研究：35亿年后金星可能撞地球[文章来自:考试与评价 "=|D0b+ObHr:_fOt]
Earth-Venus smash-up possible in 3.5 billion years: study[文章版权 禁止转载:考试与评价 S_"nZKr&Jxo^ZOhFroG]
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最新一期英国《自然》期刊上的研究报告称，一种叫做“轨道混沌”的力量可能致使地球与金星、火星等相撞，从而引发太阳系混乱。不过，这种混乱出现几率约为1/2500，且在35亿年内不会发生。上述研究结果是巴黎检测中心研究人员使用计算机数字模拟技术，对未来50亿年太阳系星球轨道不稳定性进行了上百次模拟实验后得出的。[文章版权 禁止转载:考试与评价 k^4!=A4OBrDB"LiT FroG]
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A force known as orbital chaos may cause our Solar System to go haywire, leading to possible collision between Earth and Venus or Mars, according to a study released Wednesday.
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The good news is that the likelihood of such a smash-up is small, around one-in-2500.
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And even if the planets did careen into one another, it would not happen before another 3.5 billion years.
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Indeed, there is a 99 percent chance that the Sun's posse of planets will continue to circle in an orderly pattern throughout the expected life span of our life-giving star, another five billion years, the study found.
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After that, the Sun will likely expand into a red giant, engulfing Earth and its other inner planets -- Mercury, Venus and Mars -- in the process.
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Astronomers have long been able to calculate the movement of planets with great accuracy hundreds, even thousands of years in advance. This is how eclipses have been predicted.
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But peering further into the future of celestial mechanics with exactitude is still beyond our reach, said Jacques Laskar, a researcher at the Observatoire de Paris and lead author of the study.
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"The most precise long-term solutions for the orbital motion of the Solar System are not valid over more than a few tens of millions of years," he said in an interview.
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Using powerful computers, Laskar and colleague Mickael Gastineau generated numerical simulations of orbital instability over the next five billion years.
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Unlike previous models, they took into account Albert Einstein's theory of general relativity. Over a short time span, this made little difference, but over the long haul it resulted in dramatically different orbital paths.
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The researchers looked at 2,501 possible scenarios, 25 of which ended with a severely disrupted Solar System.
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"There is one scenario in which Mars passes very close to Earth," 794 kilometres (493 miles) to be exact, said Laskar.
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"When you come that close, it is almost the same as a collision because the planets gets torn apart."
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Life on Earth, if there still were any, would almost certainly cease to exist.
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To get a more fine-grained view of how this might unfold, Laskar and Gastineau ran an additional two hundred computer models, slightly changing the path of Mars each time.
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All but five of them ended in a two-way collision involving the Sun, Earth, Mercury, Venus or Mars. A quarter of them saw Earth smashed to pieces.
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The key to all the scenarios of extreme orbital chaos was the rock closest to the Sun, found the study, published in the British journal Nature.
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"Mercury is the trigger, and would be be the first planet to be destabilised because it has the smallest mass," explained Laskar.
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At some point Mercury's orbit would get into resonance with that of Jupiter, throwing the smaller orb even more out of kilter, he said.
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Once this happens, the so-called "angular momentum" from the much larger Jupiter would wreak havoc on the other inner planets' orbits too.
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"The simulations indicate that Mercury, in spite of its diminutive size, poses the greatest risk to our present order," noted University of California scientists Gregory Laughlin in a commentary, also published in Nature.
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