The University Record, February 13, 1996

U 'rocket scientists' share Galileo mission successes

By Sally Pobojewski
News and Information Services

As the theme from "2001: A Space Odyssey " boomed through Rackham Auditorium last Wednesday evening, the U-M's very own "rocket scientists " took the stage to share new data from the Dec. 7 Galileo probe of Jupiter's atmosphere with about 500 members of the University community and the general public.

Titled "Galileo Probes Jupiter: Unlocking the Mysteries of a Giant Planet," the lecture was the second in a monthly series of public presentations on current issues called "Evenings at the Rackham," organized by the Horace H. Rackham School of Graduate Studies.

"The U-M has a long and broad tradition of space exploration dating to the beginning of the U.S. space program," said George R. Carignan, associate dean for graduate education and research in the College of Engineering. Carignan described how he and other scientists and research engineers in the U-M Space Physics Research Laboratory designed and built an electronic sniff-and-sort device called a mass spectrometer for the Galileo probe.

The instrument was designed to take 6,000 air samples at precise l/2-second intervals throughout the probe's plunge into Jupiter's atmosphere and identify the type and quantity of gases in each sample. "The instrument worked precisely as planned" during the 58-minute descent, Carignan said.

Sushil Atreya, professor of atmospheric and space sciences, added that many things had to go precisely as planned in order for the Galileo spacecraft to travel 550 million miles to Jupiter and begin its scientific mission. "Getting to Jupiter is not easy," Atreya said.

After traveling 50,000 miles on two separate trajectories, for example, both probe and orbiter had to meet five months later at the same precise point 130,000 miles over Jupiter's cloud tops.

"The entry angle of the probe had to be perfect," Atreya said. "If the angle varied from eight and one-half degrees, the probe would have either skipped off the top of the atmosphere into space or burned up almost immediately."

Atreya said the atmosphere in the control room was tense during an agonizing six-minute delay on Dec. 7 before scientists received confirmation that the orbiter was receiving data from the descending probe. But since then, U-M scientists have been eagerly poring over the probe data transmitted back to Earth from the Galileo orbiter.

"Everytime we go to a different planet, we discover things that shock and surprise us," said Thomas M. Donahue, the Edward H. White Distinguished University Professor Emeritus of Planetary Science. Jupiter is no exception.

As opposed to Earth, for example, Jupiter's winds appear to speed up the deeper you go into the atmosphere. Scientists found much less water than they expected and much more of the inert gases like krypton and xenon.

A series of bombardments with icy comets during Jupiter's formation 4.5 billion years ago could account for the additional gases, but it doesn't explain the mystery of the missing water, according to Donahue.

"We have all the right conditions to form thick layers of cumulus water clouds like those on Earth, but we saw only wispy clouds and haze," Atreya said. "The probe may have entered the atmosphere in a clear zone with few clouds or perhaps there is some mechanism preventing thick cloud formation."

Finding the answers to Jupiter's mysteries will keep scientists busy for quite some time, according to Donahuewho ended his presentation by telling the audience he wanted to go home so he could get back to analyzing the data.

Two additional free, public "Evenings at the Rackham" are scheduled for this term. On March 19 in a presentation titled "A Visit to the Gallery," the Museum of Art will host a pre-publication reading of new poems inspired by works of art in the Museum's permanent collection. On April 9, U-M alumnus and civil rights activist Roger Wilkins will discuss "Welfare Reform and American's Future." All lectures are free and open to the public.