TOKYO--Since 1994, when comet Shoemaker-Levy 9 plunged to its spectacular demise on Jupiter, astronomers have wondered whether any records of similar older impacts exist. Now their curiosity should be at least partly satisfied: A Japanese engineer and amateur astronomer, Isshi Tabe, hit pay dirt while digging through old manuscripts in the library of the Paris Observatory.
Tabe found a drawing made by the famous 17th century astronomer Giovanni-Dominique Cassini, then director of the Paris Observatory. Cassini had recorded how a spot on Jupiter--much like the dark bruises Shoemaker-Levy left on the planet's gassy surface--varied over 18 days after it first appeared on 5 December 1690. "I was really surprised," says Tabe, who says he didn't think people did such detailed astronomical drawings before the 1800s. His analysis will appear next month in the Publications of the Astronomical Society of Japan.
The drawing has intrigued those who have seen it. "The variation over time looked very much like that of Shoemaker-Levy 9," says Junichi Watanabe of Japan's National Astronomical Observatory in Tokyo. "It was really exciting."