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 0.000151% 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.”