University Of Chicago Instrument Ready To Begin Four-year Study Of Saturn's Rings

Cassini will become the first spacecraft ever to enter Saturn's orbit at precisely 9:30 p.m. CDT June 30. NASA launched Cassini in October 1997. The University's instrument, called the High Rate Detector, has quietly recorded sporadic dust impacts in interplanetary space during the mission. "We have seen some impacts, but only a few, maybe one a month. That's about all you'd expect," said Anthony Tuzzolino, a Senior Scientist at the University of Chicago's Enrico Fermi Institute.

But that could change on June 30, after Cassini passes through a gap between two of Saturn's rings. The rings consist of billions of objects ranging in size from microscopic particles to car-sized boulders locked into orbit around the planet.

"The project chose a virtually void section to pass through the ring system so we didn't get clobbered," Tuzzolino said. "After ring-plane crossing, then we start the measurements of the trapped dust in Saturn's system."

The $3 billion Cassini-Huygens mission is the most complex that has ever flown, involving 260 scientists from the United States and 17 European nations. Cassini and its Huygens probe are equipped with a total of 18 instruments. Cassini will release Huygens for a descent to the surface of Titan, Saturn's largest moon, in December.

During the next four years, Cassini will orbit Saturn 76 times along different orbital planes and execute 52 close encounters with the planet's 31 known moons. The University of Chicago detector will collect data the entire time as a component of a larger instrument, the German Cosmic Dust Analyzer. Together the two instruments will study the physical, chemical and dynamical properties of trapped Saturnian dust and its interactions with the planet's rings, icy moons and magnetosphere.

The High Rate Detector instrument, which was built by Tuzzolino and tested with help from Thanasis Economou, Senior Scientist in the Enrico Fermi Institute, will measure particles ranging in size from twice the diameter of a human hair to particles 100 times smaller. The German instrument will measure even smaller particles.

The University of Chicago instrument is capable of detecting 100,000 particles per second as they collide with two small detectors mounted on the larger German instrument. "I wanted that capability, and it's paid off many times," said Tuzzolino, who has contributed his expertise to dozens of NASA missions during the last four decades.

Last January, an instrument similar to the Cassini detector flew aboard the Stardust spacecraft during its encounter with Comet Wild 2. "On Stardust we had 2,000 counts in less than one second," Tuzzolino said. "You must have a high counting rate capability to make these kind of measurements."

And from 1999 to 2002, another Chicago dust detector flew aboard an Air Force satellite to study orbital debris. During that mission, the instrument detected a cloud of tiny debris particles that was scattered into space when the upper stage of a Chinese rocket unexpectedly exploded in orbit in 2000. The detection marked the first time that scientists had been able to link ultra-small particles to the break-up of a particular satellite.

Tuzzolino looks forward to more unexpected results from Saturn and its moons. "There's a lot for us to learn," he said.