Giant space rock slicing past Earth

– A house-size asteroid will give Earth a near-miss tomorrow, passing harmlessly inside the Moon’s orbit while giving experts a rare chance to rehearse for a real-life strike threat.

Dubbed 2012 TC4, the space rock will shave past at an altitude of less than 44 000km – just above the 36 000km plane at which hundreds of geosynchronous satellites orbit the Earth. That represents about an eighth of the distance between the Earth and the Moon.

Nasa’s Mike Kelley, who is leading the exercise to spot, track and probe the visitor, insisted there was “no danger. Not even for satellites”.

“We’ve now been observing TC4 for two months so we have very accurate position information on it, which in turn allows very precise calculations of its orbit,” which will not cross that of Earth nor its satellites.

The object was first spotted five years ago when it called on Earth at about double tomorrow’s projected distance, before disappearing. It is 15 metres to 30 metres wide – about the size of the meteoroid that exploded in the atmosphere over Chelyabinsk in Russia in 2013, with 30 times the kinetic energy of the atomic bomb dropped on Hiroshima. The resulting shockwave blew out the windows of nearly 5 000 buildings and injured more than 1 200 people.

While the Chelyabinsk event caught everyone unaware, TC4 is one of thousands of space rocks the whereabouts of which are known. Millions are not.

On its 609-day loop around the Sun, TC4 will return to Earth in 2050 and 2079, according to Ruediger Jehn of the European Space Agency’s (ESA) Near-Earth Object programme in the Netherlands. “We know it will also not hit the Earth in the year 2050, but the close flyby in 2050 might deflect the asteroid such that it could hit the Earth in 2079,” he said.

Flybys like this one are quite common – about three objects similar in size to TC4 graze past at a similar distance every year. What makes TC4 special is that it has been chosen to test the global asteroid pre-warning system, fed by a network of observatories, universities and labs around the world.

The asteroid’s close approach will allow teams to evaluate how accurate they were in predicting its orbit and size, while using telescopes to learn more about its composition. Jehn’s colleague, Detlef Koschny, said: “We are practising for the real serious case.”

Many scientists believe the Earth will again be hit by a space rock of the size that wiped out the dinosaurs, though nobody knows when. TC4 will make its closest approach to Earth just before 05.41 GMT tomorrow, at a point south of Australia, ESA and Nasa said. It will not be visible to the naked eye nor with binoculars, “but it can be seen in the night of October 11-12 from European observatories”, Jehn said. –

Paris