Comet Shoemaker–Levy 9 rarity: one post-impact study estimated that comets in diameter impact the planet once in approximately 500 years and those in diameter do so just once in every 6,000 years. There is very strong evidence that comets have previously been fragmented and collided with Jupiter and its satellites. During the Voyager missions to the planet, planetary scientists identified 13 crater chains on Callisto and three on Ganymede, the origin of which was initially a mystery. Crater chains seen on the Moon often radiate from large craters, and are thought to be caused by secondary impacts of the original ejecta, but the
Carolyn S. Shoemaker Rittenhouse Medal of the Rittenhouse Astronomical Society in 1988 and the Scientist of the Year Award in 1995. The Hildian asteroid 4446 Carolyn, discovered by college Edward Bowell at Lowell Observatory in 1985, was named in her honor. Carolyn Shoemaker is credited by the Minor Planet Center with the discovery of 377 numbered minor planets made between 1980 and 1994. Carolyn S. Shoemaker Carolyn Jean Spellmann Shoemaker (born June 24, 1929) is an American astronomer and is a co-discoverer of Comet Shoemaker–Levy 9. She once held the record for most comets discovered by an individual. Carolyn Jean Spellmann was born