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No one understands why the points of impact are so dark -- a mystery that may take months to solve -- but it's clear that they are very high up in Jupiter's atmosphere, since the planet's familiar stripes can be seen through them. Astronomer Heidi Hammel of M.I.T. says the collisions will provide an opportunity to study the winds above Jupiter's cloud tops. "The mark left by the first impact is already starting to be spread around," she observes. There are also hints of seismic waves -- ripples thatmay have traveled all the way to a dense layer of liquid hydrogen thousands of miles down and then bounced back up to the surface, creating rings half the size of the planet's visible face. These waves may offer clues to Jupiter's internal structure.
The spots that were made by the collisions will undoubtedly blow away eventually -- though no one knows how long it will take -- but it's much too soon to tell whether there will be any permanent changes in Jupiter. There is still every chance that the impacts, especially from the four fragments that hit in nearly the same place last Wednesday and Thursday, will destabilize the atmosphere and create a new, permanent cyclone like Jupiter's Great Red Spot.
It's also possible that the show isn't quite over. Theorists at NASA'S Jet Propulsion Laboratory argue, on the basis of a computer model of S-L 9, that debris -- including boulders several hundred feet across -- has lagged behind the original 21 major fragments. These stragglers, they predict, will keep hitting Jupiter through September. Unlike the participants in last week's show, however, some of the later pieces may smash into the near side of the planet, giving astronomers a chance to watch some strikes directly. Is the theory plausible? Says Weaver: "These are the same guys who said the pieces were big and that the impacts would be huge. They were right, and lots of others were wrong. We've had so many surprises from Shoemaker-Levy 9 already that I wouldn't rule anything out."