新闻：首度直接拍摄到彗星轨道上的流星体尾迹照片[图文][英汉]
来自Spitzer望远镜主页。Argo Navis翻译:P
NASA/Jpl-Caltech
严禁用于商业用途！
These images of the Jupiter-family comets Johnson (top) and Shoemaker-Levy 3 (bottom) were both taken with Spitzer's multiband imaging photometer (MIPS) at a wavelength of 24 microns.
这两张木星族彗星——Johnson（上）和Shoemaker-Levy 3（下）——的照片都是用Spitzer空间望远镜的宽频成像光度计MIPS（？）在24微米波段上拍摄的。
The fan-shaped region that stretches upward from Johnson's nucleus (yellow ball in the middle) represents the dust "tail" of the comet. Dust tails are created when small particles from a comet are swept backward by the Sun's radiation pressure.
从Johnson彗星的彗核（照片中部的黄色球体）向上延展的扇状区域描绘出了这颗彗星的尘埃“尾”。来自彗星的微小粒子被太阳辐射压向后推斥，形成尘埃尾。
The image of Shoemaker-Levy 3 (bottom) does not show a dust tail.
Shoemaker-Levy 3 的照片上没有显示出尘埃尾。
In both images the long thin trail of emission that precisely follows the orbit of the comet is believed to be a debris trail of solid material, ranging from millimeters to centimeters in size. Such particles, called meteoroids, are the same size as those that appear in meteor showers when they enter the Earth's atmosphere. Because any trace of water would evaporate in the Sun's heat, astronomers do not believe that debris trails contain ice.
在两张照片上都出现了细长的喷射状尾迹，恰好与彗星的轨道重合。这种尾迹被认为是固态的残片，大小在毫米级到厘米级。这些被称为“流星体”的微粒，和在流星雨时落入地球大气的流星具有同样的大小。由于水在太阳辐射下会汽化，天文学家们认为这里的尾迹并不含有冰。
These meteoroids have evaded detection in previous comet images because they are relatively faint in visible light. At mid-infrared wavelengths, meteoroids give off infrared radiation. Any object with an internal temperature higher than absolute zero (-273.5 degrees Celsius or zero Kelvin) produces thermal radiation; objects in the inner solar system give off radiation at mid-infrared wavelengths. Consequently, MIPS allows astronomers to study the production of meteoroids by comets whose orbits do not cross the Earth's path.
这些彗星轨道上的流星体以前从未在照片上被发现，因为它们在可见光波段相对黯淡一些，而在中红外波段，流星体发出辐射。任何温度高于绝对零度的物体都会产生热辐射，内太阳系的天体就有中红外线辐射。因此，MIPS使天文学家得以研究与地球轨道不交汇的彗星产生的流星体。
Spitzer images have also shown that there is more mass in the debris trails of comets than in their dust tails and gases.
Spitzer望远镜的照片还显示，彗星的残片尾迹比尘埃尾和气体尾包含更多的质量。
The results of Spitzer's observations are consistent with those obtained by space probes that encountered comet Halley in 1986. In Halley's case, large particles produced by the comet were not only detected, but caused significant damage to the probes.
Spitzer望远镜的观测结果与1986年同Halley彗星会合的探测器得到的结果一致。在Halley彗星的例子中，彗星产生的大颗粒不仅仅被探测到了，还对探测器造成了严重损害。
图片
http://ipac.jpl.nasa.gov/media_images/sig05-008_medium.jpg 我认为这组照片意义还是比较重大的。我们根据对流星雨和彗星的观测，间接推断彗星和流星群的关系；而这两颗彗星的轨道与地球轨道是不交汇的，假设它们的确产生流星群，也不可能在地球上观测到流星雨。在这样的情况下，我们直接看到了彗星轨道上的流星群，这是一条有力的、直接的证据，进一步确认了现在的流星群模型的正确。
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