European Space Agency spacecraft to steer asteroids away from Earth
Hollywood films would have you believe that the best way to deal with an Earth-threatening asteroid is to blast it out of orbit.
But the European Space Agency (ESA) is looking at a far subtler approach to saving the planet – a gravity tractor.
The plan involves sending a spacecraft to rendezvous with a dangerous asteroid and use its tiny gravitational field to slightly alter the space rock's trajectory so that, over time, it would soar harmlessly past Earth.
It is an idea that has been floated for decades, but recently become more pressing after the 2024 YR4 scare earlier this year, an asteroid that came seemingly out of nowhere and at one point had a one in 32 chance of hitting Earth in December 2032.
Joseph Aschbacher, director general of ESA, admitted he had been ''very worried' about 2024 YR4 and said the space agency was stepping up its planetary defence capabilities.
Speaking to The Telegraph at Space-Comm expo this week, Dr Aschbacher said: 'I was very worried.
'If the asteroid is in front of your door, more or less, it's too late, and we probably cannot do much.
'The earlier you detect an asteroid that might impact planet Earth, and the earlier you can take action far away from planet Earth, the higher the chances are that it will not have negative impacts.
'(A planetary defence mission) may actually start, by just sending a satellite there, and letting it fly close by the asteroid so that the gravity of the satellite influences the gravity of the asteroid itself.
'Slightly by degrees, it would change the trajectory, and therefore may result in a different trajectory than the ones that might be directed to Earth. So the further away you can do it, the bigger the chances of minimising damage.'
Apophis rock no longer a risk
Last year, ESA announced that it planned to rendezvous with the asteroid 99942 Apophis, a cruise ship-sized rock, which makes an exceptionally close flyby of Earth in April 2029, when it will be visible to the naked eye.
The mission, called Ramses (Rapid Apophis Mission for Space Safety), will give a crucial window into how asteroids are affected by gravitational forces – in this case, the gravity of Earth.
Apophis was predicted to get dangerously close to Earth in 2068, but experts have since revised their calculations and no longer see it as a risk.
'We have a mission planned already to encounter that asteroid before it comes to Earth, and to really measure it,' added Dr Aschbacher.
'We are not assuming it will hit planet Earth, but it will fly by very closely, and that will be quite a spectacle, in terms of every citizen being able to see it, but it is a unique opportunity to really study the asteroid close by.'
Most asteroids and comets have orbits that do not bring them very close to Earth, and they are only classed as dangerous if they come within 4.6 million miles and are larger than 460 feet.
But occasionally they can hit. The last major impacts include the Tunguska event in 1908 in Siberia which felled an estimated 80 million trees, while the 2013 Chelyabinsk meteor is the only known incident in modern times which resulted in numerous injuries.
Only one asteroid deflection test has ever taken place in space. In 2022, Nasa sent its Dart (Double Asteroid Redirection Test) spacecraft to crash into Dimorphos, a 525ft-wide 'moonlet' which circles a larger asteroid called Didymos.
The team had hoped the impact would shorten Didymos' 11 hour 11 minute orbit by a few minutes, but it ended up shaving off around half an hour.
However, the impact had unexpected consequences, unleashing a storm of boulders 'as deadly as Hiroshima' and proving that deflection strategies could have unintended consequences that leave smaller rocks on a collision course with Earth.
In contrast, a gravity tractor would cause less collateral damage, gently nudging an Earth-bound asteroid in a new trajectory.
Last year, ESA launched a spacecraft, named Hera, which is travelling to Didymos-Dimorphos to assess the true scale of the damage in a mission which will help determine which asteroid defence scheme will be chosen in the event of another scare. It is due to arrive in October next year.
Dr Paul Bate, the chief executive of the UK Space Agency, said: 'Asteroids are one of the ways in which you show the power in space, so we are right to be worried.
'Whether we like it or not, these things have been happening literally since the start of the solar system. We're connected.
'We don't have any choice, but we know we can actively choose to understand more and that's very important for deflection, for protecting our planet.'
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