A Huge Asteroid Exploded Above Earth, and You Totally Missed It

By Ryan F. Mandelbaum on at

The second-largest asteroid to hit Earth in the last 30 years went undetected, until now.

The BBC reports:

At about noon local time on 18 December, the asteroid barrelled through the atmosphere at a speed of 32km/s (20 miles per second) , on a steep trajectory of seven degrees.

Measuring several meters in size, the space rock exploded 25.6km (16 miles) above the Earth’s surface, with an impact energy of 173 kilotonnes.

“That was 40% the energy release of Chelyabinsk, but it was over the Bering Sea so it didn’t have the same type of effect or show up in the news,” said Kelly Fast, near-Earth objects observations program manager at NASA.

The US Air Force first reported that it had detected a fireball on its satellites last year, according to the BBC report. NASA scientist Kelly Fast delivered the news at the 50th Lunar and Planetary Science Conference in the US state of Texas this week.

By 2020, NASA aims to be tracking 90 per cent of near-Earth objects larger than 140 metres ( 460 feet) in diameter, but it’s the smaller rocks that we should be worrying about. Not only are they more frequent, but they can occur without warning, as happened with the 18th December and Chelyabinsk events. Smaller rocks might not threaten the entire globe, but they can cause damage and injuries if they strike populated areas.

There’s lots more work to do on this front, and several possible solutions. The Near-Earth Object Camera, or NEOCam, is a proposed space-based mission to survey smaller objects, but it hasn’t been selected by NASA for launch. In the meantime, if telescopes did spot an asteroid that threatens Earth, astronomers have been practising what their protocol would be.

It’s dangerous business, living on a planet in a Solar System full of rocks and debris.

Featured image: Alex Alishevskikh (Flickr)