... Or a high-energy flash?

Kenneth Brecher of Boston University has a different idea about what might have killed the dinosaurs. He speculates that a gamma-ray burst may have done them in indirectly Gamma-ray bursts are mysterious flashes of high-energy radiation that come from random directions in the sky. The origin of the vast majority of these energetic pulses is unknown, but a few have been associated recently with distant galaxies.

In line with recent estimates of the energy of gamma-ray bursts, Brecher's scenario would require a flash that radiates an amount of energy equivalent to 10 percent of the sun's mass. If such a burst came within 300,000 light-years of our galaxy, it could vaporize the outer layers of myriad small comets thought to lie in the Oort Cloud, he calculates. The explosively vaporized material could act as a propellant, flinging some of the smallest, least massive comets--those with a diameter of 1 km or less--into the inner solar system. Some might have fallen to Earth and may even have caused the death of the dinosaurs, Brecher says.

Lawrence A. Molnar of the University of Iowa in Iowa City notes that the population of small comets in the Oort Cloud is unknown, and Brecher admits his work is highly speculative. None of the gamma-ray burst experts present at his talk found serious fault with the conjecture, however, and Brecher says the report may spark new studies on the local influence of the bursts.