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. Last Updated: 07/27/2016

Earth to See Near Miss From Orbiting Asteroid

WASHINGTON -- Humanity will dodge a bullet from space Friday as an itinerant asteroid named Toutatis passes within 5.3 million kilometers of Earth, a close call by astronomical standards.

But in the solar system, what goes around comes around. And in the case of Toutatis, it will be back. The rocky object -- almost 5 kilometers long, 2.5 kilometers wide and shaped like a sort of mutant carrot -- has an orbit that brings it near Earth every four years.

In 1992, Toutatis came within about 2 million miles of Earth. On Sept. 29 in 2004, it will swoop less than 1 million miles away, only four times the distance to the moon, according to Gareth Williams of the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.

Such ballistic debris (either leftover rubble from planet formation or the cores of comets that ran out of gas in our neighborhood) is disconcertingly common. Astronomers estimate there may be 1,000 to 10,000 objects with a diameter of one-quarter mile or larger that have orbits that bring them close to Earth. The first such "near-Earth asteroid,'' or NEA, was discovered in 1918, and by 1982 the total had increased to 49. In the next 10 years, an additional 110 were found, radio astronomer Gerrit Verschuur writes in his new book, "Impact!''

The official NEA count is now 391, of which 205 cross Earth's orbit. That number keeps growing, said Lucy McFadden, a planetary scientist at the University of Maryland, because "we now have about eight programs worldwide with telescopes scanning the skies to find those (near-Earth objects) we don't know about already.''

Asteroids like Toutatis -- as well as comets that approach close to Earth -- have become a matter of urgent interest because the odds are good that, within a few centuries, the planet will be struck by a sizable object.

In 1993, a specially commissioned NASA panel estimated that there is approximately a 1-in-10,000 chance that the Earth will be whacked by something one-third of a mile in diameter or greater within 100 years. Many scientists now believe that the extinction of the dinosaurs some 65 million years ago was caused by catastrophic climate change resulting from the impact of an object at least 6 miles in diameter that struck what is now the Yucatan peninsula in Mexico.