NASA’s Double Asteroid Redirection Test (DART): Mutual Orbital Period Change Due to Reshaping in the Near-Earth Binary Asteroid System (65803) Didymos

Nakano, Ryota; Hirabayashi, Masatoshi; Agrusa, Harrison F.; Ferrari, Fábio; Meyer, Alex J.; Michel, Patrick; Raducan, Sabina D.; Sánchez, Paul; Zhang, Yun

doi:10.3847/psj/ac7566

Cited by 22 publications

(33 citation statements)

References 50 publications

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“…The instantaneous torque on Dimorphos due to DART’s slightly off-centre impact 1 is also neglected as the corresponding change in Dimorphos’s rotation state is small compared to that arising from exciting Dimorphos’s eccentricity and libration by the impact 10 , 37 , 45 . Finally, the effects of reshaping and mass loss due to cratering and ejecta are also neglected, as these effects are expected to be smaller in magnitude than the current roughly 1 min uncertainty on the post-impact orbit period 46 and will remain poorly constrained until the Hera mission characterizes the Didymos system in 2027 (ref. 30 ).…”

Section: Methodsmentioning

confidence: 99%

Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos

Cheng

Agrusa

Barbee

et al. 2023

Nature

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The NASA Double Asteroid Redirection Test (DART) mission performed a kinetic impact on asteroid Dimorphos, the satellite of the binary asteroid (65803) Didymos, at 23:14 UTC on 26 September 2022 as a planetary defence test1. DART was the first hypervelocity impact experiment on an asteroid at size and velocity scales relevant to planetary defence, intended to validate kinetic impact as a means of asteroid deflection. Here we report a determination of the momentum transferred to an asteroid by kinetic impact. On the basis of the change in the binary orbit period2, we find an instantaneous reduction in Dimorphos’s along-track orbital velocity component of 2.70 ± 0.10 mm s−1, indicating enhanced momentum transfer due to recoil from ejecta streams produced by the impact3,4. For a Dimorphos bulk density range of 1,500 to 3,300 kg m−3, we find that the expected value of the momentum enhancement factor, β, ranges between 2.2 and 4.9, depending on the mass of Dimorphos. If Dimorphos and Didymos are assumed to have equal densities of 2,400 kg m−3, $${\beta =3.61}_{-0.25}^{+0.19}(1\sigma )$$ β = 3.61 − 0.25 + 0.19 ( 1 σ ) . These β values indicate that substantially more momentum was transferred to Dimorphos from the escaping impact ejecta than was incident with DART. Therefore, the DART kinetic impact was highly effective in deflecting the asteroid Dimorphos.

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Section: Methodsmentioning

confidence: 99%

Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos

Cheng

Agrusa

Barbee

et al. 2023

Nature

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“…The reshaping of Dimorphos may induce perturbations to the mutual orbit. To investigate this possibility, a finite element method (FEM) approach was used to simulate the mutual dynamics of the Didymos system, by accounting for the reshaping of Dimorphos during the DART impact (Nakano et al 2022). The model uses the shape models from the Didymos system DRA data (Section 2).…”

Section: Reshaping-induced Mutual Orbit Perturbationmentioning

confidence: 99%

Predictions for the Dynamical States of the Didymos System before and after the Planned DART Impact

Richardson¹,

Agrusa²,

Barbee³

et al. 2022

Planet. Sci. J.

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NASA’s Double Asteroid Redirection Test (DART) spacecraft is planned to impact the natural satellite of (65803) Didymos, Dimorphos, at around 23:14 UTC on 2022 September 26, causing a reduction in its orbital period that will be measurable with ground-based observations. This test of kinetic impactor technology will provide the first estimate of the momentum transfer enhancement factor β at a realistic scale, wherein the ejecta from the impact provide an additional deflection to the target. Earth-based observations, the LICIACube spacecraft (to be detached from DART prior to impact), and ESA’s follow-up Hera mission, to launch in 2024, will provide additional characterizations of the deflection test. Together, Hera and DART comprise the Asteroid Impact and Deflection Assessment cooperation between NASA and ESA. Here, the predicted dynamical states of the binary system upon arrival and after impact are presented. The assumed dynamically relaxed state of the system will be excited by the impact, leading to an increase in eccentricity and a slight tilt of the orbit, together with enhanced libration of Dimorphos, with the amplitude dependent on the currently poorly known target shape. Free rotation around the moon’s long axis may also be triggered, and the orbital period will experience variations from seconds to minutes over timescales of days to months. Shape change of either body, due to cratering or mass wasting triggered by crater formation and ejecta, may affect β, but can be constrained through additional measurements. Both BYORP and gravity tides may cause measurable orbital changes on the timescale of Hera’s rendezvous.

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“…We also note that the global shape of Dimorphos may also be immediately altered by the DART impact itself . In addition to affecting the system dynamics (Nakano et al 2022), these processes will create a unique challenge in discerning the various surface refreshment mechanisms upon Hera's arrival.…”

Section: Discussionmentioning

confidence: 99%

Rotation-induced granular motion on the secondary component of binary asteroids: Application to the DART impact on Dimorphos

Agrusa

Ballouz

Meyer

et al. 2022

A&A

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Context. NASA’s Double Asteroid Redirection Test (DART) mission will kinetically impact Dimorphos, the secondary component of the Didymos binary asteroid system, which will excite Dimorphos’s dynamical state and lead to significant libration about the synchronous state and possibly chaotic non-principal axis rotation. Although this particular outcome is human caused, many other secondary components of binary systems are also prone to such exotic spin states. Aims. For a satellite in an excited spin state, the time-varying tidal and rotational environment can lead to significant surface accelerations. Depending on the circumstances, this mechanism may drive granular motion on the surface of the secondary. Methods. We modeled the dynamical evolution of a Didymos-like binary asteroid system using a fully coupled, three-dimensional simulation code. Then, we computed the time-varying gravitational and rotational accelerations felt over the entire surface resulting from the secondary’s perturbed dynamical state. Results. We find that an excited spin and orbit can induce large changes in the effective surface slope, potentially triggering granular motion and surface refreshment. However, for the case of the DART impact, this effect is highly dependent on many unknowns, such as Dimorphos’s detailed shape, bulk density, surface geology, and the momentum transferred. Aside from the Didymos system and the DART mission, this effect also has important implications for binary systems in general.

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NASA’s Double Asteroid Redirection Test (DART): Mutual Orbital Period Change Due to Reshaping in the Near-Earth Binary Asteroid System (65803) Didymos

Cited by 22 publications

References 50 publications

Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos

Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos

Predictions for the Dynamical States of the Didymos System before and after the Planned DART Impact

Rotation-induced granular motion on the secondary component of binary asteroids: Application to the DART impact on Dimorphos

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