An asteroid as big as a 10-story building has passed by Earth at a distance half that of the Moon, researchers have revealed.

The asteroid, dubbed 2017 AG13, was only spotted only Saturday by the University of Arizona's Catalina Sky Survey.

It is between 50 and 111 feet (15 to 34 meters) long, and when it passed by Earth, 2017 AG3 was moving at 9.9 miles per second (16 kilometers per second).

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2017 AG13, was discovered Saturday by the University of Arizona's Catalina Sky Survey.Between 50 and 111 feet long, when it passed it was moving at 9.9 miles per second. Here, it is so close to Earth its text is almost unreadable.

WHAT WOULD HAVE HAPPENED IF IT HIT? According to an asteroid-impact simulator called 'Impact Earth!' by Purdue University, if a porous rock asteroid of 111 feet (34 meters) long hit Earth at a 45-degree angle, the simulator found, it would have exploded as an air burst. The site says the blast would have released about 700 kilotons' worth of energy — dozens of times more powerful than the atomic bomb detonated over Hiroshima. However, since it would have occurred from a distance of about 10 miles high, it probably wouldn't have had much effect on the ground; if anything, a high-altitude boom may have sounded as loud as heavy traffic on the ground. Advertisement

The near-Earth object, or NEO, came within about half the distance that the moon is from Earth, according to Slooh.

'This is moving very quickly, very nearby to us,' Eric Feldman, an astronomer with Slooh, said during a live broadcast of the flyby at 7:47 a.m. ET on January 9.

'This one has a particularly elliptical orbit.

'It actually crosses the orbits of two planets, Venus and Earth.

Slooh's broadcast said 2017 AG3 was 'roughly the same size as the asteroid that struck Chelyabinsk, Russia in 2013,' meaning had it hit, the effects would have been similar.

Its next close approach to Earth is expected on December 28, 2017.

'It is not that uncommon of an event, which is one of the reasons it is interesting,' Mark Sykes, director and CEO of the Planetary Science Institute, told Business Insider in an email.

About 38 more 'close approaches' like asteroid 2017 AG3's are expected within the month of January alone, according to NASA's Near Earth Object Program.

For years scientists have been trying to work out how to deal with the threat of an asteroid, which could hit us with little or no warning.

Now the White House has released an official document describing the plan if a meteor or asteroid was to head our way, and it shows we are under-prepared.

'This is moving very quickly, very nearby to us,' Eric Feldman, an astronomer with Slooh, said during a live broadcast of the flyby at 7:47 a.m. ET on January 9.

The White House published its 'National Near-Earth Object Preparedness Strategy'.

The document 'seeks to improve our nation's preparedness to address the hazard of near-Earth object (NEO) impacts by enhancing the integration of existing national and international assets and adding important capabilities that are currently lacking.'

NEOs are asteroids or comets that have an orbit that brings them near or into Earth's orbit.

Slooh's broadcast said 2017 AG3 was 'roughly the same size as the asteroid that struck Chelyabinsk, Russia in 2013,' meaning had it hit, the effects would have been similar.

If one of these was to zoom towards Earth in the future, it would not be the first time.

A 56 foot (17-metre) meteor that struck Chelyabinsk, Russia, in 2013, injured more than 1,000 people came with no warning.

This is why one of the strategies outlined in the document is to improve on Nasa's methods of detecting NEOs before it is too late.

The White House has released an official document describing the plan if a meteor or asteroid was to head our way, and it shows we are under-prepared. Artist's impression pictured

THE SEVEN MAIN GOALS Enhance NEO detection, tracking and characterization capabilities. Develop methods for NEO deflection and disruption. Improve modelling, predictions, and information integration. Develop emergency procedures for NEO impact scenarios. Establish NEO impact response and recovery procedures. Leverage and support international cooperation. Establish coordination and communications protocols and thresholds for taking action. Advertisement

In seven main goals described in the document, the White House also focuses on improving modelling and predicting where NEOs will travel.

The country also plans to improve it emergency alert systems and invest in hi-tech space probes that could annihilate threats.

The document notes, as with other low-probability, high-consequence hazards, 'potential NEO impacts pose a significant and complex challenge.'

'This Strategy is a step in addressing the myriad challenges of managing and reducing the risks posed by both large and small NEOs,' it claims.

At the end of last year, Nasa warned we are not prepared for an asteroid strike.

Dr Joseph Nuth, a researcher at Nasa's Goddard Space Flight Centre in Maryland was speaking at the annual meeting of the American Geophysical Union in December.

He said: 'The biggest problem, basically, is there's not a hell of a lot we can do about it at the moment.'

In the 1998 film Deep Impact, a comet is hurtling toward Earth and could mean the end of all human life. The US government keeps the crisis under wraps, but a crack reporter uncovers the truth, forcing U.S. President Beck (Morgan Freeman, pictured) to announce his plan

NASA'S ASTEROID REDIRECT MISSION Nasa is planning an ambitious mission that will see a robotic spaceship visit an asteroid to create an orbiting base for astronauts. The robot shipwill pluck a large boulder off the space rock and sling it aroundthe moon, becoming a destination to prepare for futurehuman missions to Mars. Nasa plans to study the asteroid for about a year and test deflection techniques that one day may be necessary to save Earth from a potentially catastrophic collision. Advertisement

While dangerous asteroids and comets rarely hit Earth, Dr Nuth warned that the threat was always there.

He said: 'They are the extinction-level events, things like dinosaur killers, they're 50 to 60 million years apart, essentially.

'You could say, of course, we're due, but it's a random course at that point.'

Nasa is working on a series of missions including an asteroid redirect mission, that will see a robotic spaceship visit an asteroid to create an orbiting base for astronauts.

The space agency has a team of scientists who are always watching the skies for potential threats.

But while the US is upping its tactics to seek out the dangerous space rocks, other countries might be even less prepared.

In a planned mission, a robot ship will pluck a large boulder off an asteroid and sling it around the moon, becoming a destination to prepare for future human missions to Mars, the US space agency revealed last year

In the Spacecraft Structures Lab at Nasa's Langley Research Center, the Asteroid Redirect Mission robotic contact and restraint system was prototyped and tested

The US is undecided on whether to invest and prepare costly space technology to intercept those that will not affect its own country.

The document, however, suggests the country is looking to collaborate with other nations in the future.

'NEO impacts are a global hazard and could have major environmental, economic, and geopolitical consequences detrimental to the United States, even if the impact is beyond US territory,' it says.

'Although currently a global leader in detecting and tracking NEOs, the United States will depend (in part) on international cooperation and coordination to help develop capabilities for characterization and future capabilities related to the development and implementation of deflection and disruption capabilities for NEOs.'

