On Sunday, June 10, a potentially hazardous asteroid thought to have been 500 meters (0.31 miles) wide was discovered by Siding Spring Observatory in New South Wales, Australia. Fortunately for us, asteroid 2012 LZ1 drifted safely by, coming within 14 lunar distances from Earth on Thursday, June 14. Phew.

But as it turns out, this particular space rock was a civilization-killing asteroid in disguise.

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Last week, asteroid 2012 LZ1′s discovery stirred some excitement, prompting NASA’s Asteroid Watch to tweet a response:

A bit stumped over the hype surrounding asteroid 2012 LZ1 today. Huge? No; Close? Not really (3.4 million miles); A danger? No. — Asteroid Watch (@AsteroidWatch)

This particular asteroid may not have been a danger, but much of the concern was rooted in the late warning of its detection — 2012 LZ1 was spotted only four days before closest approach.


One of the reasons for its late discovery is because it was detected in Southern Hemisphere skies, part of the world were we have few asteroid-watching programs. If it had been on a collision course with Earth, a few days notice is no time at all.

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So, in the aftermath of the flyby, astronomers at the famous Arecibo Observatory in Puerto Rico used radar to image the interplanetary interloper (pictured top). What they uncovered was a surprise: Asteroid 2012 LZ1 is actually bigger than thought… in fact, it is quite a lot bigger. 2012 LZ1 is one kilometer wide (0.62 miles), double the initial estimate.

Why such a discrepancy in size estimates?

The Arecibo team has determined that 2012 LZ1′s surface is really dark, reflecting only 2-4 percent of the light that hits it — this contributed to the underestimated initial optical observations. Looking for an asteroid the shade of charcoal isn’t easy.

Arecibo uses a powerful radar system — called the Arecibo Planetary Radar — to generate radio waves that were beamed in the asteroid’s direction. Incredible high-resolution images of surface features were attained by measuring the signals that bounced back to the radio antennae. Highly accurate measurements of the asteroid’s physical size could be made.

“This object turned out to be quite a bit bigger than we expected, which shows how important radar observations can be, because we’re still learning a lot about the population of asteroids,” said Arecibo Observatory’s Ellen Howell in a statement.

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The followup observations have also helped astronomers make precision measurements of the asteroid’s trajectory and other orbital characteristics. With the help of Arecibo, astronomers have deduced that Earth will be safe from being hit by 2012 LZ1 for at least 750 years.

“The sensitivity of our radar has permitted us to measure this asteroid’s properties and determine that it will not impact the Earth at least in the next 750 years,” said Mike Nolan, Director of Planetary Radar Sciences at Arecibo Observatory.

Interestingly, this news coincided with Thursday’s Space Hangout, when Fraser Cain (Universe Today), Alan Boyle (MSNBC/Cosmic Log), Amy Shira Teitel (Discovery News/Vintage Space), Mike Wall (SPACE.com) and myself meandered into talking about the importance of increased asteroid detection funding:

Source and image credit: Arecibo Observatory