Study warns of 'gravitational keyholes' which could push doomsday space rock onto a path which means it will hit us one day (Image: Getty)
Study warns of ‘gravitational keyholes’ which could push doomsday space rock onto a path which means it will hit us one day (Image: Getty)

In less than ten year’s time, a huge icy space rock taller than the Eiffel Tower will travel perilously close to Earth.

Named after the Egyptian god of chaos, Asteroid 99942 Apophis is big enough to kill tens of millions of people if it were to hit our planet.

It will be visible from Earth as it zooms past us on Friday, April 13, 2029, and comes close enough to ‘graze’ the region in which satellites travel around the world.

You might think humanity will be able to breathe a sigh of relief when Apophis speeds away from us and resumes its lonely journey through the void.

Yet there’s a chance it will encounter one of Earth’s ‘gravitational keyholes’ during this flyby, pulling it onto a course which would result in a ‘devastating impact’ in 2036.

Now a Nasa-backed study from the Massachusetts Institute of Technology (MIT) has exposed the risk posed by our planet’s keyholes – but also presented a new way of protecting ourselves from Apophis or any other doomsday space rock that comes our way.

‘People have mostly considered strategies of last-minute deflection when the asteroid has already passed through a keyhole and is heading toward a collision with Earth,’ said Sung Wook Paek, lead author of the study and a former graduate student in MIT’s Department of Aeronautics and Astronautics.

‘I’m interested in preventing keyhole passage well before Earth impact. It’s like a preemptive strike, with less mess.’

There are two ways of stopping an asteroid from hitting us. The first involves hitting it with a nuclear bomb, but this risks showering Earth with radioactive fallout.

The other involves smashing a ‘kinetic impactor’ spacecraft into it and therefore changing the object’s trajectory so it doesn’t hit us.

Paek considered this second option and used simulations to work a way of steering objects onto a new course and ‘closing the keyhole’ so it doesn’t become snared on a path which means it will hit Earth.

‘A keyhole is like a door – once it’s open, the asteroid will impact Earth soon after, with high probability,’ Paek added

The researchers tested their simulation on Apophis and the famous ‘apocalypse asteroid’ Bennu, which are ‘two of only a handful of asteroids for which the locations of their gravitational keyholes with respect to Earth are known’.

A graphic demonstrating the size of Apophis (Image: Wikimedia Commons)
A graphic demonstrating the size of Apophis (Image: Wikimedia Commons)
This is the 'apocalypse asteroid' Bennu. It has a very, very small chance of hitting us next century (Image: Nasa)
This is the ‘apocalypse asteroid’ Bennu. It has a very, very small chance of hitting us next century (Image: Nasa)

They simulated various distances between each asteroid and their keyholes, calculating a ‘safe harbour’ region into which an asteroid would have to be deflected so that it would avoid both an impact with Earth and dodge other gravitational keyholes.

The team also said it was very important to understand the make-up of apocalypse asteroids so that we can work out how best to deflect it.

They found that if Apophis passes through a keyhole in five years or more, there is enough time to send a craft to measure the asteroid’s dimensions and another ‘to nudge it slightly off track as a test’ before sending a main ‘impactor’ to smash into it so it’s steered away from Earth.

If it passes through a keyhole within two to five years, we’ll only have time to send one spaceship up to measure it dimensions before launching the impactor

But if Apophis crashes through its keyhole within one Earth year or less, it may be too late to save ourselves from disaster.

‘Even a main impactor may not be able to reach the asteroid within this timeframe,’ Paek warned.

‘Instead of changing the size of a projectile, we may be able to change the number of launches and send up multiple smaller spacecraft to collide with an asteroid, one by one. Or we could launch projectiles from the moon or use defunct satellites as kinetic impactors.

‘We’ve created a decision map which can help in prototyping a mission’