Why it’s so hard to detect dangerous asteroids before they hit Earth

Earth is often in the firing line of fragments of asteroids and comets, most of which burn up tens of kilometers above our heads. But occasionally, something larger gets through.

That’s what happened off Russia’s east coast on December 18 last year. A giant explosion occurred above the Bering Sea when an asteroid some ten meters across detonated with an explosive energy ten times greater than the bomb dropped on Hiroshima.

So why didn’t we see this asteroid coming? And why are we only hearing about its explosive arrival now?

Nobody saw it

Had the December explosion occurred near a city – as happened at Chelyabinsk in February 2013 – we would have heard all about it at the time.

But because it happened in a remote part of the world, it went unremarked for more than three months, until details were unveiled at the 50th Lunar and Planetary Science Conference this week, based on NASA’s collection of fireball data.