Astronomers Revel As Shoemaker-Levy 9 Pummels Jupiter

AROUND the world, many planetary scientists are feeling slightly overcome with excitement as they watch the Shoemaker-Levy 9 (SL9) comet fragments pummel Jupiter.

The global information highway swelled with e-mail messages from professional astronomers and amateurs alike as they flashed their sightings and traded tips. As astronomer Stephen Maran at the NASA Goddard Space Flight Center in Greenbelt, Md., put it, this is ``arguably the astrophysical event of our lifetime.''

For the first time ever, astronomers have been able to predict and then observe the impact of one solar system body on another. At press time, about nine of the 21 comet pieces had hit the giant planet. The last fragment will hit early on July 22.

Already, several of the fragments have hit with the explosive energy of many millions of megatons of TNT. That's hundreds of times the explosive energy of the world's stock of nuclear weapons. The impacts have thrown fireball-like plumes of glowing material hundreds of miles above Jupiter's cloud tops. They also have left dark tunnels that now mark the planet's southern region as a series of black spots.

Some scientists, such as the comet's co-discoverer Eugene Shoemaker, have noted in press conferences at the Goddard center that such impacts on Earth would be catastrophically destructive. Dr. Maran says this isn't just hype. He explains that ``the big message [of comet SL9] is it's important to survey the small bodies of the solar system as well as the planets.''

Right now, scientists are focused on what the impacts thus far can tell them about comet SL9 and about Jupiter.

The comet - which is in orbit around Jupiter - broke up two years ago. The parent body passed so close to the giant planet that the tidal forces Jupiter's gravity raised on it pulled the comet apart. Planetary scientists believe the comet was only loosely held together for it to break up so easily. While some fragments also may be fragile, comet specialist Donald Yeomans says some of the larger fragments appear to be a couple of miles across.

Dr. Yeomans, at the California Institute of Technology's Jet Propulsion Laboratory in Pasadena, Calif., is supplying the latest predictions of when each comet fragment will hit Jupiter for observers around the world.

It will takes weeks - even months - for scientists to work through their data enough to begin to learn about Jupiter. They hope the impacts will reveal the composition of the Jovian atmosphere, reveal more about its circulation, and perhaps even send seismic waves deep enough to show details of the planet's core.

Right now, though, many of these scientists are communicating via computer when they are not taking observations. As this reporter discovered when tapping into one network, photos of the impacts taken by the Hubble Space Telescope and other observatories are being put in accessible data banks almost as fast as they are taken. And along with the photos, there are lively discussions about the images in which anyone with a home computer and a modem to access the information highway by telephone can join.