$12 Million CU Instrument Package Headed For Saturn On Cassini Mission

October 02, 1997

A $12 million instrument package designed and built by the University of Colorado at Boulder for the Cassini Mission to Saturn will be used to probe the planet's spectacular ring system, bizarre moons and atmospheric gases.

Slated for launch Oct. 13 from Cape Canaveral, Fla., the spacecraft will travel 2 billion miles during a roundabout, 6.7-year journey to the ringed planet. The $3.3 billion project, the most ambitious planetary mission ever mounted, is managed for NASA, the European Space Agency and the Italian Space Agency by the Jet Propulsion Laboratory in Pasadena.

Upon its arrival in 2004, the spacecraft will spend four years orbiting Saturn and many of its 18 known moons, providing a flood of new data on what many view as a miniature solar system. Professor Larry Esposito, chief scientist on CU's Ultraviolet Imaging Spectrograph, or UVIS, said it will be used to study the atmosphere of Saturn, the surfaces and atmospheres of its moons and the structure and dynamics of the fabulous ring system.

Cassini consists of an orbiter equipped with 12 scientific experiments and a probe carrying six instrument packages that will parachute into the thick atmosphere of Titan, Saturn's largest and most intriguing moon.

Two CU spectrometers on board the orbiter will take "chemical fingerprints" of Saturn's atmospheric gases and measure their temperatures and compositions, said Esposito, a researcher at CU's Laboratory for Atmospheric and Space Physics. UVIS also will be used to analyze the atmosphere of Titan, which is 10 times denser than Earth's and is thought to contain nitrogen and a wealth of hydrocarbons, the building blocks of life.

"When Voyager flew by Titan in 1980, some thought there might be a chance to detect evidence of life there," said Esposito, also a professor in CU's astrophysical and planetary sciences department. Even though Titan's temperature was later measured at a frigid minus 290 F -- dashing most hopes for life -- many scientists believe it may resemble a primordial Earth.

Scientists also think Titan's surface may contain lakes of liquid methane and ethane, and that organic molecules may constantly be raining down from the moon's thick clouds onto its surface. "In many ways, Titan is like a little world," said Esposito. "We should be able to look back in time and see what types of pre-biological chemistry are occurring. It could be much like the pre-biotic chemistry present on early Earth, or it could be vastly different."

Esposito discovered Saturn's fourth known ring, dubbed the "F" ring, in 1979 while analyzing data from Pioneer 11 as it passed by Saturn. The F ring, a braided and kinked ring located far outside the E ring, is held in place by two "shepherd" satellites and remains one of Saturn's most exotic features.

"Saturn's rings have a very violent history," he said. "I think they were created by the break-up of a small moon perhaps 100 million years ago. The fact that we can view Saturn's rings today may be due purely to chance. I expect at some point all the ring material may reform itself into a moon or be ground into dust."

The rings are "incredibly active, exhibiting waves, wakes, ripples, bends and kinks" that seem to wax and wane over time, he said. The ring's waves, which appear to be tied to gravitational tugs from Saturn's inner satellites, can spiral somewhat like the grooves in a phonograph record or ripple like waves on a pond. The researchers hope to resolve how gravity, magnetic energy and other forces hold the enigmatic rings together.

Although a CU photopolarimeter aboard Voyager helped scientists better understand the behavior of Saturn's rings, the UVIS photometer on Cassini is 50 times more sensitive and will be able to resolve ring phenomena five times smaller than Voyager could. Saturn's ring particles are thought to consist of ice and rock and range in size from sugar granules to houses.

To view the rings, the CU-Boulder team will use a process known as stellar occultation, focusing the photometer on a bright star behind the rings. As the spacecraft passes by the rings, the brightness of the star will fluctuate as ringlets and ring gaps pass in front of it, allowing researchers to determine very fine details in Saturn's ring structure and dynamics, Esposito said.

In addition, the ring system "will provide a local lab of sorts to help us understand similar phenomenon in our larger astrophysical system, like spiral galaxies and accretion discs around black holes," he said.

The LASP science team working on the Cassini project includes Esposito and co-investigators George Lawrence, Bill McClintock, Charles Barth, Ian Stewart and Justin Maki, a 1996 graduate now at JPL. Cassini will be launched on a Titan IV/Centaur rocket built by Denver's Lockheed Martin.

"CU has been building ultraviolet spectrometers for NASA since the Mars missions in the early 1970s," said Esposito. "The main thing we have learned from our planetary exploration experience is that there will always be surprises and serendipitous discoveries."

A fourth instrument on UVIS is a hydrogen-deuterium absorption cell designed and built with the participation of the Max Plank Institute of Lindau, Germany. Since all the universe's deuterium -- a heavy form of hydrogen -- is thought to have formed during the big bang, the ratio of the two elements should shed light on the solar system's earliest history.

The only other planetary investigations of Saturn -- Voyager 1, Voyager 2 and Pioneer 11 -- all have all been flybys, providing only brief glimpses of the riveting planetary system. "But the Cassini effort is an intensive, four-year mission," said Esposito. "We can investigate, ask new questions and even reprogram our spacecraft orbits in order to answer them. "The magnitude of discoveries on this mission should be tremendous."

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University of Colorado at Boulder

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