Apophis Cratering Experiment

Apophis will be one of the best studied of all asteroids due to the long visit of OSIRIS-APEX in 2029 and 2030. Here, we define a mission concept to leverage the capabilities OSIRIS-APEX as an observer and perform a cratering experiment at Apophis with an independent impactor spacecraft.

Apophis is very likely a rubble pile formed from reaccumulated debris following the disruption of a larger parent asteroid in the Main Belt and should be a generic representative of rubble pile formation and evolution. This is possibly a different formation and evolution than experienced by the target of the DART experiment – Dimorphos, which itself was a satellite of a larger asteroid. It probably formed from mass shedding events from its primary which may involve very gradual accretion.

Rubble pile asteroids have been targets of artificial cratering experiments, where Hayabusa2 Small Carry-on Impactor (SCI) created a large ~14m crater on asteroid Ryugu, and OSIRIS-REx created a nearly 10m crater on Bennu using its sampling mechanism and thrusters. The DART spacecraft impacted the asteroid Dimorphos with enough energy to likely significantly deform its shape.

Here, we propose a mission to impact Apophis, impart a measureable Delta-V, and make a larger and deeper crater than previous efforts. A 65kg impactor impacting Apophis at 7km/s will make a crater between 20-50m in diameter based on best knowledge of crater formation derived from the findings of SCI. This would result in an excavation of 2-8m deep – well below the depths previously explored and into the depths where crater morphology suggested increased strength at Bennu and Ryugu.

For the nominal mass of Apophis with simple momentum transfer (Beta=1), the resulting Delta-V would be 0.01mm/s. While incredibly small, it is ~2.5x larger than the formal 1-sigma tracking uncertainties for OSIRIS-REx at Bennu, owing to its long baseline of study and highly capable radio science package. The momentum enhancement expected in the cratering process should increase the Delta-V.

The combined knowledge of the mass of the target owing to OSIRIS-APEX and the measured Delta-V directly reports on the efficiency of momentum transfer during the cratering collision – the Beta parameter.

Owing to the importance of OSIRIS-APEX mapping and orbiting of Apophis for the interpretation of a cratering experiment, an impact after the completion of those studies would be ideal. Thus, an ideal impact time is after November 2030. This allows for a wide range of launch opportunities even some that are after the Apophis Earth flyby.

Notably, this experiment leverages the science instruments from OSIRIS-APEX entirely, requiring only key instrumentation for the impactor spacecraft survival and navigation. The large desired mass may also allow additional instrumentation to fly along in deep space for technology maturation purposes.