The “city-killer” asteroid Apophis could be nudged onto a collision course with Earth by another asteroid before it flies past our planet in 2029
A new study highlights a small but overlooked possibility that the asteroid Apophis, also known as the “God of Chaos,” could collide with Earth during its extremely close approach in 2029. While the odds of such a collision are more than one-in-a-billion, we won’t know for sure if it’s possible for another three years.
Apophis is a peanut-shaped asteroid approximately 1,100 feet (340 meters) wide, about the size of the Eiffel Tower. Though it isn’t large enough to be considered a “planet killer,” it is still big enough to devastate a city and potentially cause global climate effects. It was discovered in 2004 and was named after Apep, the Egyptian god of darkness and disorder, hence its nickname, the “God of Chaos.”
When Apophis was first identified, astronomers predicted that it would pass very close to Earth on April 13, 2029, which raised concerns about a possible collision. However, further observations showed that the asteroid would pass safely, at a distance of less than 20,000 miles (32,000 kilometers), which is less than one-tenth the distance between Earth and the moon. Still, it may come close to some of Earth’s most distant satellites.
Despite this, large asteroids like Apophis could be knocked off course by collisions with smaller asteroids, similar to how NASA’s DART mission successfully altered the course of the asteroid Dimorphos in 2022 by crashing a spacecraft into it. Researchers have previously warned that Apophis could face such a situation over the next five years, potentially putting it on a collision course with Earth.
In a new study published on August 26 in The Planetary Science Journal, astronomer Paul Wiegert, an expert in solar system dynamics from Western University in Canada, assessed the likelihood of this scenario. He found that although it’s extremely unlikely, the possibility of Apophis being knocked off course and hitting Earth still exists.
In March, Wiegert co-authored another study that looked at the chances of Apophis being deflected by any known asteroids, concluding that there was “zero chance” of that happening. However, the researchers warned that an undiscovered asteroid could still potentially collide with Apophis.
In his new research, Wiegert used computer models to estimate the likelihood of an undiscovered asteroid—either too small or too close to the sun to be detected—colliding with Apophis in the next five years. The models showed that the chance of this happening is less than one-in-a-million, and the odds of such a collision significantly changing Apophis’ path before 2029 are less than one-in-a-billion, Wiegert wrote.
Even if an unknown asteroid were to hit Apophis, it doesn’t necessarily mean the asteroid would be pushed closer to Earth. In fact, it could be deflected further away, which makes the actual chances of a collision even lower.
However, we won’t know for certain if Apophis’ trajectory has changed until 2027, when the asteroid reappears after being too close to the sun to observe. At that time, astronomers will be able to more accurately assess whether any course changes have occurred before its 2029 flyby, according to Wiegert.
Beyond 2029, Apophis will continue to make close approaches to Earth, as it has in the past, including in 2021. Particularly close encounters are predicted for 2051, 2066, and 2080, but current models suggest that Apophis poses no risk to Earth for at least the next 100 years.
After 2029, scientists will learn more about Apophis’ future trajectory when NASA’s OSIRIS APEX spacecraft, which previously studied asteroid Bennu, flies past Apophis following its own flyby of Earth.
