Brown P, Spalding R E, ReVelle D O, Tagliaferri E, Worden S P
Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 3K7, Canada.
Nature. 2002 Nov 21;420(6913):294-6. doi: 10.1038/nature01238.
Asteroids with diameters smaller than approximately 50-100 m that collide with the Earth usually do not hit the ground as a single body; rather, they detonate in the atmosphere. These small objects can still cause considerable damage, such as occurred near Tunguska, Siberia, in 1908. The flux of small bodies is poorly constrained, however, in part because ground-based observational searches pursue strategies that lead them preferentially to find larger objects. A Tunguska-class event-the energy of which we take to be equivalent to 10 megatons of TNT-was previously estimated to occur every 200-300 years, with the largest annual airburst calculated to be approximately 20 kilotons (kton) TNT equivalent (ref. 4). Here we report satellite records of bolide detonations in the atmosphere over the past 8.5 years. We find that the flux of objects in the 1-10-m size range has the same power-law distribution as bodies with diameters >50 m. From this we estimate that the Earth is hit on average annually by an object with approximately 5 kton equivalent energy, and that Tunguska-like events occur about once every 1,000 years.
直径小于约50 - 100米的小行星与地球碰撞时，通常不会以单个天体的形式撞击地面；相反，它们会在大气层中爆炸。这些小天体仍然可能造成相当大的破坏，比如1908年发生在西伯利亚通古斯卡附近的事件。然而，小天体的通量受到的限制很大，部分原因是地面观测搜索所采用的策略使它们优先发现较大的天体。此前估计，类似通古斯卡级别的事件——其能量我们认为相当于1000万吨TNT——每200 - 300年发生一次，计算得出的每年最大空中爆炸能量约为20千吨TNT当量（参考文献4）。在此，我们报告过去8.5年大气层中火流星爆炸的卫星记录。我们发现，直径在1 - 10米范围内的天体通量与直径大于50米的天体具有相同的幂律分布。据此我们估计，地球平均每年会受到一个能量约为5千吨当量的天体撞击，类似通古斯卡的事件大约每1000年发生一次。
