Heliocentric Effects of the DART Mission on the (65803) Didymos Binary Asteroid System

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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.

Section: Didymos System Heliocentric Orbit Changesmentioning

confidence: 99%

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

Richardson¹,

Agrusa²,

Barbee³

et al. 2022

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“…In the case of a binary system, there are two β values to be considered: a β value for Dimorphos, which has been the focus of DARTʼs investigation (Cheng et al 2023), and a heliocentric β value for the Didymos system, the momentum enhancement factor caused by the ejecta that escapes the binary system. A pre-impact analysis examined the range of possible heliocentric β values that could result from DARTʼs impact and demonstrated that the Didymos system would not be shifted onto a collision course with the Earth (Makadia et al 2022), although, a measure of the Didymos systemʼs deflection about the Sun potentially could be made in the future (Richardson et al 2022). A measurement of heliocentric β for the Didymos system has not yet been made; though, multiple high-quality stellar occultation observations obtained in 2022-2023, including detections of Dimorphos as the smallest object ever observed during an occultation campaign, may make such a measurement possible in the next few years (Makadia et al 2024).…”

Section: The Binary Didymos Systemmentioning

confidence: 99%

“…Pre-impact studies were important in establishing the methodologies to be applied to investigate the post-impact dynamics of the Didymos system and in considering a wide range of possible outcomes (Agrusa et al 2020(Agrusa et al , 2021Meyer et al 2021Meyer et al , 2023bAgrusa et al 2022;Makadia et al 2022;Richardson et al 2022). Overall, the DART kinetic impact test resulted in a small change to the dynamical state of the Didymos system that is generally consistent with pre-impact expectations, with the biggest surprises attributed to the flattened shape of Didymos compared to the radar-based model and the oblate pre-impact shape of Dimorphos (Richardson et al 2024).…”

Section: The Binary Didymos Systemmentioning

confidence: 99%

Achievement of the Planetary Defense Investigations of the Double Asteroid Redirection Test (DART) Mission

Chabot,

Rivkin,

Cheng

et al. 2024

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NASA's Double Asteroid Redirection Test (DART) mission was the first to demonstrate asteroid deflection, and the mission's Level 1 requirements guided its planetary defense investigations. Here, we summarize DART's achievement of those requirements. On 2022 September 26, the DART spacecraft impacted Dimorphos, the secondary member of the Didymos near-Earth asteroid binary system, demonstrating an autonomously navigated kinetic impact into an asteroid with limited prior knowledge for planetary defense. Months of subsequent Earth-based observations showed that the binary orbital period was changed by –33.24 minutes, with two independent analysis methods each reporting a 1σ uncertainty of 1.4 s. Dynamical models determined that the momentum enhancement factor, β, resulting from DART's kinetic impact test is between 2.4 and 4.9, depending on the mass of Dimorphos, which remains the largest source of uncertainty. Over five dozen telescopes across the globe and in space, along with the Light Italian CubeSat for Imaging of Asteroids, have contributed to DART's investigations. These combined investigations have addressed topics related to the ejecta, dynamics, impact event, and properties of both asteroids in the binary system. A year following DART's successful impact into Dimorphos, the mission has achieved its planetary defense requirements, although work to further understand DART's kinetic impact test and the Didymos system will continue. In particular, ESA's Hera mission is planned to perform extensive measurements in 2027 during its rendezvous with the Didymos–Dimorphos system, building on DART to advance our knowledge and continue the ongoing international collaboration for planetary defense.

“…If both bodies have similar mechanical properties, ejecta binding to the system is a function of the bodies' locations in the system's gravity well. The escape speed for ejecta from the system can be approximated by summing the effects of gravity from both bodies at the surface of the target (Makadia et al 2022). A simple analysis shows that the secondary is the better target when the ratio of secondary to primary radii is greater than the corresponding ratio of masses.…”

Section: Deflecting a Binary Asteroidmentioning

confidence: 99%

After DART: Using the First Full-scale Test of a Kinetic Impactor to Inform a Future Planetary Defense Mission

Statler¹,

Raducan

Barnouin

et al. 2022

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NASA’s Double Asteroid Redirection Test (DART) is the first full-scale test of an asteroid deflection technology. Results from the hypervelocity kinetic impact and Earth-based observations, coupled with LICIACube and the later Hera mission, will result in measurement of the momentum transfer efficiency accurate to ∼10% and characterization of the Didymos binary system. But DART is a single experiment; how could these results be used in a future planetary defense necessity involving a different asteroid? We examine what aspects of Dimorphos’s response to kinetic impact will be constrained by DART results; how these constraints will help refine knowledge of the physical properties of asteroidal materials and predictive power of impact simulations; what information about a potential Earth impactor could be acquired before a deflection effort; and how design of a deflection mission should be informed by this understanding. We generalize the momentum enhancement factor β, showing that a particular direction-specific β will be directly determined by the DART results, and that a related direction-specific β is a figure of merit for a kinetic impact mission. The DART β determination constrains the ejecta momentum vector, which, with hydrodynamic simulations, constrains the physical properties of Dimorphos’s near-surface. In a hypothetical planetary defense exigency, extrapolating these constraints to a newly discovered asteroid will require Earth-based observations and benefit from in situ reconnaissance. We show representative predictions for momentum transfer based on different levels of reconnaissance and discuss strategic targeting to optimize the deflection and reduce the risk of a counterproductive deflection in the wrong direction.