unenuitblanche周围记

11 October 2008
From New Scientist Print Edition. Subscribe and get 4 free issues.

    WHY are Saturn's rings so spectacular? It could be that the planet managed to cling onto a moon when all the other gas giants in our solar system had already lost theirs. Today's rings formed when the moon was smashed up.
    为什么土星的光环如此壮观?可能是因为在我们太阳系的其他气态巨星已经失去自己的卫星的时候,土星捕获了一个月亮.今天的光环就是当时那个月亮被搅碎的时候形成的.

    Sebastien Charnoz and colleagues at the University of Diderot, Paris, suggest it was during the "late heavy bombardment", 700 million years after Saturn formed, that a chunk of debris collided with one of the planet's moons. Because the moon was orbiting at just the right distance from Saturn when it shattered - within the so-called Roche limit - the tiny pieces formed the rings instead of dispersing.
    巴黎狄德罗大学的Sébastien Charnoz等人认为 在土星形成的7亿年后," 迟到的猛烈轰击"中一大块碎片与土星的其中一个月亮相撞.因为哪一个月亮当时刚好运行到土星引力最弱的一段距离----处于所谓的"洛希极限"----撞击留下的小碎片没有消失而是形成了土星的光环.

    This could explain why other planets don't have rings like Saturn's. Even if other planets had moons within their Roche limits at the birth of the solar system, the team's calculations show that the moons would soon been dragged down into the planet or unshackled from their orbits. Yet Saturn's rapid rotation meant it could hold a satellite within its Roche limit until the bombardment. The work will appear in the journal Icarus.
    这可以解释为什么其他星球没有像土星那样的光环.即使其他星球在太阳系诞生的时候有月亮在洛希极限距离上,研究小组的运算结果显示那些月亮会很快就被引力拖到星球上面去或者是从它们的轨道中脱离出去.然而,土星的高速自转意味着它能够在洛希极限中保持着一个卫星直到"猛烈轰击".研究将会在Icarus杂志上刊登.

    Ken Rice from the Institute of Astronomy in Edinburgh, UK, says the team's way of showing Saturn's uniqueness among gas giants is interesting, but that their hypothesis cannot be proved until we have better ways of modelling the evolution of the solar system.
    英国爱丁堡天文学研究所的Ken Rice说,研究小组展示土星在气态巨星中的唯一性的方式很有趣,但是在我们能更好地模拟出太阳系进化过程之前,他们的假设不能被证实.