Earth will say hello to a cosmic visitor Sunday, as a giant asteroid scientists have dubbed "The Beast" is expected to fly past our planet rather closer than is comfortable.

The asteroid, only spotted on April 23 by NASA's Wide-field Infrared Survey Explorer, is more than a thousand feet across.

It was first thought to be even bigger because of its observed brightness, but further measurements as it approached Earth yielded the current estimates of its size.

Thee Minor Planet Center of the International Astronomical Union has classified the space rock, officially named 2014 HQ124, as a "Potentially Hazardous Asteroid."

The asteroid will pass the Earth at a distance of around 700,000 miles, or three times the distance at which the Moon orbits us.

That's close enough for concern, some astronomers say.

"What's disconcerting is that a rocky/metallic body this large, and coming so very close, should have only first been discovered this soon before its nearest approach," says Bob Berman, an astronomer with the Slooh Space Camera organization.

"HQ124 is at least 10 times bigger, and possibly 20 times [bigger], than the asteroid that injured a thousand people last year in Chelyabinsk, Siberia," Berman says. "If it were [to] impact us, the energy released would be measured not in kilotons like the atomic bombs that ended World War II, but in H-bomb type megatons."

At its closest approach to Earth at around 2 a.m. EDT, the asteroid will be travelling at speeds of around 31,000 miles per hour.

NASA has recently joined with the Slooh organization in an effort to attract citizen scientists to help search for and identify near-Earth objects like HQ124.

As part of the space agency's Asteroid Grand Challenge, they will be encouraged to use Slooh telescope data to dsicover and monitor objects the size of HQ124 and smaller.

While previous and current sky surveys have been called successful in identifying 90 percent of asteroids 3,200 feet in diameter and larger, many smaller bodies that could still represent a risk to our planet have not yet been found or tracked, NASA says.

Less than a third of objects about 460 feet across and just 1 percent of those 100 feet in diameter have been detected, the space agency estimates.

NASA scientists have put the number of near-Earth objects with a diameter of around 100 feet at a million, most of them still to be identified.

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