we no longer possess a rocket powerful enough to send humans even as far as the Moon. 我们不再拥有能把人送上月球的火箭。

　　The last rocket that could, Saturn 5, was retired years ago and has never been replaced. 最后一枚那种火箭——木星5型火箭——已于几年前退役，再也没有替身。

　　Nor could we quickly build a new one because, 我们也无法马上制造一枚，因为

　　amazingly, the plans for Saturn launchers were destroyed as part of a NASA housecleaning exercise. 木星火箭的图纸已经令人吃惊地在美国国家航空和航天局的一次春季大扫除中给销毁了。

　　Even if we did manage somehow to get a warhead to the asteroid and blasted it to pieces, 即使我们成功地设法将一枚弹头射中小行星并把它炸得粉碎，

　　the chances are that we would simply turn it into a string of rocks 我们很可能只能把它变成一连串岩石；

　　that would slam into us one after the other in the manner of Comet Shoemaker-Levy on Jupiter, 那些岩石会像苏梅克-列维彗星撞击木星那样一个接一个地朝我们砸过来，

　　but with the difference that now the rocks would be intensely radioactive. 不同之处在于那些岩石现在都具有强烈的辐射作用。

　　Tom Gehrels, an asteroid hunter at the University of Arizona, 亚利桑那大学负责寻找小行星的汤姆·格雷尔斯认为，

　　thinks that even a year's warning would probably be insufficient to take appropriate action. 即使有一年的预警时间也很可能不足以采取适当的行动。

　　The greater likelihood, however, is that we wouldn't see any object, even a comet, 然而，更大的可能性是，我们看不到任何物体，即使是彗星，

　　until it was about six months away, which would be much too late. 直到只剩下6个月左右时间，那时候就太晚了。

　　Shoemaker-Levy 9 had been orbiting Jupiter in a fairly conspicuous manner since 1929, but it took over half a century before anyone noticed. 自1929年以来，苏梅克-列维9号彗星一直在以比较明显的方式绕着木星运行，但直到半个多世纪以后才有人发现。

　　Interestingly, because these things are so difficult to compute and must incorporate such a significant margin of error, 由于这类事情很难测算，而且必须考虑这么大的误差，

　　even if we knew an object was heading our way we wouldn't know until nearly the end, 因此即使我们知道有个物体在朝我们飞来，也要等到差不多最后时刻，

　　the last couple of weeks anyway—whether collision was certain.  反正是最后几个星期——我们才会知道是不是肯定要发生撞击。