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[MZZ45-02] Orbit period change induced by Dimorphos’s reshaping after the DART impactOrbit period change induced by Dimorphos’s reshaping after the DART impact
キーワード：DART, Dimorphos, Reshaping, Orbit perturbation
On September 26th, 2022, NASA’s Double Asteroid Direction Test (DART) spacecraft impacted Dimorphos, the secondary of the binary asteroid system (65803) Didymos [1]. The impact resulted in a reduction of the orbit period by 33 minutes [2, 3] and an estimated momentum transfer enhancement factor, β, of 2.2 to 4.9 for plausible ranges of physical properties of the system [4].
Just seconds before the impact, the DRACO instrument captured detailed images of Dimorphos’s surface, which appeared to be a rocky terrain covered with boulders, resembling a rubble-pile, similar to asteroids (101955) Bennu and (162173) Ryugu. If Dimorphos has a weak structure with low cohesive strength (i.e., typical of a rubble-pile), the DART impact could have modified Dimorphos’s intermediate axis (Y axis) by up to a few decameters, leading to an elongated shape [5]. The observed orbit period change (i.e., 33 min) could thus be a result of spacecraft momentum, ejecta recoil, and reshaping.
In this study, we generate hypothetical shape models of a reshaped Dimorphos and simulate the mutual dynamics after reshaping. Our simulations do not account for the momentum transfer by the DART impact as the reshaping and impact effects are independent to first order [6]. Figure 1 shows the orbit period change, ΔP, solely as a function of reshaping along the Y axis, ΔY. We find that the orbit period generally becomes shorter than the original orbit period without reshaping. More than 3 m of reshaping leads to an orbit-period change comparable to the required observation accuracy of 7.3 sec [7]. These preliminary results indicate that β, if thought to be the result of spacecraft momentum and ejecta recoil alone, could be overestimated. Careful assessment is thus necessary to properly interpret the measured orbit period change and determine β accurately.
We will present our updated analysis of the Dimorphos’s reshaping effect on the mutual orbit. Using the latest impact simulation results and ground-based observation data, we will statistically quantify the most probable effect of reshaping and decouple the reshaping-induced orbit period change from the observed orbit period change.
References
[1] Daly et al. 2023, Nature
[2] Thomas et al., 2023, Nature
[3] Scheirich & Pravec, 2022, AGUFM
[4] Cheng et al., 2023, Nature
[5] Raducan et al., 2023, PDC
[6] Nakano et al., 2022, PSJ
[7] Rivkin et al., 2022, PSJ
Just seconds before the impact, the DRACO instrument captured detailed images of Dimorphos’s surface, which appeared to be a rocky terrain covered with boulders, resembling a rubble-pile, similar to asteroids (101955) Bennu and (162173) Ryugu. If Dimorphos has a weak structure with low cohesive strength (i.e., typical of a rubble-pile), the DART impact could have modified Dimorphos’s intermediate axis (Y axis) by up to a few decameters, leading to an elongated shape [5]. The observed orbit period change (i.e., 33 min) could thus be a result of spacecraft momentum, ejecta recoil, and reshaping.
In this study, we generate hypothetical shape models of a reshaped Dimorphos and simulate the mutual dynamics after reshaping. Our simulations do not account for the momentum transfer by the DART impact as the reshaping and impact effects are independent to first order [6]. Figure 1 shows the orbit period change, ΔP, solely as a function of reshaping along the Y axis, ΔY. We find that the orbit period generally becomes shorter than the original orbit period without reshaping. More than 3 m of reshaping leads to an orbit-period change comparable to the required observation accuracy of 7.3 sec [7]. These preliminary results indicate that β, if thought to be the result of spacecraft momentum and ejecta recoil alone, could be overestimated. Careful assessment is thus necessary to properly interpret the measured orbit period change and determine β accurately.
We will present our updated analysis of the Dimorphos’s reshaping effect on the mutual orbit. Using the latest impact simulation results and ground-based observation data, we will statistically quantify the most probable effect of reshaping and decouple the reshaping-induced orbit period change from the observed orbit period change.
References
[1] Daly et al. 2023, Nature
[2] Thomas et al., 2023, Nature
[3] Scheirich & Pravec, 2022, AGUFM
[4] Cheng et al., 2023, Nature
[5] Raducan et al., 2023, PDC
[6] Nakano et al., 2022, PSJ
[7] Rivkin et al., 2022, PSJ