Impact Risks for Earth

Written by The Night Sky Guy on July 28, 2009 – 3:47 pm -

With Jupiter just being smacked again by a potential comet or asteroid, the media are abuzz once more with the discussion of our own planet being in danger from a doomsday rock from space. What exactly are the risks?  Space.com ran an interesting story today where astronomer Donald Yeomans, manager of NASA’s Near-Earth Object program office at the Jet Propulsion Laboratory, was asked how well we were doing in tracking down wayward asteroids that may have Earth in their cross-hairs.  Turns out that its the highrise-sized boulders, not the giant, city-sized dino-killers that we need to possibly watch out for in the short-term, ie. in our lifetime.

“Researchers suspect about 156 large NEOs 1 kilometer in diameter or larger remain to be found, and when it comes to dangerous NEOs in general, “when we get down to 140 meters (460 feet) or larger diameter objects, we think we’ve discovered about 15 percent of them, and with 50 meters (164 feet) or larger diameter, we’ve discovered less than 5 percent of them,” Yeomans explained.

On average, an NEO roughly a half-mile wide or larger hits the Earth roughly every 500,000 years, “so we’re not expecting one anytime soon,” Yeomans explained.

“For 500 meters (1,640 feet), we’re talking a mean interval of about 100,000 years,” he added. “When you get down to 50 meters, the mean interval is about 700 years, and for 30 meters (98 feet), about 140 years or so, but by then you’re getting down to a size where you won’t expect any ground damage, as they burn up in the atmosphere at about 25 meters (82 feet) in diameter and smaller, probably for an impressive fireball event.”"

I am not sure that all of them would burn up in the atmosphere at those sizes however. There have recently been much talk in the science community that even air bursts of building sized rocks, if they are solid enough can produce extensive local damage. There is still way too much speculation going on without any definite answers as to what the real dangers are. Hopefully cosmic impact events like this past week and the resulting chatter will result in more vigorous research into this field. After all, our life may depend on it. 


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