A swarm of mirrors flying in formation in space are the best defence against an asteroid hitting Earth, a study has concluded.

Mirrors sent up into space would reflect the sun’s rays to heat up the asteroid and knock it off course to avoid a devastating impact with the Earth. The technique was found to be the best of several options.

Exploding a nuclear device, as seen in the 1998 film Armageddon, was found to be the next best option.

Massimiliano Vasile, of the University of Glasgow, led a team which conducted modelling tests to assess the chances of success of mirrors and other schemes. A squadron of mirrors was shown to have a high chance of success in pushing asteroids of any size off course and to be feasible technologically, he told a conference at the University of Manchester’s Jodrell Bank Observatory. The nuclear option was found to be highly successful in dealing with large asteroids, such as the one believed to have wiped out the dinosaurs 65 million years ago, but there were safety concerns for smaller space rocks and during the launch.

Mirrors in space, or “solar concentrators”, would direct the sun’s rays against a threatening asteroid to heat the surface sufficiently that it turned to gas. They would be aimed against a small area of the rock, no more than 1.5 metres across, to generate temperatures of at least 2,100C (3,812F).

The evaporating gases would shoot into space, creating the thrust needed to divert the asteroid and prevent a deadly impact. The most serious asteroid threat to the planet identified by astronomers is Apophis which is estimated to be at least 150 metres in diameter and to have a one in 45,000 chance of colliding with the Earth.

In 2029 Apophis’s orbit will take it close enough to Earth for the planet’s gravity to possibly alter its trajectory and dramatically increase the chances of an impact on April 13, 2036. The explosion caused by the impact of Apophis, a medium-sixed asteroid, would be big enough to destroy a city the size of London.

Dr Vasile said: “Asteroid impacts are a real threat. In the past 30 years there have been quite a number of technologies suggested to deflect asteroids. We’ve tried to analyse them to see which are the most effective.”

A large asteroid with a diameter of 1,000 metres would have the potential to cause mass extinctions, and the 10km meteor reputed to have ended the reign of the dinosaurs and created the Chicxulub crater.

An asteroid big enough to cause the extinction of the dinosaurs hits Earth on average every 26 million years, said Dr Vasile. It would take 5,000 mirrors operating for three years to deflect.

The idea of warding off asteroids with mirrors in space was first proposed in 1993 when a single vast reflective surface was suggested. Dr Vasile said a single mirror would be impractical but a series of smaller mirrors acting in concert would be feasible. He was confident it could be developed within a decade.

Nuclear devices would be effective for large asteroids but could leave dangerous fragments falling towards Earth. Equally the danger of an explosion during take-off was unacceptable.

The conference at Jodrell Bank was held to celebrate the 50th anniversary of the Space Age with the launch of Sputnik 1 by the Soviet Union.

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