When scientists want to study antimatter on Earth, they have to accelerate particles to dizzying speeds and smash them together to create tiny amounts of it. Solar flares, brilliant explosions among the most powerful in the solar system, are much more efficient at churning it out. The results of the most detailed study yet of a solar flare, which will be published in the October 1 issue of Astrophysical Journal Letters, indicate that each burst can create up to a pound of antimatter. Furthermore, the material behaves differently than expected.

Robert Lin of the University of California at Berkeley and his colleagues used NASA's Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft to study a solar explosion in July 2002. "We are taking pictures of flares in an entirely new color, one invisible to the human eye, so we expect surprises, and RHESSI gave us a couple already," Lin remarks. Specifically, RHESSI analyzed the gamma rays that are emitted when antimatter annihilates particles of regular matter in the sun's atmosphere. Conventional wisdom holds that flares generate antimatter in dense regions of the sun's atmosphere, because the larger number of particles increases the number of high-speed collisions capable of producing it. Because antimatter is also destroyed through collisions with ordinary matter, researchers expected most of it to be obliterated in the same high-density areas. Instead, the team found evidence of antimatter destruction in regions with surprisingly low numbers of ordinary particles.

It remains unclear whether the flares transport the antimatter from one region to another or generate antimatter in lower-density regions of the atmosphere. Adding to the mystery, the scientists discovered that the explosions sort the particles that they accelerate to close to the speed of light according to their masses or electric charge. Notes Craig DeForest of the South West Research Institute in Boulder, Colorado: "The result is as surprising as gold miners blasting a cliff face and discovering that the explosion threw all the dirt in one direction and all the gold in another direction."