Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: MONDAY, July 18, 1994 TAG: 9407180061
SECTION: NATIONAL/INTERNATIONAL PAGE: A-2 EDITION: METRO
SOURCE: By The Baltimore Sun
DATELINE: LENGTH: Medium
An infrared image snapped by the W.M. Keck Observatory in Hawaii early Sunday showed two circular plumes of hot gas glowing white, looking like headlights in the fog, southwest of Jupiter's Great Red Spot.
The plumes marked the locations where fragments "A" and "C" - the first and third of the broken comet's 21 visible pieces - slammed down Saturday afternoon and early Sunday morning.
Four more pieces were expected to have struck the planet by 4 a.m. today, including fragment "G" - one of the largest in the "string-of-pearls" formation, packing 25 times the mass and energy of fragment "A."
"This is just the orchestra warming up," comet co-discoverer David Levy said of the earlier impacts.
Even at a mile or less in diameter, however, "A" was no popgun.
"If `A' had hit North America, it would have made a crater about 20 kilometers [12.4 miles] in diameter," said Eugene Shoemaker, of the Lowell Observatory, the comet's other discoverer.
Had it struck the Earth, "a tremendous amount of pulverized material would have been spread [in the upper atmosphere] . . . causing severe climatic changes - probably the worst natural disaster ever witnessed by man," Shoemaker said.
"We can be very glad this comet was heading for Jupiter and not the Earth," said Dr. Heidi Hammel, an astronomer from the Massachusetts Institute of Technology and imaging team leader for the Hubble Space Telescope.
On Jupiter - composed mostly of hydrogen gas - the cometary missile of ice, rock and organic chemicals is believed to have plunged 100 miles or more into the planet's atmosphere at 130,000 mph.
As fragment "A" was slowed by the increasingly dense atmosphere, scientists believe, its immense kinetic energy was converted quickly to heat - up to 30,000 degrees. That created an expanding bubble of hot gas that rose back through the atmosphere, erupting through the cloud tops as a towering "fireball," or plume, that then swept far above the clouds.
On Saturday, the Hubble Space Telescope made an extraordinary 12-minute series of five photographs showing that plume rising above Jupiter's southwest horizon, then cooling, collapsing and flattening out more than 100 miles above the surrounding clouds of ammonia. The central plume spread out to a diameter equal of a third to a half that of the Earth (2,600 to 3,900 miles).
by CNB