Comets

New calculations show Mars may have been stripped of a thick atmosphere that allowed water to flow over the now-desolate planet because it was bombarded by comets or asteroids. In the past, astronomers have advanced several theories about how Mars might have lost much of its atmosphere, but "none of these proposals has gained general acceptance," said H.J. Melosh and A.M. Vickery of the University of Arizona's lunar and planetary laboratory. In a study published in the British journal Nature, the researchers presented computer calculations that they said indicated collisions with large, fast-moving bodies, such as comets, may have triggered Mars's atmospheric loss.

A leading science museum has quietly shaken up the universe by suggesting that Pluto is not necessarily a planet but may be just a lump of ice. The suggestion comes from scientists at the Rose Center for Earth and Space, which opened last year at the American Museum of Natural History in New York. There is a model of Jupiter hanging from the ceiling at the center. There are Saturn with its rings, Mercury, Venus, Earth, Mars, Neptune and Uranus.

Astronomers are getting a close-up view of the death throes of a comet as it passes Earth and enters the inner solar system. Comet 73P/Schwassmann-Wachmann 3 has broken into more than 40 fragments as it speeds toward a swing around the sun June 6, NASA said Thursday. The main fragment will come closest to Earth on May 12, when it will be visible to ground observers. None of the comet's pieces will come close to hitting Earth, NASA said. The closest fragment will pass at a distance of 5.

The first analysis of data from NASA's Stardust probe has shown that comet Wild-2 is not a loose ball of icy rubble, as scientists had expected, but a solid body pockmarked by craters and venting surprisingly patchy jets of gas and dust. The analyses, reported today in the journal Science, reveal a hard but very brittle surface covered with remarkably debris-free craters, 300-foot-high mesas and pinnacles, as well as an unexpectedly large number of narrow jets spewing gas and debris into space.

An odd, greenish, backward-flying comet is zipping by Earth this month, as it takes its only trip toward the sun from the farthest edges of the solar system. The comet is called Lulin, and there's a chance it can be seen with the naked eye, but you'll most likely need a telescope, or at least binoculars, to spot it. It will be closest to Earth on Monday at 7:43 p.m. Pacific time.

Ienjoyed Richard Cromelin's story on the reformed Meat Puppets ["Living to Play Again," June 10]. I've always loved them. Following their recent past saddened me. It's wonderful that Cris [Kirkwood] has come out of his trials and reunited with Curt [Kirkwood]. I wish I'd made it to their Troubadour show. Maybe they'll connect with the Devendra Banhart, Comets on Fire audience that's happening now. CHUCK DUKOWSKI Venice Chuck Dukowski is the founding bass player for Black Flag.

Comet Holmes, ordinarily a rather unremarkable space wanderer that can only be seen with a telescope, can now be seen with the naked eye. The comet threw off its cloak in late October. It had already made its closest pass to the sun and was on its way back out between Mars and Jupiter when it erupted, becoming a million times brighter. Astronomers suspect it was either hit by a space rock or its surface cracked open, permitting the escape of internal gases.

Pristine comet samples returned this weekend by the Stardust spacecraft after a 2.9-billion-mile journey wildly exceeded scientists' expectations, project managers said Thursday. A canister containing particles trapped during the Stardust space probe's 2004 encounter with comet Wild 2 (pronounced Vilt) landed on Earth on Sunday. The samples were taken to the Johnson Space Center in Houston for inspection.

The first results from NASA's Stardust mission to collect material from a comet has turned up a major surprise -- minute fragments of minerals formed under high temperatures rather than the simpler dust scientists had expected.

Researchers have discovered a 300-mile-wide crater hidden under the East Antarctic Ice Sheet, the remnant of an asteroid impact that may have caused the largest mass extinction on Earth. Ohio State University researchers reported at an American Geophysical Union meeting this week that the crater was probably caused by a comet nearly 30 miles wide. The impact occurred about 250 million years ago, during what is known as the Permian-Triassic extinction, when most of life on Earth died.

If this was a preview of the Los Angeles City Section boys' basketball title game, then Woodland Hills Taft has three months to figure out how to stop Westchester's sharpshooting guards. The Comets, ranked No. 1 by The Times, combined for nine three-point baskets to pull away for a 71-62 victory over the second-ranked Toreadors on Saturday night in the championship game of the Westchester tournament. Senior Jordin Mayes had two three-pointers on the way to 24 points and senior Kareem Jamar made five three-point baskets and finished with 19 points for Westchester (4-0)

An odd, greenish, backward-flying comet is zipping by Earth this month, as it takes its only trip toward the sun from the farthest edges of the solar system. The comet is called Lulin, and there's a chance it can be seen with the naked eye, but you'll most likely need a telescope, or at least binoculars, to spot it. It will be closest to Earth on Monday at 7:43 p.m. Pacific time.

Comet Holmes, ordinarily a rather unremarkable space wanderer that can only be seen with a telescope, can now be seen with the naked eye. The comet threw off its cloak in late October. It had already made its closest pass to the sun and was on its way back out between Mars and Jupiter when it erupted, becoming a million times brighter. Astronomers suspect it was either hit by a space rock or its surface cracked open, permitting the escape of internal gases.

Ienjoyed Richard Cromelin's story on the reformed Meat Puppets ["Living to Play Again," June 10]. I've always loved them. Following their recent past saddened me. It's wonderful that Cris [Kirkwood] has come out of his trials and reunited with Curt [Kirkwood]. I wish I'd made it to their Troubadour show. Maybe they'll connect with the Devendra Banhart, Comets on Fire audience that's happening now. CHUCK DUKOWSKI Venice Chuck Dukowski is the founding bass player for Black Flag.

Comets, the lonely wanderers credited with seeding Earth with the ingredients for life, are proving to be far more complex than anyone thought, containing a "zoo" of materials including some that may predate the sun, scientists reported Thursday. And enough mixing was happening in the early solar system to send material from the proto-sun into deep space, where it could be picked up by comets, the scientists reported, speaking at an American Geophysical Union meeting.

Researchers have discovered a 300-mile-wide crater hidden under the East Antarctic Ice Sheet, the remnant of an asteroid impact that may have caused the largest mass extinction on Earth. Ohio State University researchers reported at an American Geophysical Union meeting this week that the crater was probably caused by a comet nearly 30 miles wide. The impact occurred about 250 million years ago, during what is known as the Permian-Triassic extinction, when most of life on Earth died.

Astronomers are getting a close-up view of the death throes of a comet as it passes Earth and enters the inner solar system. Comet 73P/Schwassmann-Wachmann 3 has broken into more than 40 fragments as it speeds toward a swing around the sun June 6, NASA said Thursday. The main fragment will come closest to Earth on May 12, when it will be visible to ground observers. None of the comet's pieces will come close to hitting Earth, NASA said. The closest fragment will pass at a distance of 5.

The first results from NASA's Stardust mission to collect material from a comet has turned up a major surprise -- minute fragments of minerals formed under high temperatures rather than the simpler dust scientists had expected.

Pristine comet samples returned this weekend by the Stardust spacecraft after a 2.9-billion-mile journey wildly exceeded scientists' expectations, project managers said Thursday. A canister containing particles trapped during the Stardust space probe's 2004 encounter with comet Wild 2 (pronounced Vilt) landed on Earth on Sunday. The samples were taken to the Johnson Space Center in Houston for inspection.

NASA's audacious Stardust mission, a seven-year effort to learn more about the origins of the solar system by capturing particles from the tail of a comet and returning them to Earth, ended successfully Sunday when the spacecraft's scorched capsule parachuted into the Utah desert, its cargo intact. The desk-sized capsule glowed red as it streaked across the sky over the northwest United States on its way to a 2:10 a.m. soft landing at the Air Force Test and Training Range in Dugway, Utah.