Friday, April 18th, 2008

Apophis ad Absurdum

At some point you’ve probably been driving down the freeway and had a bug hit your windshield.   Did the impact send you careening off the side of the road? I thought not. But that’s the underlying premise of a ridiculous story that took the Internet by storm yesterday.

On Friday the 13th in April 2029, a 1,000-foot-wide asteroid named Apophis will pass close enough to Earth (within 20,000 miles) to briefly appear as a 3rd-magnitude star in the night sky.

Dan Durda

It seems that a 13-year-old German student chose a study of near-Earth asteroids for his entry in a prestigious science-fair competition. While crunching the numbers for a 1,000-foot-wide asteroid named 99942 Apophis, he discovered that the giant rock might strike an orbiting satellite when it brushes within 18,000 to 20,000 miles of Earth on April 13, 2029.

That possibility, the student concluded, had been overlooked by NASA’s top dynamicists, and it increased the chance of Apophis crashing into Earth itself on a subsequent pass in 2036 from 1 in 45,000 (NASA’s estimate) to just 1 in 450. It’s a harrowing prospect — if he had actually been correct.

The story first appeared on April 4th in Bild, the German equivalent of Weekly World News. “I have calculated the end of the world!” screams the headline “…and NASA says, I’m right.” This silliness might have died quietly, had the Agence France-Presse not repeated and embellished the tale on April 15th.

Kudos to German science writer Daniel Fischer, who got to the bottom of this mess and yesterday exposed it for the farce (or hoax) it was.

First, the boy misunderstood the flyby geometry in 2029 — the chance of striking a satellite is “vanishingly unlikely,” NASA scientists insist. While it’s true that Apophis will pass closer than the altitude of geosynchronous satellites, it’ll be well outside them when it crosses Earth’s equatorial plane, where they’re located.

Second, Apophis has an estimated mass of some 20 million tons. Even if it did have a head-on collision with a sizable satellite, the impact would barely affect the asteroid’s trajectory. (If you don’t believe me, just ask the bug.)

Posted by Kelly Beatty, April 17, 2008