Dec. 6, 2010:? The Geminid meteor shower, the Summit this year on Dec. 13 and 14, is on the most intense meteor stream of the year. It takes days, is rich in fireballs and from almost anywhere on Earth to see.
It is also a NASA astronomer Bill Cooke favorite meteor shower - but for none of the above reasons.
He explains "The Geminids are my favorite", "because they explanation face."
The most Meteor streams come from comets, which spew rich meteoroids for a night of "Shooting Stars". The Geminids are different. The parent is not a comet but a weird rocky object with the name not explain enough to the Geminids 3200 Phaethon, who has very little dusty dirt.
"Of all debris of stream that passes through every year and Earth, the orbits by far the most massive," says Cooke. "If we dust add the height within the Geminid, it prevails over other streams by factors of 5 to 500."
This makes the orbits of the 900-lb gorilla of Meteor streams. Even more, a 98-pound weakling is 3200 Phaethon.
3200 Phaethon, 1983 by IRAS of NASA satellite was discovered and immediately classified as an asteroid. What could be otherwise? It have no tail; its orbit intersected the main asteroid belt; and its colours strongly resembled that of the other asteroids. In fact, 3200 Phaethon, is similar to asteroids Pallas so much, it could be a 5-km-chip off 544 km block.
"If 3200 Phaethon apart from asteroid Pallas, broken, as some scholars believe, then Geminid meteoroids dirt from the resolution, might be" speculated Cooke. "But not agreed, that with other things that we know."
Researchers have looked at the orbits of Geminid meteoroids carefully and came to the conclusion that they were ejected from 3200 Phaethon when Phaethon was close to the Sun - not as it was breaking out in the asteroid belt with Pallas. The eccentric orbit of 3200 Phaethon brings it well inside the orbit of mercury every 1.4 years. The Rocky body gets so a regular blast of solar heating, the jets of dust in the stream Geminid can cook.
Could this be the answer?
To test the hypothesis, researcher for NASA's twin STEREO turned spacecraft that study on the solar activity. Coronagraphs onboard STEREO detects Sonnenkreutzer asteroids and comets, and in June 2009 she discovered 3200 Phaethon only 15 solar diameter of the Sun's surface.
What UCLA planetary scientist David Jewitt and Jing Li, which analyzes the data next surprised. "3200 Phaethon unexpectedly by a factor of two brightened," she wrote. "The most likely explanation is that Phaethon dust, perhaps in reaction to a breakdown of the surface rock (crack thermal breakage and decomposition of hydrated minerals) ejected in the intense heat of the Sun."
Jewett, and Li's Rock"Comet" hypothesis is convincing, but they do indicate a problem: during his 2009 Sun encounter ejected only 0.01% of the mass of the Creek debris Geminid - not nearly enough added the amount of dust 3200 Phaethon, to the stream filled in over time. Maybe was the rock Comet more active in the past...?
"We simply don't know," says Cooke. "Every new thing that we learn about the orbits seems to deepen the mystery."
This month, Earth debris stream, is produce by the Geminid guided more than 120 meteors per hour of dark sky sites. The best time to look is probably between local midnight and sunrise on Tuesday, December 14, when the Moon is low and twins high overhead, light orbits in a sparkling starry sky spit constellation.
Bundles for out there, and enjoy the secret.
Author: Dr. Tony Phillips | Credit: Science@NASA
没有评论:
发表评论