When an asteroid exploded over Russia’s Chelyabinsk Oblast in February 2013 with 30-times the force of the Hiroshima nuclear bomb, more than 7,000 buildings were damaged. The asteroid’s arblast blew out windows in a wide radius, injuring more than 1,000 people with razor-sharp shards of glass. US space agency NASA dubbed the asteroid impact a “wake-up call” to the cosmic dangers lurking in the depths space. Then, a similar incident occurred on December 18 last year when NASA’s satellites traced a monstrous asteroid explosion over the Bering Sea, off of the coast of Alaska and Russia.
Thankfully, the blast avoided any residential areas but Jonti Horner, a professor of astrophysics at the University of Southern Queensland, said it is proof of the constant barrage of space rocks striking the Earth.
In an article for The Conversation, Dr Horner said: “Earth is often in the firing line of fragments of asteroids and comets, most of which burn up tens of kilometres 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 10 metres across detonated with an explosive energy ten times greater than the bomb dropped on Hiroshima.”
But why did we not see the asteroid creep up on the Earth until the very last minute? And how often do these strikes occur?
Earth is often in the firing line of fragments of asteroids and comets
Jonti Horner, University of Southern Queensland
According to the asteroid expert, the solar system is absolutely littered with rocky material left over from the forming days of the planets.
Most of thee asteroids are locked in an orbit of the Sun in Asteroid Belt between Mars and Jupiter and the Kuiper Belt on the outskirts of the system.
For the most part, the space rocks are far from the Earth but the asteroid belts “leak” material into the inner circles of the solar system.
When this happens, the cosmic debris often crosses paths with the Earth and occasionally strikes the planet at full speed.
These asteroids range in size from grains of sand to 10,000-tonne rocks like the one over Russia in 2013.
And once in a while, an asteroid big enough to wipe out most life on Earth appears, just like the one which killed the dinosaurs 65 million years ago.
Dr Horner said: “Before we can quantify the threat an object poses, we first need to know that the object is there. But finding asteroids is hard.
“Surveys scour the skies, looking for faint star-like points moving against the background stars.
“A bigger asteroid will reflect more sunlight, and therefore appear brighter in the sky – at a given distance from Earth.
“As a result, the smaller the object, the closer it must be to Earth before we can spot it.”
Objects the size of the infamous Chelyabinsk meteor, about 65.6ft (20m) across, can only be spotted when they pass really close to Earth.
Dr Horner said this means asteroid impacts on this scale are “really the norm” rather than an exception.
He said: “The Chelyabinsk impact is a great example. Moving on its orbit around the Sun, it approached us in the daylight sky – totally hidden in the Sun’s glare.
“For larger objects, which impact much less frequently but would do far more damage, it is fair to expect we would receive some warning.”
According to NASA, there are currently no known large objects on direct collision paths with the Earth.
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