Astronomers watched in fascination this past week as pieces of Comet Shoemaker-Levy 9 slammed into Jupiter with the force of a million H-bombs, producing shock waves and sonic booms that rippled outward after each impact, creating new features visible from Earth in the atmosphere of the solar system's largest planet. Observations of these spectacular events promise a rich harvest of important scientific information.
There is evidence the comet fragments have significantly perturbed large regions of Jupiter's atmosphere. The waves may provide ways to explore parts of the planet's atmosphere that are too deep to see through the cloud tops. Astronomers working with the Hubble Space Telescope have watched the blemishes on Jupiter's surface created by the exploding fragments and tracked their movements as clues to what is happening inside and beneath the impact sites.
Meanwhile, the Galileo spacecraft, with the only direct view of the comet collisions, recorded them as they happened. Because the spacecraft's antenna is partially disabled, the first snapshots of the collision probably won't reach Earth until mid-August. But already enough data has been downloaded to show that Galileo has detected flashes of comet fragments burning up in Jupiter's atmosphere. Relatively simple measurements taken by a light meter aboard Galileo detected flashes from comet fragments H, which hit Jupiter on Monday, and L, which hit Tuesday.
The comet provided a natural probe of Jupiter's atmosphere. By penetrating deeply and then exploding, the fragments performed a sort of chemical analysis. Astronomers have used measurements of Jupiter's spectrum to identify molecules in the black patches left by the impacts. Already they have found sulphur, ammonia and hydrogen sulfide, though there's still no sign of water.
The planetary pummeling allowed experts to verify their ability to gauge the size of the comet fragments based on their brightness. That was the scale they used to judge which pieces would be the largest; the impacts proved their calculations correct. By watching how the black impact marks dissipate, scientists can also learn more about the weather and wind currents of Jupiter. It will take many months, perhaps years, to fully analyze all the data produced by this unprecedented event. But already we can be certain that it will vastly enrich our understanding of the outer planets and the solar system in which we live.