Speaker
Description
The OSIRIS-APEX (Origins, Spectral Interpretation, Resource Identification, and Security–Apophis Explorer) mission will approach and rendezvous with asteroid (99942) Apophis in the spring of 2029, just after its close approach to Earth (DellaGiustina et al., 2023). APEX has three primary mission goals. The first is to study the processes that drive the evolution of small asteroids, including tidal effects from close encounters with terrestrial planets. Apophis will come within 0.1 lunar distances of Earth (Farnocchia & Chodas, 2021). This encounter is expected to result in potentially dramatic tidal deformation (Dotson et al., 2022). Additionally, APEX proximity operations will help to reveal changes in the rotation state. Indeed, by comparing the spin states of Apophis before and after Earth close-approach, APEX will be able to constrain the internal density distribution, an important property needed to inform impact threat assessments (NASA, 2023).
The second goal is to determine the characteristics of a “stony” (S-complex) object to study physical and dynamical evolution, including any previous Earth encounters. The mission will obtain images across a broad range of wavelengths (0.4–100 µm) and lidar ranging data to produce meter-scale maps and centimeter-scale global morphology. Radio science will be used to determine the mass of Apophis and the degree-2 gravity field, providing information about mass, interior structure, and surface properties. Taken together, these measurements will constrain the mechanical structure of Apophis including surface heterogeneities – key properties that help inform planetary defense strategies (NASA, 2023).
The third goal is to examine the properties of a potentially hazardous S-complex asteroid to help inform planetary defense knowledge and strategies. APEX will measure the near-surface strength of Apophis through the Spacecraft Thruster Investigation of Regolith (STIR) maneuver. The spacecraft will approach Apophis’s surface, then back away using its thrusters, which will excavate material. The response of the surface will provide constraints on material strength, porosity, and bulk density — key properties controlling momentum transfer efficiency for a kinetic deflection mission (Stickle et al., 2022).
Additionally, the rare close encounter of Apophis with Earth will provide excellent viewing conditions for many ground-based observatories. Comparing in situ rendezvous data from APEX with ground-based observations will enable synergistic analysis and calibration of datasets and improved higher-order science products. In particular, data returned by APEX will help to assess the accuracy of ground-based measurements of properties relevant to planetary defense. Thus, the Apophis close encounter and APEX mission present the opportunity for a globally coordinated planetary defense exercise using both ground- and space-based assets (Barbee et
al., 2021).
- Barbee, B. et al. (2021) BAAS, doi:10.3847/25c2cfeb.dc0c7b69.
- DellaGiustina, D. N. et al. (2023) Planet. Sci. J. 4, 198.
- Dotson, J.L. et al. (2022) Apophis Specific Action Team Report. SBAG, LPI.
- Farnocchia, D. and Chodas, P. W. (2021) Res. Notes AAS 5, 257.
- NASA Planetary Defense Strategy & Action Plan Working Group (2023),
NASA Planetary Defense Strategy and Action Plan,
https://go.nasa.gov/3UO2mmt - Stickle, A. M. et al. (2022), Planet. Sci. J.
3, 248.