Number 73 (Story #3), March 27, 1992 by Phillip F. Schewe and Ben Stein COMETS MAY BE MORE ROCK THAN ICE . A reanalysis of images recorded in the 1980's by the Infrared Astronomical Satellite (IRAS) has turned up large dust streaks (seen only in the infrared) trailing behind many inner-solar-system comets. The amount of dust can add up to a considerable fraction---up to three fourths---of the comet's mass. (Science News, 14 Mar. 1992.)