Three-ton science experiment to cruise South Pole skies for cosmicrays (Forwarded)

University of Chicago News Office
Chicago, Illinois

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Steve Koppes, (773) 702-8366,

Nov. 17, 2003

Three-ton science experiment to cruise South Pole skies for cosmic rays

University of Chicago scientists plan to launch an unmanned balloon into the
highest reaches of the atmosphere over Antarctica in early December to hunt for
tiny particles from interstellar space called high-energy cosmic rays.

Consisting of atomic nuclei -- subatomic scraps of matter -- cosmic rays
continually bombard Earth from all directions at nearly the speed of light.
"It's an almost century-old question: where do cosmic rays come from?" said
Dietrich Müller, University of Chicago Professor in Physics, who heads the
project. "We have learned a lot, but we have not found everything yet."

The balloon will carry Müller's 3-ton instrument to an altitude of almost
130,000 feet for up to a month to detect and identify the chemical composition
of cosmic rays that have been accelerated to an energy of a quadrillion
(1,000,000,000,000,000) electron volts. This is 1,000 times more energy than is
generated by the most powerful man-made particle accelerator, the Tevatron at
Fermi National Accelerator Laboratory.

These are the highest energies at which Müller's team can hope to observe a
cosmic ray particle before it strikes molecules in the atmosphere and disappears
in a cascade of secondary particles. Even higher-energy cosmic rays do occur,
but their rarity makes them virtually impossible to detect during a weeks-long
balloon experiment.

According to prevailing theory, shock waves of exploding stars (supernovae) from
within the galaxy sweep up the particles that Müller studies and accelerates
them to extremely high speeds. Exploding stars lack the power to account for the
highest-energy cosmic rays, which may come from outside the galaxy.

"If this supernovae theory holds, there should be a cutoff," Müller said.
Supernovae can probably accelerate particles up to a certain energy, "then they
become inefficient." The theory predicts that experimenters should see a higher
proportion of iron nuclei as particles reach higher and higher energies. "Nobody
has ever really verified this," he said.

The experiment, funded by the National Aeronautics and Space Administration, is
a follow-up to a study conducted aboard the space shuttle Challenger in 1985.
The data from that experiment, built by Müller and the late Peter Meyer, remain
the most detailed ever obtained on the composition of cosmic rays at extreme
energies.

Müller has good reason to travel to Antarctica to conduct this long-duration
balloon experiment. "The balloon remains at a stable altitude without requiring
ballast to be dropped if there is continual sunshine, which only is the case in
Arctic or Antarctic summer," Müller said.

Müller had originally planned to launch his experiment from Fairbanks, Alaska,
and fly around the Arctic Circle, but international red tape got in the way.
"This launch was cancelled year after year because NASA and its Russian
counterpart could not reach an agreement of overflight over Russian territory,"
he said. Only this year did it become possible to launch a balloon with a 3-ton
payload from Antarctica's McMurdo Station.

"We often sit there for weeks and wait for the stratospheric wind pattern to be
just right," said Müller, a veteran of approximately two dozen balloon launches.
"You also cannot launch if you have strong winds on the surface."

The huge helium balloon that will carry Müller's experiment to the top of the
atmosphere has enough plastic to shroud the Sears Tower, which stands 1,450 feet
tall. Launching such a large balloon often leads to a race against the clock.
"The meteorologists must guarantee that for the next two hours the wind is not
going to shift. It can be a bit nerve-wracking," Müller said.

Once launched, the balloon will be at the mercy of the prevailing winds as it
makes one and possibly two journeys around the South Pole collecting data. The
experiment will end when scientists send a radio signal that will trigger a
mechanism to cut the balloon from the payload, which is equipped with a parachute.

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