Rings of Jupiter to have been excited in 1995, around the time of the impact of Comet Shoemaker-Levy 9 with Jupiter, while the smaller set appears to date to the first half of 1990. "Galileo"'s November 1996 observations are consistent with wavelengths of and , and vertical amplitudes of and , for the larger and smaller sets of waves, respectively. The formation of the larger set of waves can be explained if the ring was impacted by a cloud of particles released by the comet with a total mass on the order of 2–5 × 10 kg, which would have tilted the ring
Eugene Merle Shoemaker Institute in 1965. Coming to Caltech in 1969, he started a systematic search for Earth orbit-crossing asteroids, which resulted in the discovery of several families of such asteroids, including the Apollo asteroids. Shoemaker advanced the idea that sudden geologic changes can arise from asteroid strikes and that asteroid strikes are common over geologic time periods. Previously, astroblemes were thought to be remnants of extinct volcanoes — even on the Moon. In 1993, he co-discovered Comet Shoemaker–Levy 9 using the 18-inch Schmidt camera at Palomar Observatory. This comet was unique in that it provided the first opportunity to observe the planetary