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[最新进展]雨燕号测定飞溅物质总量!

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发表于 2005-7-12 13:49 | 显示全部楼层 |阅读模式
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How Much Material Was Blasted Off By Deep Impact?

X-ray detections from Tempel 1 after Deep Impact collision. Image credit: Swift.

Here come the X-rays, on cue. Scientists studying the Deep Impact collision using NASA';s Swift satellite report that comet Tempel 1 is getting brighter and brighter in X-ray light with each passing day.
The X-rays provide a direct measurement of how much material was kicked up in the impact. This is because the X-rays are created by the newly liberated material lifted into the comet';s thin atmosphere and illuminated by the high-energy solar wind from the Sun. The more material liberated, the more X-rays are produced.
Swift data of the water evaporation on comet Tempel 1 also may provide new insights into how solar wind can strip water from planets such as Mars.
"rior to its rendezvous with the Deep Impact probe, the comet was a rather dim X-ray source," said Dr. Paul O';Brien of the Swift team at the University of Leicester. "How things change when you ram a comet with a copper probe traveling over 20,000 miles per hour. Most of the X-ray light we detect now is generated by debris created by the collision. We can get a solid measurement of the amount of material released."
"It takes several days after an impact for surface and sub-surface material to reach the comet';s upper atmosphere, or coma," said Dr. Dick Willingale, also of the University of Leicester. "We expect the X-ray production to peak this weekend. Then we will be able to assess how much comet material was released from the impact."
Based on preliminary X-ray analysis, O';Brien estimates that several tens of thousands of tons of material were released, enough to bury Penn State';s football field under 30 feet of comet dust. Observations and analysis are ongoing at the Swift Mission Operations Center at Penn State University as well as in Italy and the United Kingdom.
Swift is providing the only simultaneous multi-wavelength observation of this rare event, with a suite of instruments capable of detecting visible light, ultraviolet light, X-rays, and gamma rays. Different wavelengths reveal different secrets about the comet.
The Swift team hopes to compare the satellite';s ultraviolet data, collected hours after the collision, with the X-ray data. The ultraviolet light was created by material entering into the lower region of the comet';s atmosphere; the X-rays come from the upper regions. Swift is a nearly ideal observatory for making these comet studies, as it combines both a rapidly responsive scheduling system with both X-ray and optical/UV instruments in the same satellite.
"For the first time, we can see how material liberated from a comet';s surface migrates to the upper reaches of its atmosphere," said Prof. John Nousek, Director of Mission Operations at Penn State. "This will provide fascinating information about a comet';s atmosphere and how it interacts with the solar wind. This is all virgin territory."
Nousek said Deep Impact';s collision with comet Tempel 1 is like a controlled laboratory experiment of the type of slow evaporation process from solar wind that took place on Mars. The Earth has a magnetic field that shields us from solar wind, a particle wind composed mostly of protons and electrons moving at nearly light speed. Mars lost its magnetic field billions of years ago, and the solar wind stripped the planet of water.
Comets, like Mars and Venus, have no magnetic fields. Comets become visible largely because ice is evaporated from their surface with each close passage around the Sun. Water is dissociated into its component atoms by the bright sunlight and swept away by the fast-moving and energetic solar wind. Scientists hope to learn about this evaporation process on Tempel 1 now occurring quickly -- over the course of a few weeks instead of a billion years -- as the result of a planned, human intervention.
Swift';s "day job" is detecting distant, natural explosions called gamma-ray bursts and creating a map of X-ray sources in the universe. Swift';s extraordinary speed and agility enable scientists to follow Tempel 1 day by day to see the full effect from the Deep Impact collision.
The Deep Impact mission is managed by NASA';s Jet Propulsion Laboratory, Pasadena, California. Swift is a medium-class NASA explorer mission in partnership with the Italian Space Agency and the Particle Physics and Astronomy Research Council in the United Kingdom, and is managed by NASA Goddard. Penn State controls science and flight operations from the Mission Operations Center in University Park, Pennsylvania. The spacecraft was built in collaboration with national laboratories, universities and international partners, including Penn State University; Los Alamos National Laboratory, New Mexico; Sonoma State University, Rohnert Park, Calif.; Mullard Space Science Laboratory in Dorking, Surrey, England; the University of Leicester, England; Brera Observatory in Milan; and ASI Science Data Center in Frascati, Italy.
 楼主| 发表于 2005-7-12 14:17 | 显示全部楼层

[最新进展]雨燕号测定飞溅物质总量!

[这个贴子最后由Steed在 2005/07/12 02:18pm 第 1 次编辑]

大意:
利用NASA雨燕号探测器研究深度撞击的科学家们报告说,在过去的每一天中,坦普尔1号彗星在X射线中的亮度正变得越来越明亮。
X射线可以直接测量撞击溅起了多少物质。这是因为X射线是由新释放出来的物质被高能太阳风照射而产生出来的。被释放的物质越多,产生的X射线也就越多。
雨燕号对坦普尔1号彗星的水份蒸发的测量也可以提供新的视角,来理解太阳风是如何从行星,例如火星上,剥离水份的。
“在与深度撞击探测器遭遇以上,这颗彗星是个相当暗淡的X射线源,”雨燕小组成员Paul O';Brien博士说。“当你将一颗铜制探测器以每小时超过20,000英里的速度撞击一颗彗星时,一切都改变了。现在我们检测到的大部分X射线都是来自于撞击产生的碎屑。我们能够对被释放物质的总量做出一个可靠的测量。”
“撞击后,表面和表面以下的物质需要花费几天时间才能达到彗星的上层大气,即彗发,”Dick Willingale博士说。“我们预期X射线亮度将在本周末达到峰值。然后我们就能够估计撞击一共释放了多少彗星物质。”
[color=#DC143C]根据对X射线的初步分析,O';Brien估计被释放的物质多达数万吨,足够将宾州足球场掩埋到30英尺(10米)以下。观测和分析正在进行之中。
雨燕号为这次罕见的事件提供了唯一的多波段同时观测,观测窗口包括可见光,紫外线,X射线和伽玛射线。不同波长的光线揭示出彗星不同的秘密。
雨燕号小组希望可以将卫星在撞击后几小时内,收集到的紫外线数据与X射线数据进行比对。紫外线是由进入彗星低层大气层的物质所产生的;而X射线则来自于高层大气。
“这是第一次,我们能够目睹从彗星表面被释放的物质是如何迁移到它的上层大气层中的,”任务操控主管John Nousek教授说。“这将能提供关于彗星大气以及它与太阳风相互作用过程的美妙信息。这完全是个全新的领域。”
Nousek说,深度撞击与坦普尔1号彗星的相撞就像是一项受控的实验,模拟了火星上发生的、太阳风的缓慢蒸发过程。地球拥有一个磁场,能够保护我们不爱太阳风危害。火星在几十亿年前就丧失了磁场,太阳风剥离了这颗行星上的水份。
彗星与火星和金星一样,都没有磁场。彗星看起来如此巨大,是因为它在近距离经过太阳附近时,冰块从它们表面上蒸发出去。水被明亮的阳光离解成原子,并且被迅速移动的高能太阳风带离彗星。现在这种过程正在坦普尔1号彗星上迅速发生着,科学家们希望能够在几周内,而不是几十亿年内,研究这种蒸发过程。

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