Searching for Antimatter From Space

The space shuttle Discovery will blast into orbit on 2 June to test out a detector designed to probe the universe for antimatter. This is the first search for antimatter to be conducted from space--far from the interfering effects of Earth's atmosphere. The aim of the 10-day mission, described by project scientists during a Kennedy Space Center briefing today, is to ensure that the Alpha Magnetic Spectrometer (AMS) is up to snuff for its real task: a 3-year hunt for antimatter aboard the International Space Station.

Antimatter is extremely rare. Only a few antiparticles have been seen--and these were painstakingly created in accelerators, only to vanish within a fleeting instance. But physicists have wondered why the stuff is so scarce, as the big bang 15 to 20 billion years ago should have spewed equal numbers of particles and antiparticles. There are many theories, but few facts. Samuel Ting, a physicist at the Massachusetts Institute of Technology, initiated the AMS project to look for primary antimatter left over from the big bang to help sift through the various theories.

The AMS detector is designed to spot antimatter by magnetically bending particles and antiparticles--which have opposite charges--in different directions. Silicon strips inside the detector can map out the trajectory of anything that enters, and this trajectory reveals the intruder's charge and mass. Although searches for antimatter have in the past been carried out on balloons, Ting says that this detector will be up to 10,000 times more sensitive because it is well above Earth's atmosphere, which is full of particles that would annihilate any antimatter.

But one expert doubts that AMS will pick up any useful information either on this trip or on its stint on the space station. Recently published work, says Greg Tarle, an astrophysicist at the University of Michigan, Ann Arbor, suggests that the detector is not sensitive enough to see the extremely sparse antiparticles of antimatter leftover from the big bang.

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