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当前位置: Science » 生物物理 » Science:42小时一次的日食,木卫一冷到大气结霜


摘要 : 觉得你们那里的夜晚很凉快?对于木星最大的卫星之一:“伊俄”(Io,即木卫一)来说,当它每次绕转到木星背面的阴影中时,大气层就要冷到结霜和坍缩一次——在它每42小时一圈的公转周期里,这种现象都要持续2小时左右。


觉得你们那里的夜晚很凉快?对于木星最大的卫星之一:“伊俄”(Io,即木卫一)来说,当它每次绕转到木星背面的阴影中时,大气层就要冷到结霜和坍缩一次——在它每42小时一圈的公转周期里,这种现象都要持续2小时左右。最近,科学家们首次在远红外波段直接观测到了伊俄大气层的这种坍缩和恢复现象。如上图所示,伊俄的红色大气层极其稀薄,主要成分是火山喷发释放出的二氧化硫气体(图中蓝色喷泉状所示)。研究人员此前就曾提出,伊俄表面大气压只有地球表面的十亿分之一,在它转到木星背后并落入木星影子里(发生日食)时,其大气层中大部分二氧化硫气体会开始结成霜落到卫星表面,整个过程约2小时。然而由于日食发生时伊俄被遮蔽,很难在可见光波段看到其大气层,因此这种想法一直难以得到证实。现在有了大型地基望远镜的帮助,天文学家们得以在远红外波段观测伊俄(其表面产生的特定范围的辐射会被大气层中的二氧化硫吸收)。根据今天发表在《地球物理研究期刊E辑:行星》上的文章,当它从木星背后通过时,其表面温度会由127 开尔文(约零下146℃)骤降至105开尔文(约零下168℃),直接导致80%的大气凝结成霜。当日食结束、阳光再次降临到伊俄表面时,霜状的二氧化硫再升华成气态,重新回到大气层中。这一新发现有助于科学家们更好地研究木星系统的相关情况,因为伊俄火山喷发所释放的半数二氧化硫会最终漂移并散布到木星的周围。


Jupiter’s shadow turns Io’s atmosphere to frost once every 42 hours


Think your neck of the woods gets cold at night? On Io, one of Jupiter’s largest moons, the atmosphere turns to frost and collapses every time the orb passes into the planet’s shadow—for about 2 hours during each of the moon’s 42-hour orbits. Now, for the first time, scientists have observed the collapse—and recovery—of its atmosphere using far-infrared wavelengths. Io’s atmosphere (the reddish haze in the artist’s sketch, above), which is largely made of sulfur dioxide, originates from volcanic plumes scattered around the moon (depicted as blue fountains, above). Researchers had previously suggested that a substantial fraction of the tenuous shroud, which has a surface pressure about one-billionth that of Earth’s atmosphere at sea level, turns to frost for the 2 hours that Io lies in Jupiter’s shadow. But observations to prove the notion have been hard to come by, because the atmosphere can’t readily be seen at visible wavelengths when the moon is eclipsed. Now, astronomers have used a large ground-based telescope to observe the volcanic moon in far-infrared wavelengths, wher certain ranges of radiation from the moon’s surface get absorbed by the sulfur dioxide in the atmosphere. As Io passes behind Jupiter, its surface quickly cools from 127 K (–146°C) to about 105 K (–168°C), a sudden chill that’s sufficient to cause about 80% of the atmosphere to turn into frost, the researchers report online today in the Journal of Geophysical Research: Planets. Then, when the eclipse is over and sunshine returns, the sulfur dioxide frost evaporates back into a gas. The new findings may help scientists better understand the rest of the Jupiter system, wher about half the sulfur dioxide spewed from Io’s volcanoes eventually drifts to circulate around the planet.

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