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OSIRIS-APEX: An OSIRIS-REx Extended Mission to Asteroid Apophis
The Origins, Spectral Interpretation, Resource Identification, and SecurityâRegolith Explorer (OSIRIS-REx) spacecraft mission characterized and collected a sample from asteroid (101955) Bennu. After the OSIRIS-REx Sample Return Capsule released to Earthâs surface in 2023 September, the spacecraft diverted into a new orbit that encounters asteroid (99942) Apophis in 2029, enabling a second mission with the same unique capabilities: OSIRISâApophis Explorer (APEX). On 2029 April 13, the 340 m diameter Apophis will draw within âŒ32,000 km of Earthâs surface, less than 1/10 the lunar distance. Apophis will be the largest object to approach Earth this closely in recorded history. This rare planetary encounter will alter Apophisâs orbit, will subject it to tidal forces that change its spin state, and may seismically disturb its surface. APEX will distantly observe Apophis during the Earth encounter and capture its evolution in real time, revealing the consequences of an asteroid undergoing tidal disturbance by a major planet. Beginning in 2029 July, the spacecraftâs instrument suite will begin providing high-resolution data of this âstonyâ asteroidâadvancing knowledge of these objects and their connection to meteorites. Near the missionâs end, APEX will use its thrusters to excavate regolith, a technique demonstrated at Bennu. Observations before, during, and after excavation will provide insight into the subsurface and material properties of stony asteroids. Furthermore, Apophisâs material and structure have critical implications for planetary defense