Friday the 13th, 2029
Friday the 13th is supposed to be an unlucky day, the sort of day you trip on your shoe laces or lose your wallet or get bad news.
But maybe it's not so bad. Consider this: On April 13th--Friday the 13th--2029, millions of people are going to go outside, look up and marvel at their good luck. A point of light will be gliding across the sky, faster than many satellites, brighter than most stars.
What's so lucky about that? It's asteroid 2004 MN4 ... not hitting Earth.
see captionFor a while astronomers thought it might. On Christmas Eve 2004, Paul Chodas, Steve Chesley and Don Yeomans at NASA's Near Earth Object Program office calculated a 1-in-60 chance that 2004 MN4 would collide with Earth. Impact date: April 13, 2029.
Asteroid 2004 MN4 had been discovered in June 2004, lost, then discovered again six months later. With such sparse tracking data it was difficult to say, precisely, where the asteroid would go. A collision with Earth was theoretically possible. "We weren't too worried," Chodas says, "but the odds were disturbing."
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This is typical, by the way, of newly-discovered asteroids. Step 1: An asteroid is discovered. Step 2: Uncertain orbits are calculated from spotty tracking data. Step 3: Possible Earth impacts are noted. Step 4: Astronomers watch the asteroid for a while, then realize that it's going to miss our planet.
Astronomers knew 2004 MN4 would miss Earth when they found pictures of the asteroid taken, unwittingly, in March 2004, three months before its official discovery. The extra data ruled out a collision in 2029.
Instead, what we're going to have is an eye-popping close encounter:
On April 13, 2029, asteroid 2004 MN4 will fly past Earth only 18,600 miles (30,000 km) above the ground. For comparison, geosynchronous satellites orbit at 22,300 miles (36,000 km). "At closest approach, the asteroid will shine like a 3rd magnitude star, visible to the unaided eye from Africa, Europe and Asia--even through city lights," says Jon Giorgini of JPL. This is rare. "Close approaches by objects as large as 2004 MN4 are currently thought to occur at 1000-year intervals, on average."
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