A team of astronomers believe that our planet’s gravitational pull could alter the surface of Apophis, a near-Earth asteroid (NEA) set to make a close approach to Earth in five years’ time.
Apophis is currently 1.97 astronomical units from Earth—or about twice as far from Earth as our planet is from the Sun. But in April 2029, the asteroid will swing right by our planet, and a team of researchers believes that the encounter will cause landslides and quakes on the smaller rock. The team’s findings are set to publish in The Planetary Science Journal and are currently hosted on the preprint server arXiv.
“The 2029 encounter will induce short-term tidally-driven discrete seismic events that lead to high-frequency surface accelerations that reach magnitudes similar to Apophis’ gravity, and that may be detectable by modern seismometers,” the researchers wrote in the paper.
Space scientists are paying close attention to Apophis’ April 13, 2029 flyby (and yes—April 13, 2029 is a Friday). When it makes its nearest pass, the 1,100-foot-wide (335-meter-wide) asteroid will be within 24,000 miles (38,625 kilometers) of our planet’s surface—roughly ten times closer than the Moon’s usual distance in its orbit through our cosmic neighborhood.
That proximity to Earth means that Apophis will be altered by the gravitational pull of our planet, the same force that keeps the Moon in orbit around us. But Apophis is much smaller than the Moon, and will be closer to Earth, so Earth’s gravity will have a more extreme impact on the asteroid. This is the same force that causes stress and fracture marks on the surface of moons like Uranus’ Miranda, and raises questions about the stability of our own Moon, which will need to have a steady enough surface for NASA to safely land astronauts during the upcoming Artemis 3 mission.
“We also find there will be a significant change in Apophis’ tumbling spin state that could lead to longer-term surface refreshing in response to tumbling-induced surface slope changes,” the team wrote, adding that such a mechanism could refresh the surfaces of other asteroids like Apophis.
This aspect of the team’s finding is compelling, because scientists can learn plenty from the interiors of asteroids. These hidden asteroid bits can reveal both the origins of the space rocks, but also the history of our solar system and beyond. Organic molecules in asteroids can hint at sources of life’s building blocks, and the metals in the rocks can indicate the extreme cosmic interactions that caused the asteroid to form. Asteroid interiors can offer layers of more ancient information about the content of a space rock and the way it interacts with its local environment in space, and explain why some objects—like the peculiar interstellar interloper ‘Oumuamua—accelerate like spaceships.
Like ‘Oumuamua, Apophis is expected to swing by Earth. In all-but-the-slimmest likelihood, Apophis is not a threat to life on Earth. A lot would have to go wrong for the asteroid’s trajectory to change in a way that would put it on a collision course with our planet.
That said, objects around Apophis’ size hit our planet once every 80,000 years or so, and their impacts cause grievous damage in the immediate vicinity of their impact, but also can cause chilling changes to the climate. A 2021 NASA analysis found that Apophis’ trajectory won’t threaten our planet—meaning not even the slightest chance of harm—for at least a century.
Earlier this year, space companies including Blue Origin proposed missions to capitalize on the asteroid’s brush with Earth. After all, space agencies are essentially cosmic doctors making home visits; it’s very rare—and much cheaper—when the patient comes to you.
But forget mission concepts, for a moment—there’s already one mission heading off to rendezvous with Apophis. NASA’s OSIRIS-APEX mission is on its way to the asteroid to better understand how the rock may be transformed by its close encounter with our planet.
If it were to hit Earth—which it won’t—Apophis’ footprint would fit neatly inside Manhattan’s Battery Park (as shown above). The last significant asteroid to reach Earth was the Chelyabinsk fireball—a rock about the size of a small building that exploded over Russia in 2013. The explosion released energy equivalent to approximately 500 kilotons of TNT, causing a bright flash and a powerful shockwave. The Chelyabinsk asteroid was just 66 feet across (20 meters)—about 17 times smaller than Apophis.
Still, that comparison showcases the potential hazard of near-Earth asteroids, and the reason agencies like NASA watch them so closely. Though by the recent team’s measure, Earth will cause much more havoc on Apophis than the asteroid will on our planet.