新托福阅读训练：Saturn’sinfraredauroralglow,madecolorful

土星，是太阳系中的重要一员，体积仅次于木星。人类正在苦苦探索这个庞大而陌生的星球，美国的卡西尼土星探测飞船就给我们带来了许多新鲜的信息。

 

　　Majestic, ringed Saturn little resembles the relatively tiny blue marble that is Earth, but the massive gas giant planet is home to at least one phenomenon that would be familiar to high-latitude dwellers here on Earth. Although the underlying mechanisms may differ somewhat, Saturn has northern and southern lights at its poles, just as Earth does.

　　Auroras arise when charged particles are funneled along converging magnetic field lines and into the upper atmosphere at the poles. At Earth, the effect is dominated by the solar wind; at Saturn a complex mixture of other geomagnetic phenomena appear to contribute as well. Charged particles striking Saturn's upper atmosphere ionize hydrogen atoms and produce infrared radiation, whereas related processes also give off Saturnian auroras at ultraviolet and radio wavelengths.

 

　　The infrared auroras show up in green in this false-color composite from NASA's Cassini spacecraft, stitched together from 65 individual observations taken by the probe's Visual and Infrared Mapping Spectrometer in 2008. According to a NASA news release, the auroral light appears in the near infrared at wavelengths of three to four microns. Blue designates reflected sunlight at two microns, and red represents thermal emissions at five microns.