保卫地球——近地天体的巡视与防御陨击的对策

地球处于危险的宇宙环境中。运行到地球附近的"近地天体(NEO)"潜在着撞击地球的危险。实际上,地球自诞生以来就不断地受到这些天体的轰击,月球和水星的斑痕累累陨击坑就是最好的佐证,只是地球经历严重演化而抹去了老的陨击遗迹,仅见到170多个较近期的陨击构造。幸运的是,现阶段的陨击大多是规模小的,危害不太大。然而,陨击是很难预料的,一旦发生较大的撞击,就会造成比大地震还严重得多的危害。1994年的彗星撞击木星事件轰动世界,启迪人们更加关注地球被撞击的危险问题。实际上,也不乏地球近期遭遇陨击的例子:1908年的通古斯爆炸事件;1976年的吉林陨石雨;2008年的小行星2008TC3陨落在苏丹。2010年初,美国科学院公布《保卫地球:近地天体巡天和缓解危险策略最终报告》,笔者将结合有关资料作简要介绍,让公众了解真实的科学知识和对策,以免被歪曲的影视情节所误导。

Defending Planet Earth:Near-Earth Object Surveys and Hazard Mitigation Strategies

The earth inhabits a hazardous environment. “Near Earth Objects（NEO）”，whose orbits approach Earth’s orbit, could pose potential hazard of striking Earth. In fact, since its birth, the earth is continually bombarded by these objects. The scarred countless impact craters from Moon and Mercury are the best evidence. Because of a serious evolution of the Earth and the remains of the old impact craters being wiped out, only more than 170 impact structures are identified. Fortunately, the impacts from the objects at this stage are mostly in small scale , their hazards are not too serious. However, an impact event is difficult to predict. Once the event of a larger impact occurs, they will result in much more serious than the big earthquake hazards. The event of the comet colliding with Jupiter in 1994 shocked the whole world, and enlightened people to pay more attention to the dangers of the earth by such impact. In fact, there are some recent examples：Tunguska explosion event in 1908; the Jilin meteorite shower in 1976; the asteroid 2008 TC3 fallen in Sudan in 2008. Earlier 2010, the U.S. Academy of Sciences announced, “defend the Earth: near earth objects survey and mitigation of risk strategy for the final report”. Combined with relevant information，the real scientific knowledge and mitigation of risk strategy are introduced briefly to the public understanding and to avoid seriously misleading from the distorted video.