Suspected Asteroid Collision Leaves Odd X-Pattern of Trailing Debris
February 2, 2010: Something awfully curious is happening 100 million miles from Earth in the asteroid belt. There's a newly discovered object that superficially looks like a comet but lives among the asteroids. The distinction? Comets swoop along elliptical orbits close in to the Sun and grow long gaseous and dusty tails, as ices near the surface turn into vapor and release dust. But asteroids are mostly in circular orbits in the asteroid belt and are not normally expected to be "volatile."The mystery object was discovered on January 6, 2010, by the Lincoln Near-Earth Asteroid Research (LINEAR) sky survey. The object appears so unusual in ground-based telescopic images that discretionary time on NASA's Hubble Space Telescope was used to take a close-up look. The observations show a bizarre X-pattern of filamentary structures near the point-like nucleus of the object and trailing streamers of dust. This complex structure suggests the object is not a comet but instead the product of a head-on collision between two asteroids traveling five times faster than a rifle bullet. Astronomers have long thought that the asteroid belt is being ground down through collisions, but such a smashup has never before been seen.
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WASHINGTON — NASA's Hubble Space Telescope has observed a mysterious X-shaped debris pattern and trailing streamers of dust that suggest a head-on collision between two asteroids. Astronomers have long thought the asteroid belt is being ground down through collisions, but such a smashup has never been seen before.
Asteroid collisions are energetic, with an average impact speed of more than 11,000 miles per hour, or five times faster than a rifle bullet. The comet-like object imaged by Hubble, called P/2010 A2, was first discovered by the Lincoln Near-Earth Asteroid Research, or LINEAR, program sky survey on Jan. 6. New Hubble images taken on Jan. 25 and 29 show a complex X-pattern of filamentary structures near the nucleus.
"This is quite different from the smooth dust envelopes of normal comets," said principal investigator David Jewitt of the University of California at Los Angeles. "The filaments are made of dust and gravel, presumably recently thrown out of the nucleus. Some are swept back by radiation pressure from sunlight to create straight dust streaks. Embedded in the filaments are co-moving blobs of dust that likely originated from tiny unseen parent bodies."
Hubble shows the main nucleus of P/2010 A2 lies outside its own halo of dust. This has never been seen before in a comet-like object. The nucleus is estimated to be 460 feet in diameter.
Normal comets fall into the inner regions of the solar system from icy reservoirs in the Kuiper Belt and Oort Cloud. As a comet nears the sun and warms up, ice near the surface vaporizes and ejects material from the solid comet nucleus via jets. But P/2010 A2 may have a different origin. It orbits in the warm, inner regions of the asteroid belt where its nearest neighbors are dry rocky bodies lacking volatile materials.
This leaves open the possibility that the complex debris tail is the result of an impact between two bodies, rather than ice simply melting from a parent body.
"If this interpretation is correct, two small and previously unknown asteroids recently collided, creating a shower of debris that is being swept back into a tail from the collision site by the pressure of sunlight," Jewitt said.
The main nucleus of P/2010 A2 would be the surviving remnant of this so-called hypervelocity collision.
"The filamentary appearance of P/2010 A2 is different from anything seen in Hubble images of normal comets, consistent with the action of a different process," Jewitt said. An impact origin also would be consistent with the absence of gas in spectra recorded using ground-based telescopes.
The asteroid belt contains abundant evidence of ancient collisions that have shattered precursor bodies into fragments. The orbit of P/2010 A2 is consistent with membership in the Flora asteroid family, produced by collisional shattering more than 100 million years ago. One fragment of that ancient smashup may have struck Earth 65 million years ago, triggering a mass extinction that wiped out the dinosaurs. But, until now, no such asteroid-asteroid collision has been caught "in the act." 本帖最后由 MBR 于 2010-2-6 15:20 编辑
1# MBR
整合翻译了下····翻译后看见图片版有同志已经发了 ···嘎嘎···
2010年1月6日，林肯近地小行星探索机构在距离地球1.4亿公里的小行星带上，发现了一颗具有彗星特征的神秘天体。这颗天体在地面观测站的图像中显得极不寻常，以至于动用了哈勃空间望远镜在1月25和29日自由支配时间对其进行了详细的观测。观测结果显示，一个奇异的X型丝状结构出现在类似天体的内核位置上，并且出现尾随的尘埃带。这个复杂的结构说明这个天体不是一颗彗星，而是两颗小行星以至少5倍子弹的速度迎面相撞。因为彗星沿着椭圆轨道向太阳运动，当靠近太阳时，表面的冰挥发成蒸汽，并出现长长的由气体和尘埃组成的彗尾。而小行星基本上位于小行星带中，观测到“挥发”这种现象是不寻常的。
小行星碰撞场面还是比较震撼的，平均冲撞速度大于每小时11000英里。这颗编号为P/2010 A2的天体具有不同于普通彗星的光滑尘埃外围，其中央核区位于其自身尘埃晕之外，核区直径估计有460英尺（140米），中央核区附近类X型丝状结构由尘埃，砾石组成，可能是来自中央核区，一部分由于太阳的辐射压力而形成长长的尘埃条纹，这些尘埃镶嵌在丝状结构上，形成随动的尘埃斑点。普通彗星一般来自太阳系边缘柯伊伯带和奥尔特云，当彗星靠近太阳时，表面的冰层被加热蒸发，固体彗核形成物质喷流。这意味着P/2010 A2可能有不同的源头，它的轨道位于小行星带内侧，温度相对暖和，轨道附近的天体以干燥的岩石类为主，缺少挥发性物质，而且该丝状结构不同于哈勃以往拍摄的普通彗星，所以这两者间具有不同的机理，这也是为什么地面观测站的光谱分析显示其中缺少气体。X型丝状结构更可能是由于两个天体碰撞后产生的情景，而不是由冰层简单地挥发产生。
小行星带上隐藏着远古碰撞丰富的证据，存在着大量古老天体的碎片。P/2010 A2的轨道与花神族小行星一致，而花神族小行星由一亿多年前的行星大碰撞产生的。来自这次远古大碰撞的碎片很可能在6500万年前袭击了地球，使恐龙灭绝。这次观测从某种意义上说是为人类“直播”了一次小行星间的碰撞。到目前为止，天文学家一直认为小行星带是由大量碰撞而产生的碎片带，如此直观地拍摄到小行星间的碰撞还属首次。 2·········长········· 顶~~~~~::070821_09.jpg::::070821_13.jpg:: 3# MBR 欢迎楼主以后多发发其他网站的文章，哈勃官网的就让给我好啦，这个论坛中哈勃的翻译文章，几乎都是我发的。ESO的也留给我吧 呵呵··好滴···· 五倍子弹速度撞击是一个怎样的概念，这图片好壮观了！ 不知道楼主是否有时间、有兴趣翻译这篇文章
http://www.astronomynow.com/news/n1002/01browndwarf/ astronomynow那边，我比较经常去看···
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