A $12 million instrument package designed and built by theUniversity of Colorado at Boulder for the Cassini Mission to Saturn will beused to probe the planet's spectacular ring system, bizarre moons andatmospheric gases.
Slated for launch Oct. 13 from Cape Canaveral, Fla., the spacecraftwill travel 2 billion miles during a roundabout, 6.7-year journey to theringed planet. The $3.3 billion project, the most ambitious planetarymission ever mounted, is managed for NASA, the European Space Agency andthe Italian Space Agency by the Jet Propulsion Laboratory in Pasadena.
Upon its arrival in 2004, the spacecraft will spend four yearsorbiting Saturn and many of its 18 known moons, providing a flood of newdata on what many view as a miniature solar system. Professor LarryEsposito, chief scientist on CU's Ultraviolet Imaging Spectrograph, orUVIS, said it will be used to study the atmosphere of Saturn, the surfacesand atmospheres of its moons and the structure and dynamics of the fabulousring system.
Cassini consists of an orbiter equipped with 12 scientificexperiments and a probe carrying six instrument packages that willparachute into the thick atmosphere of Titan, Saturn's largest and mostintriguing moon.
Two CU spectrometers on board the orbiter will take "chemicalfingerprints" of Saturn's atmospheric gases and measure their temperaturesand compositions, said Esposito, a researcher at CU's Laboratory forAtmospheric and Space Physics. UVIS also will be used to analyze theatmosphere of Titan, which is 10 times denser than Earth's and is thoughtto contain nitrogen and a wealth of hydrocarbons, the building blocks oflife.
"When Voyager flew by Titan in 1980, some thought there might be achance to detect evidence of life there," said Esposito, also a professorin CU's astrophysical and planetary sciences department. Even thoughTitan's temperature was later measured at a frigid minus 290 F -- dashingmost hopes for life -- many scientists believe it may resemble a primordialEarth.
Scientists also think Titan's surface may contain lakes of liquidmethane and ethane, and that organic molecules may constantly be rainingdown from the moon's thick clouds onto its surface. "In many ways, Titanis like a little world," said Esposito. "We should be able to look back intime and see what types of pre-biological chemistry are occurring. Itcould be much like the pre-biotic chemistry present on early Earth, or itcould 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, isheld in place by two "shepherd" satellites and remains one of Saturn's mostexotic features.
"Saturn's rings have a very violent history," he said. "I thinkthey were created by the break-up of a small moon perhaps 100 million yearsago. The fact that we can view Saturn's rings today may be due purely tochance. I expect at some point all the ring material may reform itselfinto 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'swaves, which appear to be tied to gravitational tugs from Saturn's innersatellites, can spiral somewhat like the grooves in a phonograph record orripple 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 scientistsbetter understand the behavior of Saturn's rings, the UVIS photometer onCassini is 50 times more sensitive and will be able to resolve ringphenomena five times smaller than Voyager could. Saturn's ring particlesare thought to consist of ice and rock and range in size from sugargranules to houses.
To view the rings, the CU-Boulder team will use a process known asstellar occultation, focusing the photometer on a bright star behind therings. As the spacecraft passes by the rings, the brightness of the starwill fluctuate as ringlets and ring gaps pass in front of it, allowingresearchers to determine very fine details in Saturn's ring structure anddynamics, Esposito said.
In addition, the ring system "will provide a local lab of sorts tohelp 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 includesEsposito and co-investigators George Lawrence, Bill McClintock, CharlesBarth, Ian Stewart and Justin Maki, a 1996 graduate now at JPL. Cassiniwill be launched on a Titan IV/Centaur rocket built by Denver's LockheedMartin.
"CU has been building ultraviolet spectrometers for NASA since theMars missions in the early 1970s," said Esposito. "The main thing we havelearned from our planetary exploration experience is that there will alwaysbe surprises and serendipitous discoveries."
A fourth instrument on UVIS is a hydrogen-deuterium absorption celldesigned and built with the participation of the Max Plank Institute ofLindau, Germany. Since all the universe's deuterium -- a heavy form ofhydrogen -- is thought to have formed during the big bang, the ratio of thetwo 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 briefglimpses of the riveting planetary system. "But the Cassini effort is anintensive, four-year mission," said Esposito. "We can investigate, ask newquestions 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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