How to protect Earth from asteroid strikes

The recent film ‘Don’t Look Up’ follows the story of two astronomers who have spotted a ‘planet killing’ comet on a direct collision course with Earth and their subsequent struggles to convice world powers to act to deflect the incoming object. But what is the process in reality?

If an object in space comes within 1.3 astronomical units (one unit is the average distance between the Earth and Sun), then it is classified as a near Earth object (NEO). Anything above 140 metres in diameter is considered a potential hazard to Earth. 

"Telescopes are constantly comparing images of the sky to see if anything is 'moving'", says Huw James, fellow of the Royal Astronomical Society. 

If it appears that an object is 'on the move', the co-ordinates, velocities and orbit are sent to the Minor Planet Centre database to check whether the newly-spotted object is already known or whether it is in fact a new discovery.

Around 3,000 new near Earth asteroids are found every year. This may seem like an alarming number, but James reassures that, "we’re finding more per year because technology is getting better; it doesn’t mean there are more hazards out there."

Small objects regularly burn up on entry to our atmosphere and can be seen as shooting stars. NASA predict that anything less that a kilometre in size would havedevastating but local effects on Earth. "Anything larger than that could have worldwide effects," says James. "To give perspective, the object that struck Earth causing the extinction of dinosaurs is estimated to be 10 km in diameter."

So how can we protect Earth from potentially devastating impact strikes?

The recent DART mission (double asteroid redirection test), launched in November 2021, is exploring whether it is possible to deflect the path of an asteroid away from Earth through impact. "The good news is that at the massive distances involved, you only really need a small bump to send [the asteroid] way off the path of Earth," says James. However, the closer the object is to Earth on discovery, the harder it may be to deflect the path sufficiently.

Other innovative methods are being designed to change the trajectory of an incoming object, such as: 

• Gravity tractors - a thereoretical spacecraft that hovers near an aseroid, deflecting the trajectory through its own gravitational pull.
• Asteroid laser ablation - using a laser to vapourise the surface of an asteroid, creating an ejection of material and subsequent thrust, working to alter the asteroid's trajectory.
• Solar sails - using a sail to block sunlight from reaching the object, reducing the heating effect of the Sun. The result of heating one side of an object causes an effective thrust, that once removed through the use of a solar sail could alter the trajectory of the object. 

Although these methods still remain theoretical, we are working to build our armoury of tools that can be used to protect Earth. In the meantime, DART is due to 'strike' in September 2022, so we shall see how effective our cosmological bat will be later this year...