Photographer: Patrick Wiggins; Patrick's Web Site
Summary Author: Kurt Fisher; Patrick Wiggins
March 2010 Earth Science Picture of the Day Viewer's Choice
Most North Americans slept through the morning of January 13, 2010 as near-Earth object (NEO) 2010 AL30 silently moved across the night sky. Its path brought it to an altitude of about 122,000 km, which is one third of the distance to the Moon. 2010 AL30 is an asteroid approximately 10 to 15 m across. As shown above, Patrick Wiggins followed its passage using a 35 cm telescope and CCD camera. 2010 AL30 is estimated to be part of a NEO population of several thousand similar objects. On average, one 10-15 m diameter asteroid passes within one lunar distance of the Earth about once a week. If 2010 AL30 had entered the Earth's atmosphere, it would have created an air burst equivalent to between 50 kT and 100 kT (kilotons of TNT). The Nagasaki "Fat Man" atom bomb had a yield between 13-18kT.
On January 22, 2010, the National Research Council of the National Academy of the Sciences released its final report as requested by the United States Congress. This report recommended an optimal approach to complete the census of NEOs larger than about 140 m as well as an optimal approach for deflecting a NEO that threatens impact with the Earth. The report recommended that the census of NEOs be expanded to include NEOs between 30 and 50 m in diameter. NASA's NEO program estimates that "with an average interval of about 100 years, rocky or iron asteroids larger than about 164 ft (50 m) would be expected to reach the Earth's surface and cause local disasters or produce the tidal waves that can inundate low lying coastal areas." A NEO with a diameter of 50 m can create a blast equivalent to one megaton of TNT.
There have not been a significant number of deaths caused by asteroids in historical times due to the infrequency of the major events. When such events do occur they are more likely to happen over unpopulated regions such as oceans. Noting that without better surveys, accurate estimates of the risk of NEO impacts cannot be made, the report made best current estimates for the global risk of death by shark at 3-7 persons per year, death by asteroid at 91 persons per year and death by automobile at 1,200,000 persons per year.
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