Astronomers are Poised for the ‘Crash of 1994’: Boom Or Bust?

If comets are like “dirty snowballs,” as Fred Whipple proposed in the early 1950s, then Jupiter is about to suffer the embarrassment of being hit by a boomerang snowball as astronomers around the world watch. Like many snowballs, Comet Shoemaker‐Levy 9 broke apart in mid‐flight. Comet SL9 was first seen, already in orbit around Jupiter, in March 1993, by a trio of avid comet hunters: Carolyn and Gene Shoemaker of the US Geological Survey in Flagstaff, Arizona, and David Levy, a contributing editor to Sky & Telescope magazine. By May of last year the comet’s orbit had been determined. It was realized by Brian Marsden (Smithsonian Astrophysical Observatory, Cambridge, Massachusetts) that in July 1992, SL9 had come within 95 000 km of Jupiter’s center of mass, where it experienced tidal forces sufficient to rip it apart. On its next pass, SL9 will aim to come within 30 000 km of Jupiter’s center of mass. Because the planet’s radius is about 71 000 km, Jupiter will suffer a direct hit. Astronomers will be on hand to evaluate its injuries, if any.