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[最新进展]深度撞击的烟尘比预想得更大!

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发表于 2005-7-12 13:32 | 显示全部楼层 |阅读模式
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Deep Impact';s Plume Was Bigger Than Expected

The huge plume of material shooting out of Comet Tempel 1. Image credit: NASA/JPL. Click to enlarge.
Data from Deep Impact';s instruments indicate an immense cloud of fine powdery material was released when the probe slammed into the nucleus of comet Tempel 1 at about 10 kilometers per second (6.3 miles per second or 23,000 miles per hour). The cloud indicated the comet is covered in the powdery stuff. The Deep Impact science team continues to wade through gigabytes of data collected during the July 4 encounter with the comet measuring 5-kilometers-wide by 11-kilometers-long (about 3-miles-wide by 7-miles-long).
"The major surprise was the opacity of the plume the impactor created and the light it gave off," said Deep Impact Principal Investigator Dr. Michael A';Hearn of the University of Maryland, College Park. "That suggests the dust excavated from the comet';s surface was extremely fine, more like talcum powder than beach sand. And the surface is definitely not what most people think of when they think of comets -- an ice cube."
How can a comet hurtling through our solar system be made of a substance with less strength than snow or even talcum powder?
"You have to think of it in the context of its environment," said Dr. Pete Schultz, Deep Impact scientist from Brown University, Providence, R.I. "This city-sized object is floating around in a vacuum. The only time it gets bothered is when the Sun cooks it a little or someone slams an 820-pound wakeup call at it at 23,000 miles per hour."
The data review process is not overlooking a single frame of approximately 4,500 images from the spacecraft';s three imaging cameras taken during the encounter.
"We are looking at everything from the last moments of the impactor to the final look-back images taken hours later, and everything in between," added A';Hearn. "Watching the last moments of the impactor';s life is remarkable. We can pick up such fine surface detail that objects that are only four meters in diameter can be made out. That is nearly a factor of 10 better than any previous comet mission."
The final moments of the impactor';s life were important, because they set the stage for all subsequent scientific findings. Knowing the location and angle the impactor slammed into the comet';s surface is the best place to start. Engineers have established the impactor took two not unexpected coma particle hits prior to impact. The impacts slewed the spacecraft';s camera for a few moments before the attitude control system could get it back on track. The penetrator hit at an approximately 25 degree oblique angle relative to the comet';s surface. That';s when the fireworks began.
The fireball of vaporized impactor and comet material shot skyward. It expanded rapidly above the impact site at approximately 5 kilometers per second (3.1 miles per second). The crater was just beginning to form. Scientists are still analyzing the data to determine the exact size of the crater. Scientists say the crater was at the large end of original expectations, which was from 50 to 250 meters (165 to 820 feet) wide.
Expectations for Deep Impact';s flyby spacecraft were exceeded during its close brush with the comet. The craft is more than 3.5 million kilometers (2.2 million miles) from Tempel 1 and opening the distance at approximately 37,000 kilometers per hour (23,000 miles per hour). The flyby spacecraft is undergoing a thorough checkout, and all systems appear to be in excellent operating condition.
The Deep Impact mission was implemented to provide a glimpse beneath the surface of a comet, where material from the solar system';s formation remains relatively unchanged. Mission scientists hoped the project would answer basic questions about the formation of the solar system by providing an in-depth picture of the nature and composition of comets.
The University of Maryland is responsible for overall Deep Impact mission science, and project management is handled by JPL. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation, Boulder, Colo. JPL is a division of the California Institute of Technology, Pasadena, Calif.
 楼主| 发表于 2005-7-12 13:46 | 显示全部楼层

[最新进展]深度撞击的烟尘比预想得更大!

大意:
深度撞击号传回的数据表明,探测弹头撞击彗星时,产生了一片由细腻粉末状物质组成的巨大尘埃云。这团尘埃云表明,彗星被一层粉末状物质所覆盖。
“最令人吃惊的是弹头溅起的烟尘的不简明度和它所发出的光线,”深度撞击首席研究员Michael A';Hearn博士说。“这意味着彗星表面溅起的尘埃是非常细腻的,更像是爽身粉,而不是沙滩上的沙子。并且表面上绝对没有大多数人们一提及彗星就会想到的东西——冰块。”
7月4日,深度撞击号弹头以每秒10公里的速度撞入彗核,入射弹道与彗星表面呈25度的倾角。被气化的弹头和彗星物质火球向上射出。它以大约每潲5公里的速度在撞击地点上方迅速膨胀。撞击坑开始形成 。科学家们仍然会继续分析数据,以测定撞击坑的确切大小。科学家们说撞击坑的大小可能偏向于最初预期范围的较大一侧。科学家们最初预期撞击坑的大小可能在50米到250米之间。

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