The European Space Agency's Herschel space telescope took the photographs of the asteroid Apophis, dubbed the "doomsday asteroid" by the media when initial observations in 2004 yielded a 2.7 percent chance of it striking the Earth in 2029.
Subsequent analysis has ruled out a collision, though the asteroid will pass within 22,000 miles of Earth, closer than the orbits of many satellites, a release from the ESA's Paris headquarters said Wednesday.
Herschel observed the asteroid for about 2 hours on its approach to Earth, which it will pass at a distance of about 8 million miles late Wednesday.
"As well as the data being scientifically important in their own right, understanding key properties of asteroids will provide vital details for missions that might eventually visit potentially hazardous objects," Laurence O'Rourke of the the European Space Astronomy Center near Madrid, said.
Previous calculations had put the asteroid's average diameter at 880 feet, but the Herschel observations returned a more precise diameter of 1,066 feet.
"The 20 percent increase in diameter, from 270 to 325 meters [880 to 1,066 feet] translates into a 75 percent increase in our estimates of the asteroid's volume or mass," said Thomas Muller of the Max Planck Institute for Extraterrestrial Physics in Germany, who is leading the analysis of the new data.
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