When Scientific American published an article on the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in March 1999, we were inundated with mail from readers concerned about the planned experiments. We featured one such letter in the "Letters to the Editors" section of the July issue from a reader who wondered whether the experiments could result in the formation of miniature black holes that would devour our planet. Physicist Frank Wilczek of the Institute for Advanced Study in Princeton, N.J. dismissed that possibility in his reply. But he did suggest that the RHIC collisions could spawn a new form of matter dubbed strangelets. The exchange sparked a wave of newspaper stories about how the RHIC experiments might lead to disaster. So Brookhaven director John Marburger asked a team of physicists to review the issue. The group determined that a strangelet--in the unlikely event RHIC created one--would exist only fleetingly and therefore prove harmless.

Now new evidence should erase any remaining doubts about strangelet safety. According to the results of a study that will appear in the November 27 issue of the Physical Review Letters, none of the various sizes of strangelets poses a threat. Jes Madsen of the University of Aarhus in Denmark showed that light strangelets are extremely unstable and heavy strangelets are difficult to forge in the fireball environment of a collision. As for medium-size strangelets, which must have a positive charge, electrostatic repulsion precludes the possibility that they might gobble up nearby positively charged atomic nuclei, as proposed in some of the doomsday scenarios.