In five years, as the asteroid Apophis, dubbed the ‘God of Chaos’, passes close to Earth, scientists predict that the planet’s gravity could trigger “astroquakes” on the asteroid’s surface and possibly change its surface.
Since Apophis was first discovered in 2004, astronomers have closely monitored its trajectory. Early estimates suggested a 2.7 percent chance of impact in 2029, but recent studies have reduced the risk to nearly zero — about one in two billion.
A team led by Ronald-Louis Ballouz, an asteroid scientist at the Johns Hopkins University Applied Physics Laboratory, explored the effects of Earth’s gravity on Apophis as it passes within 19,000 miles of our planet. Their research indicates that Earth’s gravitational pull could induce violent tremors, potentially shaking the asteroid like an earthquake.
Apophis, which is scheduled to fly by Earth on April 13, 2029, is a massive ‘city-killer’ roughly the size of the Empire State Building. If it were to collide with Earth, the impact would release the equivalent of dozens or even hundreds of nuclear bombs, devastating a city and its surrounding areas.
While such an impact wouldn’t obliterate the planet, the destruction could extend for hundreds of miles, wiping out everything in its path.
Apophis, a peanut-shaped space rock measuring 1,230 feet (375 meters) across. Apophis is classified as a “potentially hazardous” object and was named after Apep, the Egyptian serpent god of darkness and disorder, earning it the nickname “God of Chaos”. As it approaches Earth, the asteroid will move within geostationary orbit and be visible to the naked eye.
Asteroids like Apophis typically have weathered surfaces due to constant bombardment by meteoroids — a process known as space weathering. However, astronomers have noticed that asteroids that pass close to planets often lack this weathered appearance.
Ballouz feels that Earth’s gravity might strip away the outer layers of these asteroids. The team created computational models of Apophis to test their theory and simulated its flyby while tracking any physical changes. Their findings suggest that Earth’s gravity could induce two main effects on the asteroid.
First, gravitational tidal forces — caused by the uneven pull of Earth — could cause Apophis to experience tremors, much like an earthquake. These shakes are expected to begin about an hour before the asteroid’s closest approach and continue for some time afterward. While the exact intensity is uncertain, Ballouz believes the shaking could be strong enough to dislodge boulders and eject rocks into space.
Second, Earth’s gravity could alter the asteroid’s rotation. Unlike planets, asteroids like Apophis tumble erratically through space. The flyby may disrupt its tumbling motion, triggering landslides over thousands of years that would expose fresh layers beneath the asteroid’s surface.
Both of these processes would gradually reshape Apophis, which is believed to be around four billion years old.
The research has been published on the arXiv preprint database and accepted for future publication in the Planetary Science Journal. If confirmed, the study could offer new insight into why some asteroids that pass close to planets show little evidence of space weathering.
Ballouz and his team are awaiting confirmation of their findings from NASA’s OSIRIS-APEX mission, which will rendezvous with Apophis during its 2029 flyby. The spacecraft will spend 18 months studying the asteroid, documenting any changes it undergoes due to Earth's gravitational influence.
As for the risk of Apophis colliding with Earth in the near future, according to recent Earth is safe for at least the next century. However, to prepare for the possibility of another ‘city-killer’ asteroid, NASA's Planetary Defense Coordination Office is actively developing methods to deflect or destroy potentially dangerous asteroids before they reach Earth.