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Asteroid flies by Earth closer than any seen before, Nasa says

Andrew Griffin
Wednesday 19 August 2020 07:22 BST
Emails reveal that an asteroid 100 metres wide 'slipped through' Nasa's detection systems
Emails reveal that an asteroid 100 metres wide 'slipped through' Nasa's detection systems (Getty Images/iStockphoto)

An asteroid has flown past Earth closer than any seen before.

The tiny object, known as asteroid 2020 QG, came just 1,830 miles over the southern Indian Ocean on Sunday, the space agency said.

As it did so, it was spotted by the Zwicky Transient Facility, a robotic camera that scans the sky in search of a variety of objects, from the smallest asteroids to the largest supernova.

The asteroid 2020 QG is particularly small. It is about three to six meters across, scientists said, roughly the size of a large car.

Its small size meant that it never posed much of a threat to Earth. If it had flown towards us rather than just past, it would have turned into a fireball and broken up in Earth's atmosphere, as numerous small asteroids do each year.

By flying by so closely, however, it has entered the record books as the closest asteroid known to have flown past Earth.

“It’s really cool to see a small asteroid come by this close, because we can see the Earth’s gravity dramatically bend its trajectory,” said Paul Chodas, director of the Center for Near-Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory.

“Our calculations show that this asteroid got turned by 45 degrees or so as it swung by our planet.”

Such asteroids are not thought to be rare – an object of this size passes by this close to Earth once a year or so. But it is spotting it as it does that is difficult, with new technology allowing such small objects to be spotted more easily.

Nasa needs to be able to track these near-Earth asteroids in case any of them are large and close enough to put Earth in danger. The space agency has been tasked with finding 90 per cent of near-Earth asteroids that are 140 meters or bigger, since those objects could pose a significant threat and are easier to spot from a distance.

“It’s quite an accomplishment to find these tiny close-in asteroids in the first place, because they pass by so fast,” Chodas said. “There’s typically only a short window of a couple of days before or after close approach when this small of an asteroid is close enough to Earth to be bright enough but not so close that it moves too fast in the sky to be detected by a telescope.”

The object was discovered by looking through the images from the ZTF, as part of a Nasa-funded programme to track and study such asteroids. As they fly across the sky, they leave streaks across the ZTF images, and every night an algorithm looks through about 100,000 pictures in search of those streaks, forwarding any promising ones onto staff for further investigation.

“A lot of the streaks are satellites, but we can quickly go through the best images by eye to find the actual asteroids,” said Bryce Bolin, a postdoctoral scholar in astronomy at Caltech and a member of the ZTF team. “This latest find really demonstrates that ZTF can be used to locate objects very close to Earth that are on potentially impacting trajectories.”

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