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'Lost and found' asteroid returns to buzz Earth Tuesday

Scott Sutherland
Meteorologist/Science Writer

Tuesday, May 15, 2018, 9:09 AM - Lost in space for over 7 years, massive asteroid 2010 WC9 has been found again, and is making a return flyby of Earth on Tuesday, as it passes within the orbit of the Moon.

On May 8, 2018, astronomers at the Mt. Lemmon Observatory, working with Catalina Sky Survey, spotted a large asteroid that was set on a course that would have it passing between the Earth and the orbit of the Moon on Tuesday, May 15. 

Comparing this 'new' object's orbit to ones previous found, the astronomers quickly realized that they had actually rediscovered a lost asteroid - 2010 WC9, which they had first spotted over 7 years ago, on November 30, 2010.

Now, 2010 WC9 is tracking to pass us on May 15, at a distance of over 200,000 km, or just over 50 per cent the distance to the Moon.

The orbital track of asteroid 2010 WC9 during its May 15, 2018 flyby of Earth. Credit: NASA/JPL-Caltech/Scott Sutherland

(RELATED: Got your hands on a meteorite? Here's how to know for sure!)

Losing an asteroid

Rewind the clock back to November 30, 2010, and the same observatory was recording its first observations of an asteroid, which had just safely coasted by Earth and the Moon. It stayed over 9 million kilometres away during its flyby - roughly 24 times the distance to the Moon. Based on its brightness, measured from here on Earth, and some assumptions about its surface albedo (how much sunlight it reflects), the astronomers figured that the asteroid was likely around 70 metres wide. If it was made of even darker stuff than they thought, however, this space rock could have been up to 130 metres wide. It was assigned the designation 2010 WC9, based on the date of its discovery, and it was entered into the various databases kept by NASA, the Minor Planet Center, and others. 

One slightly disturbing fact about 2010 WC9's flyby, though, was that it occurred on November 20, 2010, but it wasn't actually spotted until November 30. So, we hadn't even spotted the object before it passed right by us. Then, just 10 days later, it vanished from sight - it just became too faint for astronomers to spot it with their telescopes.

So, for over 7 years after, 2010 WC9 remained 'lost' - an asteroid spotted only very briefly, so that accurately tracking its orbit is more difficult - and it even had an entry on NASA's Sentry Risk table, which keeps track of asteroids that even have a remote chance of impacting with Earth in the next 100 years.

The chances of an impact from 2010 WC9 were, indeed, small, as they are with all of the objects listed there, but if it were to hit Earth at some point, the effects would be devastating.

For comparison, the asteroid that plunged into the atmosphere on February 15, 2013, and exploded over Chelyabinsk, Russia, was estimated at being around 20 metres wide. That unnamed asteroid, which exploded some 30 kilometres above the ground, blasted apart with the force of a 500 kilotonne bomb. With 2010 WC9 at least three times the size of the Chelyabinsk asteroid, and possibly up to six-and-a-half times larger, it would cause a lot more damage than some broken glass and minor injuries.

Chelyabinsk bolide, Feb 15, 2013. Credit: Gifrific

Now, even though this asteroid will be passing by inside the orbit of the Moon, this is still a safe pass, and asteroid 2010 WC9's orbit has been updated now to the point where it was retired from the Sentry Risk table on May 10, 2018 - just two days after it was re-found.

That means that, going out to at least the year 2200, but probably farther, this asteroid poses no risk to Earth, at all.

(RELATED: Want to find a space rock? Meteorite hunter Geoff Notkin tells us how!)

Interested in seeing what 2010 WC9 looks like to us here on Earth? Watch the Slooh Community Observatory coverage from Tuesday night, which featuring Slooh Astronomers Paul Cox and Dr. Paige Godfrey, who were answering questions about this 'lost and found' asteroid.

To learn more about near-Earth asteroids visit Slooh.com.

Editor's Note: A previous version of this article accidentally misstated the name of this asteroid as "2010 WG9", when it is actually 2010 WC9. This has been corrected, and all other facts about the asteroid, its size and trajectory are unchanged. We apologize for any confusion.

Sources: EarthSky | NASA/JPL-Caltech | Minor Planet Center | Slooh

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