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Sulfur detected after comet's impact may explain hues in Jupiter's clouds


The bombardment of Jupiter by the comet P/Shoemaker-Levy 9 is revealing chemicals that scientists say might explain for the first time the yellows, reds and browns of Jupiter's visible clouds.

Delighted astronomers also reported yesterday that they have seen the equivalent of northern lights on Jupiter, but at latitudes farther south than they have ever been seen before. It's an effect they think is caused by the falling comet.

But none of their discoveries or computer enhancements, they say, can match the thrill of putting their eye to a small telescope and seeing the dark impact sites for themselves.

The spots -- Earth-sized clouds of gas and dusty debris blown into Jupiter's stratosphere by the comet impacts and explosions -- are the biggest changes and the most prominent features to appear on Jupiter since Galileo started looking in 1610. And astronomers are urging everyone to find a telescope and have a look.

"This is an extraordinary thing," said David Levy, co-discoverer of Shoemaker-Levy 9. "These spots are a major effect from these collisions. They're easy to see [with modest telescopes and good visibility], and this is the time to do it."

University of Maryland astronomer Lucy McFadden, who is coordinating the worldwide observations, stood in line Tuesday night to view Jupiter through an 8-inch amateur telescope at the UM observatory in College Park.

"There's something visceral about putting your eye to an eyepiece," she confessed. "I took my husband, and he said it was sort of a 'Woodstock' experience.

"I could see the [planet's cloud] bands going across and sort of convinced myself I could see some spots."

Later, through the university's 20-inch telescope, Dr. McFadden said, "I actually saw those spots." A video monitor linked to the telescope showed three impact sites. "I could only discern two with my eyeball."

An estimated 500 people trooped through the College Park observatory Tuesday night to have a look.

The UM observatory's open house has been extended through tomorrow night. Located near University Boulevard and and Metzerott Road, the observatory is open from 8 p.m. to 10 p.m.

The Jupiter watch also continues from 8:30 p.m. to 1 a.m. through tomorrow night at the Johns Hopkins University's Bloomberg Physics Center, near the San Martin Drive entrance of the Homewood campus.

Eighty to 100 people have visited the center each night since the comet show began. Call 516-6525 after 5 p.m. for weather updates.

As astronomers watch, comet fragments continue to rain on Jupiter. The last will hit early tomorrow.

Some of the biggest, tagged "Q1" and "Q2," slammed down between 3:30 p.m. and 4 p.m. yesterday. They were to be followed at 10-hour intervals by somewhat smaller fragments "R"

and "S," all of them headed for the same area in Jupiter's Southern Hemisphere.

An early report on one of the "Q" impacts indicated that it triggered a huge explosion, sending a fiery plume into the planet's stratosphere.

"It's a big one, a very big one," said South African astronomer Brian Carter, who watched the impact through an infrared telescope at the Sutherland mountain-top observatory in South Africa.

The discovery of sulfur at the spot where fragment "G" crashed down Monday morning was reported yesterday at the Goddard Space Flight Center in Greenbelt by University of Arizona astronomer Roger Yelle.

The Hubble Space Telescope's Faint Object Spectrograph detected the signature of sulfur in the ultraviolet light coming from the center of the impact site's gas plume.

Scientists have long suspected that there must be sulfur at somedepth in Jupiter's atmosphere, but it had never been detected before.

Sulfur is one of the best candidates for explaining the yellows, reds and browns seen in Jupiter's uppermost clouds, the ones visible from Earth. But those clouds are known to be made largely of ammonia, and ammonia clouds should be white.

Also, scientists still must figure out whether the sulfur they're seeing really comes from Jupiter's atmosphere, or from the comet.

"I guess we still can't be sure," said astronomer Keith Noll, principal investigator in Hubble's atmospheric spectroscopy experiments.

The "northern lights" spotted on Jupiter were reported by Renee Prange of the French Institute Astrophysique Spatiale, who is also a member of the Hubble upper atmosphere imaging team.

Ultraviolet images shot by Hubble show glowing streaks in Jupiter's Northern Hemisphere that appear as almost mirror images of glows from the impact site of fragment "G" in the Southern Hemisphere.

Dr. Prange said that the northern glows appear further south than ever before. "I think it's a major discovery," she said.

The Jovian auroral displays appear to be triggered by electrically charged particles released during the impacts in the south, and shoot in a looping arc northward along the planet's magnetic field until they fallback into the planet's atmosphere, creating a glow in the north.

It's as if the particles were being repelled from one end of a bar magnet and attracted to the other.

Still unclear, Dr. Prange said, is whether the particles are comet dust that became electrically charged as it fell through the planet's magnetic field, or gas molecules from the planet that became charged in the heat of the fragment's impact and explosion.

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