The end is near... well, in 7.6 billion years

末日来临——就剩76亿年啦


The big news: Earth is doomed to fry and then be gobbled up by the dying Sun. But don’t blow your savings on an Apocalypse Party just yet, for astronomers say the planet’s demise is 7.6 billion years away.

特大新闻：地球注定要被烤焦，然后被燃烧殆尽的太阳吞没。但是先别把存款在末日晚会上都挥霍了，因为天文学家说离地球毁灭还有76亿年哪。

Robert Smith, emeritus reader in astronomy at the University of Sussex, southern England, previously calculated that as the Sun runs out of fuel, it will expand into a dangerous “red giant”. But Earth—while battered and burnt to a crisp—would escape ultimate destruction, he had thought. Smith, working with Klaus-Peter Schroeder at the University of Guanajuato in Mexico, has taken a new run through the figures. Sadly, for our home, the number is up. “The tenuous outer atmosphere of the Sun extends a long way beyond its visible surface, and it turns out the Earth would actually be orbiting within these very low-density outer layers,” Smith says. “The drag caused by this low-density gas is enough to cause the Earth to drift inwards, and finally to be captured and vaporised by the Sun.” Life on Earth will have become rather uncomfortable before then, however. A billion years from now, as the Sun slowly expands, the oceans will evaporate, filling the atmosphere with water vapour (a potent greenhouse gas) and triggering runaway global warming.

罗伯特•史密斯是英格兰南部苏塞克斯大学天文系的荣誉高级讲师，他曾经测算，当太阳燃尽时，会膨胀成一个危险的“红色巨无霸”。他原本认为伤痕累累并被烤干的地球会逃过这最后一劫。如今史密斯与墨西哥瓜纳华托大学的克劳斯-彼得•施罗德合作，重新演算了一遍数据。惨的是，对我们的家园来说，这个数字临近了。“稀薄的太阳外部大气层伸延到太阳表面以外很长，结果地球正在这些低密度的大气层之内旋转。”史密斯说。“由这个低密度大气所产生的引力足够使地球向内漂移，最终被太阳捕获，然后蒸发。”然而在此之前地球上的生命会相当难受哇。从现在起10亿年之后，当太阳渐渐膨胀时，海洋将会蒸发，使地球大气层充满水蒸气（一种潜在的温室气体），引起全球变暖失控。

Smith sketches two options, both admittedly sci-fi in feel, for escaping this fate. One is to harness the gravitational pull of a passing asteroid to gently tug Earth out of the danger zone. A wee nudge every 6,000 years could be enough to survive for at least five billion years—provided a miscalculation does not send the asteroid barrelling into Earth, says Smith. “A safer solution may be to build a fleet of interplanetary ‘life rafts’ that could manoeuvre themselves always out of reach of the Sun but close enough to use its energy,” he says.

史密斯草拟了两个方案来避免这个命运，显然，感觉起来两个都像科幻小说。第一个是利用经过地球的小行星的吸引力，轻轻地将地球拉到危险地带之外。每6,000年一次的轻轻一推至少够地球存活50亿年——假设计算失误没有让小行星撞到地球上，史密斯是这么说的。“更安全的做法是打造一支星际‘救生艇’舰队，能一直游弋在太阳所及之外，但又能离得足够近，利用太阳的能量。”他说。

Remarks: 时不我待！离地球毁灭就剩76亿年了，让我们早做准备吧。

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