Asteroid Headed for Earth

Astronomers are tracking an asteroid, at least 1 kilometer wide, that could hit Earth in 2028. The orbit of the massive asteroid, known as 1997 XF11, was posted today on the Internet by the International Astronomical Union. At about 1:30 p.m. Eastern time on 26 October 2028, the chunk of rock will almost certainly pass closer to Earth than the moon.

But don't bet on Armageddon, observers say. The chance of the asteroid striking Earth "can't be greater than about 1%, probably less," says Alan Harris of the Jet Propulsion Laboratory in Pasadena, California. The current estimate, calculated by Brian Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, is based on only a fraction of the object's orbit. The announcement urges other astronomers to train their sights on the object over the next few weeks, before it fades into the dusk.

The asteroid is bright enough that powerful telescopes can observe most of its trip around the sun, but after late March, the best chances to make careful observations will be in early 2000 and on Halloween 2002--when the asteroid passes to within 10 million km of Earth. By then, Harris says, "we will have the chance to nail this orbit down to a gnat's eyebrow." At that point, he says, astronomers might be able to predict the asteroid's point of impact--if it were to strike Earth--to within a few hundred kilometers. An asteroid of that size that struck Earth would not only wipe out any nearby real estate, but could also kick up as much dust as the planet's largest volcanoes, Harris says.

Sky watchers are thrilled by the find. If the current estimate is correct, the asteroid will shine as brightly as some of the brightest stars as it moves across the sky over the course of a few hours in 2028. "It's the most interesting case that we've ever had by a long way," says Ted Bowell of Lowell Observatory in Flagstaff, Arizona. He says there have been several instances of large asteroids passing closer than the moon, but none of them as big as this one.