Speaker
Description
The physical properties of potentially hazardous small bodies are critical for planetary defense studies. The Sq-type asteroid (99942) Apophis, an Aten asteroid with an Earth-crossing orbit, will pass within ~32,000 km of Earth on Friday April 13, 2029. This close encounter could induce surface alterations of Apophis, such as landslides and mass wasting, due to gravitational interactions with Earth. NASA’s OSIRIS-APEX will visit Apophis a few weeks after the closest approach of the asteroid to the Earth to observe these potential surface changes after the Earth encounter and will stir up surface regolith using thrusters. ESA’s RAMSES will visit the asteroid starting from a few weeks before encounter to measure its initial properties and how they change during the closest approach (Michel et al., this conference). Other spacecraft may also participate in investigations of Apophis during its Earth encounter.
We here propose conducting low-energy multi-impact experiments on Apophis after its Earth encounter, using a payload onboard a spacecraft performing a rendezvous with Apophis, to further study its physical and material properties of Apophis, such as surface regolith cohesion, boulder strength, space weathering effects, and regional variations of these properties. The mechanism for launch of the projectiles on the payload can take advantage of technological heritage from ALE's human-made shooting star satellites (https://star-ale.com/en/technology/). As demonstrated by Hayabusa2’s small carry-on impactor experiment (Arakawa et al., 2020; Kadono et al., 2020), impact experiments are invaluable for studying the surface properties of small bodies. The proposed impacts (up to 10–20), with low kinetic energy (~50-100 J per projectile), are about 1/4-1/2 of that of JAXA’s Hayabusa2 sampler (Sawada et al., 2017; Thuillet et al., 2019; Tachibana et al., 2022) and are expected to make ~10-cm craters on regolith or chip off boulders. We also note that these low energy impacts will not alter the Apophis’s orbit.
The proposed impact experiments will provide us with additional opportunities for active/dynamic exploration of Apophis, complementing the effect of Earth’s tidal forces and OSIRIS-APEX’s thruster experiment. We believe that low-energy multi-impact experiments will provide unique scientific insights and enhance the overall value of all space missions to Apophis.