In April 2029, asteroid Apophis will pass exceptionally close to Earth—at just 20,000 miles away, closer than many satellites. The encounter may trigger significant physical changes on the asteroid’s surface due to Earth’s gravitational pull, potentially causing landslides and tremors, according to a recent study. Apophis, a 340-meter, peanut-shaped asteroid named after the ancient Egyptian deity associated with chaos, is not expected to impact Earth. However, this flyby could offer scientists a unique opportunity to observe how gravitational forces affect small celestial bodies.

New Insights into Surface Alterations

The study, currently available on the arXiv preprint database, has been accepted for publication in The Planetary Science Journal. Asteroid scientist Ronald-Louis Ballouz from Johns Hopkins University Applied Physics Laboratory and his team conducted computational simulations of Apophis to predict the changes Earth’s gravity might induce. Ballouz notes that while meteoroids constantly weather asteroid surfaces in space, close planetary encounters can also alter an asteroid’s appearance. The gravitational pull from Earth is expected to disrupt Apophis’ surface by triggering tremors, lifting rocks, and creating visible patterns.

Predicted Surface Shifts and Landslides

The team’s models suggest that Apophis will experience surface tremors starting an hour before it reaches its closest approach to Earth, potentially dislodging boulders. Although Apophis’ own gravity is weak, this gravitational “shaking” could loft rocks briefly before they fall back, forming new surface features. Additionally, Apophis’ irregular rotation, or “tumbling,” might accelerate or slow down due to Earth’s gravitational influence. These shifts in tumbling could further destabilise rocks over time, potentially leading to gradual landslides that shape the asteroid’s surface over tens of thousands of years.

Future Observations with NASA’s OSIRIS-APEX Mission

Scientists hope to verify these findings when NASA’s OSIRIS-APEX spacecraft studies Apophis in 2029. Repurposed from its earlier mission to the asteroid Bennu, OSIRIS-APEX is set to examine Apophis’ chemical composition and surface features over an 18-month mission. This research could help solve longstanding questions about how gravitational encounters refresh asteroid surfaces, providing new insights into asteroid dynamics and planetary formation processes.