'Doomsday asteroid’ that could crash into Earth passes close by

Thursday, January 10, 2013
ESA's telescope captures image of the massive asteroid Apophis as it passes close to Earth, revealing it to be
much bigger than it was expected. It has been described as a 'doomsday asteroid'  because Scientists predicted
that it could hit our planet in April, 2029  [Image Credit: NASA/ESA/Herschel/PACS/MACH-11/MPE/ESAC]
Washington: Scientists using European Space Agency's Herschel Space Observatory made new observations of asteroid Apophis as it approached Earth this past weekend. The data show the asteroid to be bigger than first estimated, and less reflective.

Discovered in 2004, Apophis has been described as a 'doomsday asteroid' because of a study that predicted a 2.7% chance of the rock hitting Earth when it passes within 22,364 miles of our planet in April 2029.

Additional observations of the asteroid ruled out any possibility of an impact in 2029.

However, Apophis is expected to make a record-setting -- but harmless -- close approach to Earth on April 13, 2029, when it comes no closer than 18,300 miles (29,450 kilometers) above Earth's surface.

The asteroid will make another approach to Earth in 2036. Data collected by telescopes during today's close approach are expected to refine the asteroid's orbit to the point where an impact in 2036 can be ruled out.

Over the weekend, Herschel gathered data while observing Apophis for about two hours on its approach to Earth, ahead of today's closest encounter at a little less than one-tenth of the distance from Earth to the sun: about 9 million miles (14.5 million kilometers).

The space observatory provided the first thermal infrared observations of Apophis at different wavelengths, which together with optical measurements helped refine estimates of the asteroid's properties.

Previous estimates bracketed the asteroid's average diameter at about 885 feet (270 meters). Herschel's observations indicate the space rock is about 10,060 feet (325 meters) across.

By analyzing the heat emitted by Apophis, Herschel also provided a new estimate of the asteroid's albedo -- a measure of its reflectivity-- of 0.23. This value means that 23 percent of the sunlight falling onto the asteroid is reflected; the rest is absorbed and heats up the asteroid. The previous albedo estimate for Apophis was 0.33.

The Herschel Observatory is a European Space Agency mission in which NASA plays an important role.
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