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Second asteroid detected before it hit the Earth

Paul Sutherland, Feature writer
Jan 4, 2014, 8:00 UTC

Sen—For only the second time ever, astronomers have detected an asteroid heading our way in space before it actually collided with the Earth’s atmosphere.

The space rock in question was the first to be discovered in the New Year, earning it the label 2014 AA. Estimated to be up to three metres across, or similar in size to a small car, it was spotted on 1 January by Richard Kowalski using a telescope on Mt Lemmon, Arizona, that is part of the Catalina Sky Survey.

The survey’s value as an early warning system for incoming cosmic missiles proved itself, but we had only 25 hours warning because the asteroid impacted our atmosphere early the next day.

A similar-sized asteroid became the first to be found in advance in a similar way a little over five years ago, again by Kowalski using the 1.5-metre telescope on Mount Lemmon. That one, labelled 2008 TC3 exploded above the Sudan showering the Nubian Desert with fragments on 7 October 2008.

The initial images of the latest impactor were recorded by a 1.5-metre (60in) telescope on Mount Lemmon. Their short track allowed astronomers to calculate only a rough orbit for the asteroid but showed that it was only 500,000km away when discovered. Calculations suggested it would probably enter the atmosphere at about 02.33 UT, plus or minus 1h 5m.

Faint signals from the blast when it hit the atmosphere were recorded by three infrasound stations that listen out for nuclear explosions for the Comprehensive Nuclear-Test-Ban Treaty Organization.

They showed that the asteroid hit us between Central America and East Africa and that any fragments landed in the sea. Its entry is sure to have produced a brilliant fireball and astronomers are keen to find out if anything was spotted from ships in the Atlantic.

Discovery images of asteroid 2014 AA revealed its swift motion across the sky. Credit: Catalina Sky Survey, Lunar & Planetary Laboratory, University of Arizona

The earlier incoming asteroid to be spotted in advance was estimated to weigh 80 tonnes and it broke up and rained hundreds of fragments across the Nubian Desert.

NASA meteor expert Peter Jenniskens led an expedition of Sudanese students who retrieved nearly 280 meteorites, 4.5 billion year-old relics from the early Solar System that will help tell scientists how the planets formed.

Last year, the biggest cosmic missile to hit the Earth for a century arrived without any warning whatsoever and exploded over the Siberian city of Chelyabinsk. Dubbed a superbolide, the asteroid lit up the Russian sky like a second Sun shortly after sunrise and was captured by many cameras, including the dashcams that are fitted to many Russian cars.

That meteor, which was probably about 18-metres across when it entered the atmosphere, weighing 11,000 metric tons, exploded with more than 30 times the energy of the atom bomb that devastated Hiroshima.

It produced an airblast that shattered windows, damaged buildings and injured more than 1,000 people before showering meteorites around Lake Chebarkul. A giant piece was discovered by divers in the lake itself.

By the end of last year, NASA said that sky surveys had detected 10,000 asteroids that pose a collision threat with the Earth. Those Near Earth Asteroids or Potentially Hazardous Objects found range in size from large boulders a few tens of centimetres across to the largest, 1036 Ganymed, which is 41 km (25 miles) wide. About ten per cent of them are greater than 1km in size, and so would cause significant destruction if they impacted.

The vast majority of NEOs are smaller than 1km and there are thought to be around 15,000 with diameters of about 140 metres. However, millions of much smaller asteroids are still lurking undiscovered out there.