Pre-Impact Thermophysical Properties and the Yarkovsky Effect of NASA DART Target (65803) Didymos

Benjamin Rozitis*, Simon F Green, Samuel L Jackson, Colin Snodgrass, Cyrielle Opitom, Thomas G Muller, Ulrich C Kolb, Steven R. Chesley, R. Terik Daly, Cristina A. Thomas, Andrew S. Rivkin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

The NASA DART (Double Asteroid Redirection Test) spacecraft impacted the
secondary body of the binary asteroid (65803) Didymos on 2022 September 26
and altered its orbit about the primary body. Before the DART impact, we
performed visible and mid-infrared observations to constrain the pre-impact
thermophysical properties of the Didymos system and to model its Yarkovsky
effect. Analysis of the photometric phase curve derives a Bond albedo of 0.07
± 0.01, and a thermophysical analysis of the mid-infrared observations
derives a thermal inertia of 320 ± 70 J m-2 K-1 s-1/2 and a thermal roughness of 40° ± 3° RMS (root-mean-square) slope. These properties are compatible with
the ranges derived for other S-type near-Earth asteroids. Model-to-measurement comparisons of the Yarkovsky orbital drift for Didymos derives a
bulk density of 2750 ± 350 kg m-3, which agrees with other independent
measures based on the binary mutual orbit. This bulk density indicates that
Didymos is spinning at or near its critical spin-limit at which self-gravity
balances equatorial centrifugal forces. Furthermore, comparisons with the
post-impact infrared observations presented in Rivkin et al. (2023) indicate
no change in the thermal inertia of the Didymos system following the DART
impact. Finally, orbital temperature simulations indicate that sub-surface
water ice is stable over geologic timescales in the polar regions if present.
These findings will be investigated in more detail by the upcoming ESA Hera
mission.
Original languageEnglish
JournalThe Planetary Science Journal
Publication statusAccepted/In press - 28 Jan 2024

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