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Earth is probably safe from a killer asteroid for 1,000 years

No asteroid larger than a kilometer is likely to hit us in that time frame, says a new study. But smaller ones could still pose a risk.

an animation with a stationary star icon in the center to represent the Earth with circles and squares moving around it.
In this NEOWISE timelapse, green circles represent near-Earth objects, yellow squares represent comets, and gray dots represent all other asteroids.NASA/JPL-Caltech/PSI

Put your feet up for a millennium. That’s the finding of a new study that tracked how many large asteroids have a chance of hitting Earth in the next 1,000 years. The answer? Probably none of them.

“It’s good news,” says Oscar Fuentes-Muñoz from the University of Colorado, Boulder, in the US, who led the study, accepted for publication in The Astronomical Journal. “As far as we know, there’s no impact in the next 1,000 years.”

About 66 million years ago, it’s believed, the dinosaurs were wiped out in part by the impact of a 10-kilometer-wide asteroid, killing most land-based life in a matter of hours as molten debris rained down. The impact also blanketed our planet in dust and soot, blocking out the light of the sun and causing a decades-long winter.

Fortunately, we know that such impacts are rare. NASA has previously estimated that a civilization-ending event such as this, resulting from an asteroid larger than a kilometer in size, befalls our planet only once every few million years. The only problem was we couldn’t quite rule it out for the time being.

Fuentes-Muñoz and his colleagues, however, think they’ve done so. NASA’s catalogue of asteroids that are near Earth and larger than a kilometer in size is now thought to be 95% complete, with nearly 1,000 such objects known to exist. Tracking the orbits of these asteroids allows astronomers to predict their paths up to about a century from now, taking into account factors such as the gravity of Jupiter. 

In this latest study, the researchers used a different method, modeling when the asteroids were expected to come near Earth in their orbit and pushing those estimates up to 1,000 years into the future.

“We came up with a less computationally intense approach to take a peek at a longer time interval,” says Davide Farnocchia from NASA’s Center for Near Earth Object Studies at the Jet Propulsion Laboratory in California, a coauthor on the study. By identifying “the fraction of the orbit that can bring the object close to Earth,” the team was able to model impact risks much farther out than has been possible with other methods.

Of the asteroids modeled by the team, the one with the highest risk of impact was called 1994 PC1. That object, a stony asteroid about a kilometer wide, was found to have a 0.00151% chance of passing within the orbit of the moon in the next 1,000 years. While incredibly small, this was 10 times higher than the risk posed by any other asteroid.

“It’s still not likely that it’s going to collide,” says Fuentes-Muñoz. “But it will be a very good scientific opportunity, because it’s going to be a huge asteroid that’s very close to us.”

The study was partly inspired by a request from the US Congress, which in 1998 asked NASA to catalogue 90% of the near-Earth asteroids larger than a kilometer in size. “In general, asteroid impacts capable of causing significant damage to Earth are extremely unlikely,” says Farnocchia. “Just in case, we are doing our due diligence.”

Áine O’Brien from the University of Glasgow, a planetary scientist who tracks incoming meteors and who was not involved in the study, says it is good to see simulations predicting large-asteroid impacts beyond 100 years. “The fact that they can now extend that period is a good thing,” she says. 

However, smaller asteroids, which are much more plentiful, still pose a risk to Earth. In 2013, for example, a 20-meter-wide meteor exploded above Chelyabinsk in Russia, injuring more than 1,000 people and shattering windows, despite its small size. “Smaller objects still cause a lot of damage,” says O’Brien.

Efforts are being made to track smaller asteroids. For asteroids larger than 140 meters across, which could destroy a city, NASA’s catalogue is about 40% complete, says Fuentes-Muñoz. “But it depends on how many there are, which is really uncertain,” he says. “We’re not sure. But there’s hope that new surveys of the sky will give us a much higher completeness rate.” The Vera Rubin Observatory in Chile, set to begin a broad survey of the solar system next year, will contribute important findings.

For the time being, however, it looks as though civilization as a whole can rest easy. “At some point, there’ll be something heading this way,” says O’Brien. But that point, it seems, is unlikely to come before the year 3000.

Correction: We have updated the story post-publishing to better reflect the lack of definitive certainty associated with these findings, and amended the impact risk of 1994 PC1 from 0.000151% to 0.00151%.

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