Speaker
Description
Keywords: Apophis, OSIRIS-APEX
The OSIRIS-APEX mission will repurpose the OSIRIS-REx spacecraft to study Apophis, rendezvousing shortly after the asteroid’s close approach to Earth on 13 April 2029 [1-3]. The mission will produce and release many data products. We highlight here some that will be of particular interest to the planetary defense community.
- Shape model: We expect to produce a global shape model at 25 cm horizontal spacing or better, with vertical precision of a few centimeters.
- Mass and gravity field: We expect to measure the mass to better than 1% accuracy and the gravity to 2nd degree and order terms. At Bennu, the target asteroid of the previous mission, the orbits of particles that had spontaneously ejected from the surface were used to probe the gravity field to higher terms [4,5]. Thus, if ejected particles also orbit Apophis, the gravity field estimate will likely be better.
- Density of near-surface material: By observing the response of surface material to the spacecraft’s maneuvering thrusters, we will likely be able to estimate the mechanical properties. In addition, APEX maps of surface wasting features may constrain material strength and density.
- Thermal properties: APEX will observe the infrared spectrum of Apophis from a wide variety of viewing directions (times of day and night). These data will be used to map thermal inertia of the surface and to compare with ground-based observations.
- Yarkovsky acceleration: The Yarkovsky acceleration of Apophis has been measured using extensive ground-based radar and stellar occultation observations [6]. The close Earth encounter will change the Yarkovsky acceleration, as it changes the orbit and rotation state. APEX will re-measure the Yarkovsky acceleration to an accuracy of 4% of its current value in the planned campaign, or to 0.1% if observations can be extended an additional 4 months. This accuracy likely will not be possible from ground-based measurements until 2050. The updated Yarkovsky measurement will allow us to test models of the physical process, as well as improve our knowledge of the orbit of Apophis.
- APEX will produce spectral maps to understand surface heterogeneity.
References.
[1] DellaGiustina, D. N. et al. (2023) Planet. Sci. J. 4, 198. [doi:10.3847/PSJ/acf75e\
[2] Roberts, J. H. et al. (this meeting).
[3] Polit, A. T. et al. (this meeting).
[4] Hergenrother, C. W. et al. (2020) JGR Planets 125, e2020JE006381. doi:10.1029/2020JE006381
[5] Chesley, S. R. et al. (2020) JGR Planets 125, e2019JE006363. doi:10.1029/2019JE006363
[6] Farnocchia, D. and Chesley, S. R. (2022) Apophis T-7 Years workshop, abstract #2007.
https://ui.adsabs.harvard.edu/abs/2022LPICo2681.2007F