New Results Suggest X‐Ray Emission is a Common Property of Comets

Comets—dubbed “dirty snowballs” by comet guru Fred Whipple—are among the last celestial bodies you'd expect to emit x rays, which typically come from matter at least as hot as $106 K.$ But last year, to the surprise of astronomers, Carey Lisse (University of Maryland) and Mike Mumma (NASA's Goddard Space Flight Center) discovered faint x‐ray emission from comet Hyakutake. They observed the photogenic comet with the ROSAT satellite as the comet flew by Earth in March 1996. That same month, Mumma and Vladimir Krasnopolsky (Catholic University of America) detected the comet with the Extreme Ultraviolet Explorer (EUVE) satellite.