Author: The Conversation / Source: The Next Web
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.
So where did this asteroid come from?
At risk from space debris
The Solar system is littered with material left over from the formation of the planets. Most of it is locked up in stable reservoirs – the Asteroid belt, the Edgeworth-Kuiper belt and the Oort cloud – far from Earth.
Those reservoirs continually leak objects into interplanetary space, injecting fresh debris into orbits that cross those of the planets. The inner Solar system is awash with debris, ranging from tiny flecks of dust to comets and asteroids many kilometers in diameter.
The vast majority of the debris that collides with Earth is utterly harmless, but our planet still bears the scars of collisions with much larger bodies.
The largest, most devastating impacts (like that which helped to kill the dinosaurs 65 million years ago) are the rarest. But smaller, more frequent collisions also pose a marked risk.
In 1908, in Tunguska, Siberia, a vast explosion leveled more than 2,000 square kilometers of forest. Due to the remote location, no deaths were recorded. Had the impact happened just two hours later, the city of St Petersburg could have been destroyed.
In 2013, it was a 10,000-tonne asteroid that detonated above the Russian city of Chelyabinsk. More than 1,500 people were injured and around 7,000 buildings were damaged, but amazingly nobody was killed.
We’re still trying to work out how often events like this happen. Our information on the frequency of the larger…
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