updated 3/2/2009 4:34:54 PM ET 2009-03-02T21:34:54

An asteroid the size of a 10-story building flew past Earth today about twice the distance as the highest Earth-orbiting satellites.

The space rock was about 115 feet (35 meters) wide, perhaps a bit larger than one thought to have created a colossal explosion in the air above Siberia in 1908 that flattened 500,000 acres (2,000 square kilometers) of forest.

Asteroid 2009 DD45 was closest to Earth today at about 8:40 a.m. ET. It was some 44,740 miles (72,000 km) away. That's twice the height of a geostationary communications satellite.

Astronomers had known the asteroid was coming and said there was no risk of collision. Other asteroids have been known to pass by closer to our planet. And, of course, sometimes the slam into us. Car-sized objects streak into our atmosphere several times a year. Most burn up in the atmosphere or land in the ocean (the planet surface is two-thirds water).

Asteroids as big as the 1908 Tunguska object that devastated the Siberian forest might strike Earth as often as once every two centuries, scientists speculate. As space rocks enter Earth's atmosphere, smaller ones can break apart or explode before hitting the surface. If one were to strike or explode above a city, the results would be locally devastating.

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