SPRINGTIME FOR COMET HALE-BOPP. Now past its prime in the dusk sky, Hale- Bopp was first spotted two years ago as far away as seven astronomical units, allowing astronomers to observe the thawing process at an earlier stage than is usual for comet watches. This in turn permitted the detection of trace species not before seen on comets, such as SO₂ and H₂CS (Science News, 21 April). What else do we know? First of all, the size of the comet nucleus is estimated to be 27-42 km, at least three times bigger than that of Comet Halley. Of the cometary products vaporized on the inward trip toward the sun, the chief gases are H₂O, CO, and CO₂, which seem to be the main constituents of interstellar ice as well. Dust jets are rich in crystalline olivine, and dust production in general was more than 100 times stronger than with Halley at comparable distances. Variations in the vented jet activity will be used to determine Hale-Bopp's rotation rate. Chemical composition suggests that the comet comes from the Oort Cloud rather than the Kuiper Belt. (Several articles in Science, 28 March.)