A new study suggests we’re safe from big impacts, but it’s the small ones we have to worry about
by COLIN STUART(@skyponderer) Colin is an award-winning astronomy writer and speaker.
ANALYSIS
It’s the ultimate cosmic catastrophe. A killer space rock is locked on a collision course with Earth. When it hits, the curtain comes down on humanity as we fade into the shadows of history, just like the dinosaurs before us. Despite being the subject of a string of apocalyptic Hollywood blockbusters, there is some good news. A recent study found that we’re unlikely to be hit by any of the nearly 1,000 known near-Earth asteroids above a kilometre in diameter within the next millennium (the asteroid that unleashed hell upon Tyrannosaurus rex and co 66 million years ago is thought to have been between 10-15km – 6-9 miles – wide).
The study, led by Oscar Fuentes-Muñoz from the University of Colorado Boulder, is a marked improvement on previous work, which could only forecast a century ahead.
Although, according to Prof Phil Bland, an asteroid expert at Curtin University in Australia, the ‘1,000 impact-free years’ claim comes with some important caveats. Most notably, it only applies to the big asteroids we already know about.
“It doesn’t speak to the five per cent that are still out there waiting to be discovered,” he says. “It doesn’t include comets either, which we’ll never be able to constrain.”
This could be important, as many comets, which can be as big as asteroids, fly in from the outer Solar System having never entered the inner Solar System before. We have no way of tracking them until they’re already very close to us.
Then there are all the asteroids smaller than a kilometre (just over half a mile) across. “We’re not good at all at tracking smaller stuff,” Bland says.
After all, the sky is an incredibly big place and these objects are relatively small. It’s like looking for a tiny, dim needle in an unimaginably large, even darker haystack. For example, some asteroids reflect just five per cent of the sunlight that hits them.
To underscore the potential for a surprise impact, consider the 70m-wide asteroid 2023 DZ2 that passed between Earth and the Moon back in March. Astronomers only spotted it a month beforehand.
Had it hit Earth, it could have levelled a city. This close call came just two months after a truck-sized asteroid dubbed 2023 BU came within 3,600km (2,230 miles) of the
