Near-Earth asteroid Apophis is a potentially hazardous asteroid that will safely pass close to Earth on April 13, 2029. It will come about 20,000 miles (32,000 kilometers) from our planet’s surface — closer than the distance of many satellites in geosynchronous orbit (about 22,236 miles, or 36,000 kilometers, in altitude).

Apophis is a relic of the early solar system. It’s made of leftover “raw material” that was never part of a planet or moon. Apophis has a mean diameter of 1,115 feet (340 meters), and a long axis that is at least 1,480 feet (450 meters) long.

When it was discovered in 2004, it appeared Apophis might impact Earth in either 2029, 2036, or 2068. Since then, astronomers have closely watched Apophis using optical telescopes and ground-based radar, allowing its orbit to become better understood. Based on this data, NASA is now confident that there is no risk of Apophis impacting Earth for at least 100 years.

Even though Apophis does not pose any immediate risk to Earth, an asteroid of its size passing so close to our planet is a very rare event. Scientists across the globe are excited to use this opportunity to study Apophis in detail. 

Observatories around the world and in space will observe asteroid Apophis’ historic close approach to better understand its physical properties. NASA also organizes the International Asteroid Warning Network (IAWN), which will coordinate Earth-based telescopic observing campaigns before and around the time of the asteroid’s flyby with our planet.

NASA has redirected a spacecraft to rendezvous with Apophis shortly after the asteroid’s 2029 Earth close-approach. After successfully completing its mission to gather a sample of asteroid Bennu and bringing it to Earth in September 2023, NASA’s OSIRIS-REx was sent to study Apophis. The spacecraft was renamed OSIRIS – APophis EXplorer (OSIRIS-APEX), and it’s on its way to meet up with its new target.

The European Space Agency, ESA, also is sending a spacecraft to study Apophis. The Rapid Apophis Mission for Space Safety (Ramses), will rendezvous with the asteroid and accompany it through its close flyby of Earth in 2029.

Apophis also will be visible to observers on the ground in the Eastern Hemisphere, weather permitting, without the aid of a spacecraft, telescope or even binoculars.

What Will Happen in 2029

On April 13, 2029, Apophis and Earth, each following its own orbit around the Sun, will pass each other at a close-approach distance of only 20,000 miles (36,000 kilometers). There is no danger to Earth, to anyone or anything living on it, or to astronauts or satellites in space. But the event is an amazing and totally unprecedented opportunity to learn much more about Apophis and similar near-Earth asteroids. An asteroid this large passes this close to Earth only every few thousand years on average, so it’s likely that an event like this has not happened at any time in recorded human history. Without a doubt this is the first time it’s happened when humans have had the technology to observe it.

The most important thing happening in this event is that Apophis will be pulled, twisted, stretched, and squeezed by the gravity of Earth as it goes by, in a way that happens only during a very close encounter. The overall pull will change Apophis’s orbit around the Sun, making the orbit slightly larger and giving it a longer orbital period. The twist will very probably change the way Apophis rotates, speeding up or slowing down its spin and changing its orientation. And the stretching and squeezing  may possibly cause some small landslides or other movement of surface material on the asteroid, most likely in places that are already steeply sloped. Exactly how Apophis responds to these disturbances will depend on its internal structure and the materials it’s composed of. So by observing and measuring those responses, scientists will be able to work backwards and figure out what is going on inside the asteroid.

Making those observations and measurements will take a worldwide effort from astronomers, planetary scientists, and spacecraft engineers. Earth-based telescopes will be recording Apophis’s path and measuring how its brightness changes as it rotates in the sunlight, to accurately determine the orbit and spin changes. Precisely timed radar echoes will reveal the asteroid’s shape as well as its changing orientation in space. And cameras, spectrographs, and other instruments on spacecraft, including NASA’s OSRIS-APEX and ESA’s Ramses spacecraft, will make high-resolution observations, measuring the detailed gravity field around Apophis and looking for any surface movements.

With these observations, we will have a greater understanding of near-Earth asteroids and the stories they tell about the history of Earth and our solar system.