Post by Sowelu on Apr 25, 2006 0:39:04 GMT -5
This story relates to Ed's post from the other day.
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Self-destructing comet to flash close by
10:30 24 April 2006
NewScientist.com news service
Kimm Groshong
Astronomers will soon be treated to a close-up celestial show, with a fragmenting comet streaming across the sky in more than 30 chunks. Comet 73P/Schwassmann-Wachmann 3 has been breaking up since 1995, but between 12 and 14 May will come closer to the Earth than any comet since 1983.
Fortunately no threat is posed to Earth since, even at its closest, the nearest of the pieces will be twenty times more distant than the Moon.
But astronomers around the world will take advantage of the relatively close pass. The Hubble and Spitzer Space Telescopes will join with dozens of ground-based facilities for the observation campaign. And scientists expect the brightest comet pieces to be visible through binoculars and possibly, faintly, to the naked eye.
By studying the materials exposed by the break-up, astronomers hope to learn more about the interior of comets, where pristine ingredients from the solar system's earliest days are thought to be preserved. For that reason, some astronomers view the event as a free version of NASA's comet-busting Deep Impact mission.
Bursts of brightness
They also hope to gain insight about how and why such comets become fragmented. For largely unknown reasons, Comet 73P broke into as many as five pieces in 1995. Gravitational forces are known to tear apart some comets, such as the famous Comet Shoemaker-Levy 9 which ended its existence with a spectacular crash into Jupiter. But Comet 73P follows a 5.4-year solar orbit that does not bring it close enough to Jupiter or the Sun for gravitational tugs to be the culprit.
The initial trigger that set Comet 73P's fragmentation process in action in 1995 is still a matter of speculation. "We suspect that rotation may contribute, but it may not be rotation alone. It could be that thermal stresses are also contributing," says Zdenek Sekanina, a cometary physicist at the Jet Propulsion Laboratory in California, US.
A clue may come from the chronology of observations in 1995. Astronomers observed two sudden bursts of brightness from the comet in September and November. Then in December, observers caught the first glimpse of Comet 73P in its piecemeal form.
Such flare-ups are thought to be caused by the sublimation of newly exposed ice from the interior of the comet. Splitting comets have often been detected because of these flare-ups. But it remains unclear whether the outbursts actually cause comets to split or are simply an after-effect of a split that occurred through other processes.
Missing pieces
In any case, comet 73P is still breaking up. The remnant of the parent comet is known as component C and other pieces have been given letter names progressing through the alphabet. And as of this week, astronomers have reached named 37 fragments.
Some of the pieces have survived two orbits around the Sun since the original divide in 1995. But others have been lost. For example, components A, D, E and F have not been spotted this year. They may have broken into pieces too small to see or they may simply be inactive, and therefore invisible. But at least 33 mini-comets may be able to put on a light show when passing Earth.
Some fragmenting comets, such as Comet Biela in the 19th century, have produced meteor showers when flying by our planet. But Paul Wiegert, of the University of Western Ontario, does not expect a meteor shower in May, based on the nature of the 1995 break up.
He says the comet's cloud of debris is not likely to reach Earth until 2022. "But things have changed a little bit because the comet is continuing to break up," he adds. "So it's a little bit hard to say whether we will see meteor showers this year."
www.newscientistspace.com/article/dn9035-selfdestructing-comet-to-flash-close-by.html
____________________________________________________________________________________________________
____________________________________________________________________________________________________
Self-destructing comet to flash close by
10:30 24 April 2006
NewScientist.com news service
Kimm Groshong
Astronomers will soon be treated to a close-up celestial show, with a fragmenting comet streaming across the sky in more than 30 chunks. Comet 73P/Schwassmann-Wachmann 3 has been breaking up since 1995, but between 12 and 14 May will come closer to the Earth than any comet since 1983.
Fortunately no threat is posed to Earth since, even at its closest, the nearest of the pieces will be twenty times more distant than the Moon.
But astronomers around the world will take advantage of the relatively close pass. The Hubble and Spitzer Space Telescopes will join with dozens of ground-based facilities for the observation campaign. And scientists expect the brightest comet pieces to be visible through binoculars and possibly, faintly, to the naked eye.
By studying the materials exposed by the break-up, astronomers hope to learn more about the interior of comets, where pristine ingredients from the solar system's earliest days are thought to be preserved. For that reason, some astronomers view the event as a free version of NASA's comet-busting Deep Impact mission.
Bursts of brightness
They also hope to gain insight about how and why such comets become fragmented. For largely unknown reasons, Comet 73P broke into as many as five pieces in 1995. Gravitational forces are known to tear apart some comets, such as the famous Comet Shoemaker-Levy 9 which ended its existence with a spectacular crash into Jupiter. But Comet 73P follows a 5.4-year solar orbit that does not bring it close enough to Jupiter or the Sun for gravitational tugs to be the culprit.
The initial trigger that set Comet 73P's fragmentation process in action in 1995 is still a matter of speculation. "We suspect that rotation may contribute, but it may not be rotation alone. It could be that thermal stresses are also contributing," says Zdenek Sekanina, a cometary physicist at the Jet Propulsion Laboratory in California, US.
A clue may come from the chronology of observations in 1995. Astronomers observed two sudden bursts of brightness from the comet in September and November. Then in December, observers caught the first glimpse of Comet 73P in its piecemeal form.
Such flare-ups are thought to be caused by the sublimation of newly exposed ice from the interior of the comet. Splitting comets have often been detected because of these flare-ups. But it remains unclear whether the outbursts actually cause comets to split or are simply an after-effect of a split that occurred through other processes.
Missing pieces
In any case, comet 73P is still breaking up. The remnant of the parent comet is known as component C and other pieces have been given letter names progressing through the alphabet. And as of this week, astronomers have reached named 37 fragments.
Some of the pieces have survived two orbits around the Sun since the original divide in 1995. But others have been lost. For example, components A, D, E and F have not been spotted this year. They may have broken into pieces too small to see or they may simply be inactive, and therefore invisible. But at least 33 mini-comets may be able to put on a light show when passing Earth.
Some fragmenting comets, such as Comet Biela in the 19th century, have produced meteor showers when flying by our planet. But Paul Wiegert, of the University of Western Ontario, does not expect a meteor shower in May, based on the nature of the 1995 break up.
He says the comet's cloud of debris is not likely to reach Earth until 2022. "But things have changed a little bit because the comet is continuing to break up," he adds. "So it's a little bit hard to say whether we will see meteor showers this year."
www.newscientistspace.com/article/dn9035-selfdestructing-comet-to-flash-close-by.html
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