Space detectives have ended a celestial “manhunt” by tracking down one of the biggest cosmic missiles to threaten the Earth.

Astronomers rediscovered a giant space rock more than 500 ft (150 metres) wide that was lost way back in 1960. It is officially termed a “potentially hazardous object” because it comes close enough to collide.

The scientists worked out that a newly discovered asteroid called 2007 RR9 is actually the same as the long-lost chunk of cosmic debris labelled 6344 P-L.

Astronomer Peter Jenniskens, of the SETI Institute in California, said: “The object was long recognized to be dangerous, but we didn’t know where it was. Now it is no longer just out there.”

Jenniskens believes that the space rock is actually the giant head of an ancient comet that has lost its gassy tail. He believes smaller fragments that broke away from the comet already strike the Earth from mid-October to early November in a minor meteor shower called the Gamma Piscids.

These fragments swiftly burn up in the atmosphere as “shooting stars” but the comet’s head itself poses a real danger. It is one of only 886 objects bigger than 500 ft wide (150 metres) that cross the Earth’s orbit.

2007 RR9 takes 4.7 years to make one circuit of the Sun, swinging in past us after travelling out beyond the orbit of giant planet Jupiter. There is no currently forecast threat of an impact but the Earth has had other close shaves with disaster.

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