行星地球面对面 危险近在咫尺？
<p><span word="A">A</span> <span word="mountain">mountain</span>-<span word="sized">sized</span> <span word="asteroid">asteroid</span> <span word="which">which</span> <span word="crosses">crosses</span> <span word="paths">paths</span> <span word="with">with</span> <span word="the">the</span> <span word="Earth">Earth</span> <span word="every">every</span> <span word="three">three</span> <span word="years">years</span> <span word="has">has</span> <span word="been">been</span> <span word="discovered">discovered</span> <span word="by">by</span> <span word="a">a</span> <span word="Russian">Russian</span> <span word="scientist">scientist</span>.</p><p>近日，一名俄罗斯科学家发现了一颗山峰大小的小行星每三年都会经过地球的运行轨道。</p><p><span word="Vladimir">Vladimir</span> <span word="Lipunov">Lipunov</span>, <span word="a">a</span> <span word="professor">professor</span> <span word="at">at</span> <span word="Moscow">Moscow</span> <span word="State">State</span> <span word="University">University</span>, <span word="said">said</span> <span word="the">the</span> <span word="space">space</span> <span word="rock">rock</span>, <span word="named">named</span> '2017 <span word="UR">UR</span>116', <span word="poses">poses</span> <span word="no">no</span> <span word="immediate">immediate</span> <span word="threat">threat</span>.</p><p>莫斯科国立大学（<span word="Moscow">Moscow</span> <span word="State">State</span> <span word="University">University</span>）教授弗拉基米尔（<span word="Vladimir">Vladimir</span> <span word="Lipunov">Lipunov</span>）表示，这颗名为“2017 <span word="UR">UR</span>116”的太空岩石目前对地球并未造成直接威胁。</p><p><span word="But">But</span> <span word="he">he</span> <span word="warned">warned</span> <span word="that">that</span> <span word="it">it</span> <span word="could">could</span> <span word="hit">hit</span> <span word="the">the</span> <span word="Earth">Earth</span> <span word="with">with</span> <span word="an">an</span> <span word="explosion">explosion</span> 1,000 <span word="times">times</span> <span word="greater">greater</span> <span word="than">than</span> <span word="the">the</span> <span word="surprise">surprise</span> 2013 <span word="impact">impact</span> <span word="of">of</span> <span word="a">a</span> <span word="bus">bus</span>-<span word="sized">sized</span> <span word="meteor">meteor</span> <span word="inRussia">inRussia</span>. <span word="That">That</span> <span word="object">object</span> <span word="entered">entered</span> <span word="Earth">Earth</span>’<span word="s">s</span> <span word="atmosphere">atmosphere</span> <span word="over">over</span> <span word="the">the</span> <span word="city">city</span> <span word="ofChelyabinsk">ofChelyabinsk</span>, <span word="resulting">resulting</span> <span word="in">in</span> <span word="a">a</span> <span word="series">series</span> <span word="of">of</span> <span word="ferocious">ferocious</span> <span word="blasts">blasts</span> <span word="that">that</span> <span word="blew">blew</span> <span word="out">out</span> <span word="windows">windows</span> <span word="and">and</span> <span word="damaged">damaged</span> <span word="buildings">buildings</span> <span word="for">for</span> <span word="miles">miles</span> <span word="around">around</span>.</p><p>但是，如果这颗小行星撞击地球，其产生的爆炸强度将会是2013年袭击俄罗斯的那颗公交车般大小的流星的1000倍。那颗流星穿越地球大气层，在车里雅宾斯克（<span word="Chelyabinsk">Chelyabinsk</span>）上空爆炸，火花四溅，击破了窗户，损坏了方圆数英里内的建筑。</p><p><span word="Prof">Prof</span> <span word="Lipunov">Lipunov</span> <span word="said">said</span> <span word="it">it</span> <span word="is">is</span> <span word="difficult">difficult</span> <span word="to">to</span> <span word="calculate">calculate</span> <span word="the">the</span> <span word="orbit">orbit</span> <span word="of">of</span> <span word="big">big</span> <span word="rocks">rocks</span> <span word="like">like</span> '2017 <span word="UR">UR</span>116' <span word="because">because</span> <span word="their">their</span> <span word="trajectories">trajectories</span> <span word="are">are</span> <span word="constantly">constantly</span> <span word="being">being</span> <span word="changed">changed</span> <span word="by">by</span> <span word="the">the</span> <span word="gravitational">gravitational</span> <span word="pull">pull</span> <span word="of">of</span> <span word="other">other</span> <span word="planets">planets</span></p><p>弗拉基米尔教授表示，像“2017 <span word="UR">UR</span>116”这类大型的石块常常会受到其他行星万有引力的影响，不停地改变其运行轨迹。因此，很难计算出它们的运行轨道。</p>
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