Comet Crash !

For a week in July 1994, the collisions of about 20 fragments of the comet Shoemaker-Levy 9 into the planet Jupiter captured the attention of stargazers around the world. Comet watchers marveled, since the display turned out to be, as one astronomer put it, “the celestial drama of the century.” Why did this event far exceed expectations?

First, the comet fragments, speeding at some 120,000 miles per hour [200,000 kph], produced huge blasts that only the most extreme predictions had indicated. Their entrance into Jupiter’s atmosphere brought forth flashes that lasted just a few seconds. Then, superheated gases shot out of the atmosphere, forming immense fireballs that for the largest blasts briefly exceeded the surface temperature of the sun! Over the next 10 to 20 minutes, a large plume rose as high as 2,000 miles [3,200 km].

Furthermore, what initially were thought to be poor viewing conditions turned out to be nearly ideal. Because the impacts occurred on the darkened side of Jupiter, the brilliant flashes and plumes were more easily detected. In some cases the tops of the plumes could be seen rising above Jupiter’s horizon, and within ten minutes of impact, Jupiter’s rotation brought the impact sites into direct view of the earth. Another ten minutes brought the impact sites into the sunlight. By then, the plumes had dissipated, and they were replaced by huge, dark bruises. These spots—the largest was twice the size of the earth—had not been predicted by astronomers, and yet they turned out to be the most distinct features that could be seen.

The Galileo spacecraft provided direct views of the impacts. In earth orbit, the Hubble Space Telescope viewed the impacts at the wavelengths of visible and ultraviolet light. Other observatories measured the response of the comet blasts at various wavelengths specifically chosen to yield valuable information. At the South Pole, the sun never rose, permitting full-time viewing from the South Pole Infrared Explorer telescope.

Sky watchers have experienced a rare treat. When will the next comet spectacle take place? Comet Hale-Bopp, already visible to the naked eye, may be the brightest comet we see this century. It will pass within 123 million miles [198 million km] of our planet. Comet watchers in the Northern Hemisphere will want to view Hale-Bopp during the month of April 1997. All of this reminds us that we live in a dynamic.

Posted in: Science