Apophis in 2029: A Close Pass, and the Cascading Hazards of Asteroid Impacts

On Friday, April 13, 2029, the asteroid Apophis — officially 99942 Apophis, pronounced "uh-PAW-fiss," and named for the Egyptian god of chaos and destruction — will pass close to Earth. It is not expected to hit.

"Near-Earth Objects like Apophis represent a potential hazard to Earth, not just from the primary impact but also from hazards caused by a primary hazard or as part of a series of events." — Timothy Titus, research space scientist, U.S. Geological Survey

A near-Earth object

Near-Earth objects are small solar-system bodies, made mostly of the leftover building blocks of the solar system, whose orbits around the Sun bring them close to Earth. Apophis, about 340 meters across, is classed as a "potentially hazardous object" — big enough to do serious damage if it struck. Close passes by objects that size or larger are rare, happening every few thousand years or so.

Apophis will come within 31,860 kilometers of Earth — inside the orbit of geosynchronous satellites at 35,800 kilometers — but its path relative to them makes a collision unlikely.

A computer-simulated image of Apophis (right), from a hypothetical shape model. Orbit lines are to scale by diameter, but Apophis will not orbit: it will fly past, arriving from below the plane of geosynchronous orbit and leaving above it. U.S. Geological Survey

The U.S. Geological Survey is working with other federal agencies, industry, universities and international partners to characterize Apophis, prepare for the flyby, and develop ways to study and reduce the risks from other near-Earth objects. A Specific Action Team, with USGS taking part, was set up to:

1. identify and measure the effects of the flyby on Apophis;
2. judge how important measuring them is;
3. sort the effects by how detectable they are;
4. assess the risk to Earth of a spacecraft rendezvous with Apophis.

Apophis's approach relative to Earth, Moon and Sun, and the ring of geosynchronous satellites (teal), from the Specific Action Team report (Dotson and others, 2022)

Asteroids the size of Apophis are likely to be spotted, but much smaller ones may arrive with little or no warning.

"Preparedness is key. For the future, it's better to have a mitigation strategy in hand, rather than wait until there is an actual crisis to develop a plan." — Timothy Titus

Cascading hazards

An impact's effects depend on its size and location. The typical primary effects are earthquakes, tsunamis, blast waves and heat. Secondary and longer-term effects are much less studied — and they can reach far beyond the impact site, with consequences for global agriculture and public health that may need long-term monitoring. USGS brings its data on wildfires, volcanoes, landslides and water quality to model them.

These cascading hazards fall into two groups:

Both can cause regional or wider harm and long-lasting damage, threatening life, farming, transportation and property. As of 2025 they were not well understood, and USGS is working to change that.

From impact to cascade: the primary hazard at the center, secondary effects such as tsunamis, thermal radiation, blast winds and dust plumes around it, and further hazards — flooding, landslides, crop failure, wildfires — beyond. Modified from Titus and others (2023), U.S. Geological Survey

Studying asteroids up close

Knowing an asteroid's size, shape, composition and physical properties is vital for modeling an impact. Software from the USGS Astrogeology Science Center turns spacecraft data into shape models of asteroids such as Bennu, Eros and Itokawa. The OSIRIS-REx spacecraft imaged and sampled Bennu; after delivering its sample it was renamed OSIRIS-APEX and will visit Apophis after the 2029 flyby. USGS partners in many such missions, collecting, processing and archiving asteroid data for today and the future.

Sources

Based on Countdown to Apophis Close Approach—Cascading Hazards from Asteroid Impacts, U.S. Geological Survey Fact Sheet 2025–3028, USGS Publications Warehouse, citing Dotson and others (2022) and Titus and others (2023); a work of the United States government in the public domain.