小行星和地球相撞或使人类过上“吸血鬼”生活

　　An asteroid splashdown in one of Earth's oceans could trigger adestructive chemical cycle that would wipe out half of the ozone layer,according to a new study. The massive loss of protection against thesun's ultraviolet (UV) radiation would likely force humans into avampire-style existence of staying indoors during daylight hours。

　　The worst scenario based on an asteroid 1 kilometer wide wouldre-create the hole in the ozone layer, which appeared over Antarcticaduring the 1990s, except this would be worldwide. UV levels in thestudy's simulation soared beyond anything measured so far on Earth bythe UV Index's daily forecasts of overexposure to UV radiation, andremained that way for as long as two years。

　　Researchers tested scenarios with a 0.6-mile asteroid and a0.3-mile asteroid (500 meters) at a specific location and specific timeof year. Models used in the research showed how ozone destruction wouldresult from an asteroid strike launching seawater vapor hundreds ofmiles up into the highest parts of the atmosphere. Chemical elementssuch as chloride and bromide that separated from the water vapor couldthen wreak havoc by destroying the ozone layer that protects life onEarth from UV rays。

　　Long-term effects of such high UV radiation would includeskin-reddening, changes in plant growth and genetic mutations for humansand other organisms. And an asteroid has about twice the chance ofstriking water rather than hitting land. Those odds come from the factthat over 70 percent of the Earth's surface is covered by water。

　　Asteroid hunters have found about 903 of an estimated 1,050near-Earth objects (NEOs) with diameters of 1 kilometer or greater as ofOctober 1. That still leaves well over 100 objects in the 1-2 kilometersize undiscovered。

　　美国“趣味科学”网站26日报道称，最新科学研究显示，小行星坠入地球海洋会引发毁灭性的化学连锁反应，导致50%的臭氧层消失。缺少了臭氧层对太阳紫外线辐射的抵挡，人类将有可能被迫过起“吸血鬼”般的生活——白天只能躲在屋子里。

　　早在上世纪90年代，南极洲上空就已出现臭氧空洞。此次研究发现，直径达1000米的小行星撞击地球后也会出现臭氧空洞，且危害波及整个地球。研究结果显示，模拟太阳紫外线辐射在撞击后飙升，超过了此前在地球上测量的所有紫外线辐射指数预报数据，并且会以这种状态保持两年。

　　在实验中，研究人员测试了特定时间特定地点下直径分别为1000米和500米的小行星。研究人员通过观察模型发现了小行星坠落入地球海洋后的臭氧层破灭过程：巨大的撞击力量使得海水蒸汽上升至大气层最高点，随后氯化物及溴化物等化学物质脱离水汽，毁坏保护人类免受辐射的臭氧层。

　　据悉，长期面临辐射可导致皮肤红化、植物生长发生改变、人类以及其他有机体的基因变异。而且据了解，小行星落入海洋的几率是与陆地相撞几率的两倍，原因在于地球70%以上的表面被水覆盖。

　　据估计，截至10月初，直径大于等于1000米的近地小行星约有1050个，行星探测器已发现903个，而还有100多个直径为1000到2000米的小行星尚待发掘。