It is 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 one thousand known near-Earth asteroids above a kilometre in diameter within the next 1,000 years.
The asteroid that unleashed hell upon T.rex and co 66 million years ago is thought to have been between 10 and 15 kilometres wide. The new work, 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 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 are already very close to us.
Then there are all the asteroids smaller than a kilometre 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.
As if to underscore the potential for a sneak attack, the 70-metre-wide asteroid 2023 DZ2 passed between the Earth and the Moon back in March. Astronomers only spotted it a month beforehand.
Had it hit the Earth instead, it could have levelled a city. This close call came just two months after a truck-sized asteroid dubbed 2023 BU came within 3,600 kilometres of the southern tip of South America. That's ten times closer than some of our communications satellites. It was discovered less than a week before it buzzed by us.
Such asteroids don't even have to strike the planet's surface to inflict significant harm. “Objects as small as 50 metres can cause an airburst that is really devastating over a local area,” Bland says.
In February 2013 a 13-metre object exploded in the atmosphere above Chelyabinsk in Russia. Almost 1,500 people were injured and more than 7,000 buildings damaged. The total cost of repairs came to around £26 million.
Since then, astronomers have been ramping up their search efforts accordingly. Last year the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) project became the first survey capable of searching the entire dark sky every 24 hours for near-Earth objects (NEOs) that could pose a future impact hazard to Earth.
The upcoming Vera C. Rubin Observatory in Chile also reached a significant construction milestone in May this year with the completion of the telescope structure. It's now ready to be integrated with the telescope's 3,200-megapixel camera, the largest digital camera ever built.
Astronomers hope to start using it to survey the sky in October 2024. “It will give us a really interesting new look at this population of small asteroids,” Bland says, through a combination of “a powerful telescope, a large area survey and rapid, repeated coverage.”
Slightly further down the line, NASA hopes to launch its NEO Surveyor satellite in 2028. It should discover tens of thousands of newNEOswith diameters as small as 30metres.
How could Earth protect itself from an asteroid sneak attack?
So, what happens if one of these projects turns up an asteroid on a direct hit trajectory? “Asteroid impacts are one of the few natural disasters that can be prevented through human action,” note Fuentes-Muñoz and his colleagues in their paper.
NASA registered a significant breakthrough in 2022 when its Double Asteroid Redirection Test (DART) mission slammed a fridge-sized impactor into the asteroid Dimorphos.
The collisions successfully altered Dimorphos's orbit around a second asteroid called Didymos by 32 minutes. A triumph given that NASA's threshold for success was set at just 73 seconds. Perhaps in future we could knock a threatening asteroid off course in a similar manner.
At the time, NASA's Administrator Bill Nelson said that the success of DART “shows that NASA is trying to be ready for whatever the universe throws at us.”
Completing the catalogue of smaller potential threats would be an equally big step in the right direction.
About our expert, Prof Phil Bland
Phil is John Curtin Distinguished Professor at Curtin University’s School of Earth and Planetary Sciences.
His work is focussed on studying primitive meteorites to explore the origin and early evolution of the Solar System and understanding asteroid and cometary impacts.
He has had papers published in the journals Nature Astronomy, Meteoritics And Planetary Science and Proceedings of the National Academy of Sciences of the United States of America.
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