NASA’s OSIRIS-APEX mission is giving an already successful spacecraft a second life by sending it to study the near-Earth asteroid Apophis. The spacecraft originally flew as OSIRIS-REx, which collected rocks and dust from asteroid Bennu and delivered them to Earth in 2023; because the spacecraft remained healthy and had fuel available, NASA redirected it toward a new target and renamed the mission OSIRIS-APEX (OSIRIS–APophis Explorer).
On April 13, 2029, the roughly 1,115-foot-wide (340 m) Apophis will safely pass only about 20,000 miles (32,000 km) above Earth’s surface—closer than many geosynchronous satellites. Earth’s gravity is expected to alter the asteroid’s orbit and rotation and could trigger surface changes such as landslides or asteroid quakes.
OSIRIS-APEX will rendezvous with Apophis after this extraordinary encounter and spend about 18 months mapping its surface and studying its composition and structure with cameras, spectrometers, and a laser altimeter. Near the end of the investigation, the spacecraft will descend close to the surface and fire its thrusters to blow away loose rocks and dust, exposing material underneath for its instruments to examine.
The mission is particularly valuable for planetary defense because Apophis is an S-type, or stony, asteroid similar to many potentially hazardous near-Earth asteroids. By watching what happens when Earth’s gravity dramatically disturbs one of these objects, scientists can learn more about how asteroids are built, how their orbits and surfaces change, and how we might better understand and respond to an asteroid that actually threatens Earth someday.
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