Number 122 (Story #2), April 6, 1993 by Phillip F. Schewe and Ben Stein THE FORMATION OF THE INNER PLANETS from low-mass planetesimals may have happened quickly, in as little as a million years, new simulations show. These results were reported by Douglas Lin of UC Santa Cruz and his colleagues in the 20 January Astrophysical Journal. The whole process of rocky-planet building, beginning with the first solid-material grains in the solar system about 4.56 billion years ago (and still preserved in meteorites), and continuing with the growth and repeated collisions of larger and larger objects in the extended circumstellar disk, took perhaps 100 million years. This model in which planet condensation was quick and rocky seems to be displacing the older model of the solar system in which planets precipitated slowly from a more gaseous disk (Science News, 20 Mar.). As for the outer planets, a separate study by George Wetherwill of the Carnegie Institution indicates that the formation of planets as large as Saturn and Jupiter should be rare since there would have been only a short time for them to fashion cores and then to accumulate such massive atmospheres from matter in the circumstellar disk before the disk dissipated. (Science News, 27 Mar.)