thought it could tell them something about the early Earth, said Toby Owen, Cassini interdisciplinary scientist at the University of Hawaii in Manoa.

"Examining this world frozen in time, we find evidence that Earth may have begun with the same methane-ammonia atmosphere that marked the birth of Titan. Because of our world's closeness to the sun, Earth has oceans of liquid water, which Titan lacks,” Owen said.

The resulting chemistry in Earth's warm environment ultimately led to the origin of life, but Titan has only methane, nitrogen and a suite of small organic molecules.

"Our planet's carefully balanced, warm global climate is the underlying reason that we are investigating Titan, instead of Titanians investigating Earth," Owen added.

Cassini's tour of the Saturn system is about to take on a new pace.

"This summer we will begin our express-ticket ride," said Jerry Jones, Cassini chief navigator at JPL. "That's 11 months with 17 Titan encounters and 51 spacecraft maneuvers to adjust the flight path, more than one maneuver per week."

The first of these encounters will be a Titan flyby on July 2, followed by the closest Titan encounter yet on July 22, at 950 kilometers above the surface.

Later in July, navigators will begin to flip the spacecraft's orbit orientation with respect to the sun by nearly 180 degrees, resulting in a bird's-eye view of Saturn's rings. This gradual transfer will take about one year.

The wealth of information from the Cassini spacecraft and ESA’s Huygens probe, which descended through Titan's murky atmosphere to its surface, shows that Titan is remarkably Earth-like.

There is evidence for methane rain, erosion, drainage channels, dry lake beds, possible volcanoes and vast dune fields that run for miles. Cassini also discovered three new moons, and some of the previously known moons provided surprises.

One of the most bizarre discoveries is a giant mountain range that runs the full length around the equator of Saturn's moon Iapetus. The mountains rival Olympus Mons on Mars, which is nearly three times the height of Mount Everest. Other moons look like rubble piles.

Cassini also acquired the highest-resolution images ever taken of the planet's rings. Strange structures in the rings became apparent on the first day of the tour. Waves rip through the rings, and knots and banded structures shape them.

Clumps of ice several kilometers wide are now appearing. Scientists also witnessed moons influencing the rings.

The moon Prometheus was caught stealing particles from the F-ring, and Enceladus seems to be contributing particles to Saturn's expansive E-ring. A whole new class of small moonlets may lie within Saturn's rings, scientists believe.

New rings also have appeared, which may indicate the presence of tiny moonlets.

The true showstopper was the discovery of giant, icy geysers gushing from the surface of Enceladus. This evidence leads some scientists to believe there may be liquid water close to the surface.

Mission images and information are available at the NASA Web site.

Text of the press release also is available at the NASA Web site.

(Distributed by the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)