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Gas giant's role in preventing asteroid collisions under scrutiny.
For more than a decade many astronomers have thought of Jupiter as a protective big brother for planet Earth. The gas giant's gravitational pull is believed to slingshot incoming Earth-threatening objects out of the Solar System. This has led many to suppose it shielded the young Earth from impacts, helping to support conditions for life.
But now, a preliminary study indicates that Earth would have done just as well, if not better — in at least one regard - without Jupiter's help.
The results of a study presented today at the European Planetary Science Congress in Potsdam, Germany, indicate that Earth would be struck — by one class of objects at least — at nearly the same rate, regardless of whether Jupiter was there or not. The findings are still tentative, cautions Jonathan Horner, an astronomer at the Open University in Milton Keynes who led the new work. But, he says, Jupiter's role as guardian may have been overstated: "It seems that the idea isn't so clear-cut."
The idea of Jupiter as protector was first proposed by planetary scientist George Wetherill in 19941. Wetherill showed that the planet's enormous mass — more than 300 times that of the Earth — is enough to catapult comets that might hit Earth out of the Solar System. Some have also postulated that Jupiter would thin the crowd of dangerous asteroids and other objects, making Earth a more stable home. Other work has suggested that, in the past, changes in Jupiter's orbit might have actually increased the number of objects on a collision course with earth. Until now, Horner says, little work was done to test either idea.
But now, a preliminary study indicates that Earth would have done just as well, if not better — in at least one regard - without Jupiter's help.
The results of a study presented today at the European Planetary Science Congress in Potsdam, Germany, indicate that Earth would be struck — by one class of objects at least — at nearly the same rate, regardless of whether Jupiter was there or not. The findings are still tentative, cautions Jonathan Horner, an astronomer at the Open University in Milton Keynes who led the new work. But, he says, Jupiter's role as guardian may have been overstated: "It seems that the idea isn't so clear-cut."
The idea of Jupiter as protector was first proposed by planetary scientist George Wetherill in 19941. Wetherill showed that the planet's enormous mass — more than 300 times that of the Earth — is enough to catapult comets that might hit Earth out of the Solar System. Some have also postulated that Jupiter would thin the crowd of dangerous asteroids and other objects, making Earth a more stable home. Other work has suggested that, in the past, changes in Jupiter's orbit might have actually increased the number of objects on a collision course with earth. Until now, Horner says, little work was done to test either idea.
單字
1. Jupiter
The fifth planet from the sun, the largest and most massive in the solar system
2. slingshot
A Y-shaped stick having an elastic strap attached to the prongs, used for flinging small stones.
3. preliminary
Prior to or preparing for the main matter, action, or business; introductory or prefatory.
4. struck
Past tense and a past participle of strike
5. tentative
Not fully worked out, concluded, or agreed on; provisional
6. clear-cut
Distinctly and sharply defined or outlined.
7. enormous
Very great in size, extent, number, or degree.
8. comets
A celestial body, observed only in that part of its orbit that is relatively close to the sun, having a head consisting of a solid nucleus surrounded by a nebulous coma up to 2.4 million kilometers (1.5 million miles) in diameter and an elongated curved vapor tail arising from the coma when sufficiently close to the sun. Comets are thought to consist chiefly of ammonia, methane, carbon dioxide, and water.
9. postulated
a proposition that is accepted as true in order to provide a basis for logical reasoning
10. asteroids
any of numerous small celestial bodies composed of rock and metal that move around the sun
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