[新闻] 卡西尼号发现土星光环新现象：电闪雷鸣(图)

　据外电报道，美国科学家8月5日称，“卡西尼”号太空船发现，在土星的大气层周围有一个新的光环，与美国宇航局“航行者”号在20世纪80年代早期发现的完全不同。

　　美国爱荷华大学比尔-库尔特教授称，接收“卡西尼”号无线电波和等离子波信号的设备发出了“噼噼啪啪”和“砰砰嚓嚓”爆裂声，就好像在雷鸣电闪时调幅收音机发出的声音一样。“‘卡西尼’发现的这些情况表明：在过去的20多年里，土星的雷电状况在发生变化。”库尔特说，其中的一个变化就是土星闪电的模式。

　　库尔特说，目前，“卡西尼”发现的闪电是零零星星的，时有时无--有时雷电交加，有时风平浪静；80年代早期，“航行者”发现的雷电模式却非常频繁。另外一个主要的不同之处是：“卡西尼”号发现的雷电围绕土星旋转一周的时间约10小时45分钟，比80年代早期的10小时5分钟长了一些。

　　科学家认为，“航行者”在80年代发现的雷电位于赤道附近，因而能够随着速度较快的赤道气流围绕土星高速旋转。“‘卡西尼’发现的雷电需要较长的时间是因为这些雷电所处的高度较高--因为高空气流移动的速度较慢。”库尔特说，因此，“卡西尼”发现的新光环位于土星的云层顶端。

　　光环是行星外部空间无形、均匀、圆环状区域，在这里有被行星磁场吸引的高能电子和离子。美国约翰斯-霍普金斯大学科学家G-米切尔称，从长远来看，光环对于行星大气层的变化、卫、以及围绕轨道运转的气体和尘埃起着极为重要的作用。“光环还影响着行星大气层上部的温度和化学成分。”(编译/江水）

 
　　来源： 新浪科技  2004-08-07 14:28


This artist concept shows how Cassini is able to detect radio signals from lightning on Saturn.

The Cassini spacecraft, which began its tour of the Saturn system just over a month ago, has detected lightning and a new radiation belt at Saturn, and a glow around the planet's largest moon, Titan.

The spacecraft's radio and plasma wave science instrument detected radio waves generated by lightning. "We are detecting the same crackle and pop one hears when listening to an AM radio broadcast during a thunderstorm," said Dr. Bill Kurth, deputy principal investigator on the radio and plasma wave instrument, University of Iowa, Iowa City. "These storms are dramatically different than those observed 20 years ago."

Cassini finds radio bursts from this lightning are highly episodic. There are large variations in the occurrence of lightning from day to day, sometimes with little or no lightning, suggesting a number of different, possibly short-lived storms at middle to high latitudes. Voyager observed lightning from an extended storm system at low latitudes, which lasted for months and appeared highly regular from one day to the next.

The difference in storm characteristics may be related to very different shadowing conditions in the 1980s than are found now. During the Voyager time period when lightning was first observed, the rings cast a very deep shadow near Saturn's equator. As a result, the atmosphere in a narrow band was permanently in shadow -- making it cold -- and located right next to the hottest area in Saturn's atmosphere. Turbulence between the hot and cold regions could have led to long-lived storms. However, during Cassini's approach and entry into Saturn's orbit, it is summer in the southern hemisphere and the ring shadow is distributed widely over a large portion of the northern hemisphere, so the hottest and coldest regions are far apart.

A major finding of the magnetospheric imaging instrument is the discovery of a new radiation belt just above Saturn's cloud tops, up to the inner edge of the D-ring. This is the first time that a new Saturnian radiation belt has been discovered with remote sensing.

This new radiation belt extends around the planet. It was detected by the emission of fast neutral atoms created as its magnetically trapped ions interact with gas clouds located planetward of the D-ring, the innermost of Saturn's rings. With this discovery, the radiation belts are shown to extend far closer to the planet than previously known.

"This new radiation belt had eluded detection by any of the spacecraft that previously visited Saturn. With its discovery we have seen something that we did not expect, that radiation belt particles can 'hop' over obstructions like Saturn's rings, without being absorbed by the rings in the process," said Dr. Donald G. Mitchell, instrument scientist for the magnetospheric imaging instrument at the Johns Hopkins University Applied Physics Laboratory, Laurel, Md.

Saturn's largest moon, Titan, is also shining for attention. Cassini's visual and infrared mapping spectrometer captured Titan glowing both day and night, powered by emissions from methane and carbon monoxide gases in the moon's extensive, thick atmosphere.

"Not only is Titan putting on a great light show but it is also teaching us more about its dense atmosphere," said Dr. Kevin Baines, science team member for the visual and infrared mapping spectrometer at JPL. "What is amazing is that the size of this glow or emission of gases is a sixth the diameter of the planet."

The Sun-illuminated fluorescent glow of methane throughout Titan's upper atmosphere ?revealing the atmosphere's immense thickness and extending more than 700 kilometers (435 miles) above the surface, was expected. However, the nighttime glow, persistently shining over the night side of Titan, initially surprised scientists.

"These images are as if you were seeing Titan through alien eyes. Titan glows throughout the near-infrared spectrum. If you were an alien it would be hard to get a good night's sleep on Titan because the light would always be on," said Baines.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter.

土星闪电的艺术想象图

不错!!!!！！