Magazine article Science News

Crash Course on a Comet Bound for Jupiter

Magazine article Science News

Crash Course on a Comet Bound for Jupiter

Article excerpt

Lined up like pearls on a string, some 20 comet-like fragments will slam one by one into Jupiter next July. The impacts will allow at least two spacecraft -- Galileo and Voyager 2 - to observe directly the most powerful series of collisions ever predicted for the solar system.

On that much, astronomers agree. But the amount of energy unleashed by the fragments, known collectively as Comet Shoemaker-Levy 9, remains a matter of intense debate. That's because researchers don't know the size, and hence the kinetic energy, of any of the pieces, which were discovered last March and are thought to originate from a parent body ripped apart by Jupiter's gravity in July 1992 (SN: 6/26/93, p.410).

Several studies reported this week may help astronomers estimate the size of the largest fragments. Researchers described their findings during a crash course on Comet Shoemaker-Levy 9 - a marathon four-hour session at the annual meeting of the American Astronomical Society's Division for Planetary Sciences in Boulder, Colo.

At the meeting, Harold A. Weaver of the Space Telescope Science Institute in Baltimore presented several snapshots of Comet Shoemaker-Levy 9 taken on July 1 with the Hubble Space Telescope. Although the images represent the highest resolution of the fragments to date, astronomers still can'[ clearly distinguish the hard core of each body from its comet-like shroud of dust and gas. Weaver estimates that the highly reflective shrouds, known as comas, account for some 70 percent of the luminosity of the fragments in the Hubble pictures. By subtracting this estimated contribution, Weaver and his colleagues calculate that the largest pieces have a core no greater than about 5 kilometers in diameter - about half the size of early estimates.

The kenetic energy of each fragment is proportional to its mass, which in turn is proportional to the cube of the fragment's diameter. …

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