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Jupiter Takes Huge Blow From Comet : Space: Explosion is described as having hundreds of times the combined energy of all nuclear weapons on Earth. Fireball briefly outshines the planet itself.

July 19, 1994|ROBERT LEE HOTZ | TIMES SCIENCE WRITER

An immense fragment of a dying comet hit Jupiter so hard early Monday that the blast momentarily blinded the world's largest optical telescope and sent awed astronomers around the world scrambling for superlatives to describe the impact.

At NASA's Goddard Space Flight Center in Maryland, which is coordinating reports on the ongoing collision of Jupiter with the pieces of a shattered comet, astronomers estimated the force of the impact at 6 million megatons of TNT--hundreds of times the combined energy in all the world's nuclear weapons.

The impact of Fragment G, as the two-mile-wide piece of Comet Shoemaker-Levy 9 is designated, created a fireball that briefly outshone Jupiter itself, scientists said. An equally large fragment hit late Monday and another of similar size was expected to hit Wednesday.

The impact, the most powerful planetary explosion ever observed, sent superheated gases spewing thousands of miles into space from a planet already marred by black scars left by nine chunks of comet debris that have fallen since Saturday. The fragment plunged about 60 miles into Jupiter's atmosphere before exploding, scientists estimated.

"The energy released is beyond any of our experiences on Earth," said Lucy McFadden, a University of Maryland astronomer. "Ten thousand megatons is the total energy that we can create on Earth with bombs."

Jupiter's black eye, as planetary scientist Heidi B. Hammel dubbed the enormous, circular plume erupting from the giant planet Monday, is approximately 9,600 miles across and, during its peak at 12:51 a.m. PDT, rose more than 1,300 miles into space, scientists said. Hammel is leading the team of scientists gathered in Maryland to analyze the images produced by NASA's Hubble Space Telescope.

"The fact that G got as bright as Jupiter itself in the infrared (a heat measurement) means that we're dealing with a very big object," said Eugene Shoemaker, an astronomer at the Lowell Observatory in Flagstaff, Ariz., and one of the discoverers of the comet. "It's a big wallop."

Astronomers watching the fireworks through the largest optical telescope in the world--the W.M. Keck Observatory on Mauna Kea in Hawaii--said the unusual flare was so bright that it overwhelmed the instrument's infrared sensors, briefly preventing them from recording the impact. "We saw a truly remarkable large plume," said astronomer Imke de Pater, a principal investigator on the Keck Telescope from UC Berkeley. "It completely saturated the telescope."

Viewed by the space telescope through an ultraviolet filter, which can reveal detail not normally visible, the impact site is as large as Jupiter's giant Red Spot--twice as large as Earth.

In the boil of debris and gases rising from the impacts, unusual chemicals never before observed on Jupiter are being detected by Earth-based astronomers.

"They are seeing emissions they have never seen before because they are seeing conditions we have never seen before," said University of Michigan scientist John Clarke, who is monitoring Jupiter's aurora for blast effects.

Jupiter, which has more than 300 times the mass of Earth, is not expected to suffer any long-term damage from the comet. Jupiter is 480 million miles from Earth, too far for the comet to have any influence here, scientists said.

All of the comet fragments are landing on Jupiter's night side, which faces away from Earth. But the planet rotates so quickly, and the fireballs are rising so high above Jupiter's clouds, that the impact sites quickly swing into view of observers on Earth.

The bombardment, which is expected to continue through early Friday, has created enormous public interest, stirring superstitious dread and scientific curiosity in equal measure. It is the first time anyone has been able to watch--even indirectly--as a comet hits a planet.

So much electronic mail concerning observations of Jupiter has been generated by amateur and professional astronomers this week that computer traffic has achieved gridlock at key astronomy interchanges.

At the Jet Propulsion Laboratory, which is maintaining an on-line archive of the comet images and related astronomical data, 45,000 computer users had signed on to the system by lunchtime Monday. Even senior astronomers at the National Aeronautics and Space Administration's Goddard center were having trouble getting access to the latest electronic bulletins from around the world.

The spectacle on Jupiter is stirring new misgivings about Earth's vulnerability to celestial impacts. An object the size of Fragment G can be expected to hit Earth every few hundred thousand years, scientists say, and there are 150 known impact craters on the planet. About 1,000 known objects of this size or larger are in orbits that periodically cross Earth's path; none is on a collision course with Earth, scientists said.

As powerful as Monday's impact appeared to observers here, its force was only a fraction of that generated by celestial objects believed to have struck Earth millions of years ago.

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