The world needs to sharpen up its asteroid alerting capabilities, say scientists, following the massive asteroid airburst over the Yukon in northern Canada earlier this year (www.space.com/scienceastronomy/astronomy/classified_impacts_000502. html). The blast, which took place 16 kilometres above the Earth, was equivalent to a four-thousand-tonne bomb going off and was bright enough to turn street lights off.
Just as earthquakes have the Richter scale, there's a scale that measures the severity of asteroid impacts. Called the Torino scale, it ranges from 0 for a near miss to 10 for a global climate catastrophe (http://impact.arc.nasa.gov/torino/index.html). Reassuringly, the greater the destruction of an impact, the less frequently it occurs: there's been a 10 roughly every 100 000 years. For a fascinating examination of the threatsóand many proposed countermeasuresólook up the proceedings of the 1995 Planetary Defense Workshop at www.llnl. gov/planetary, to which the late, great comet hunter Eugene Shoemaker made many contributions.
Just for fun, you can simulate your very own catastrophic strike at http://janus.astro.umd.edu/astro/impact/. Choose the size, velocity and type of meteorite or asteroid, select a planetary target and hit the "kaboom" button. The site then calculates how much damage your strike caused, the size of the crater, its depth, and the scale of the ensuing earthquake. Having discovered the damage an asteroid can do, you'll want to take out some insurance from www.ufo2001.com/asteroid.htm. "Don't get hit without it," runs the ad.
If you're still unconvinced of the threat, check out http://gdcinfo.agg.emr.ca/toc.html?/crater/world_craters. html for an idea of the number of large meteorites that have actually hit this planet. You can tour the world and zoom in on impact structures to learn how they were formed. Me? I'm off to buy a meteor-proof baseball hat . . .
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