Dynamical Evolution of the Didymos-Dimorphos Binary Asteroid as Rubble Piles following the DART Impact

Previous efforts have modeled the Didymos system as two irregularly shaped rigid bodies, although it is likely that one or both components are in fact rubble piles. Here, we relax the rigid-body assumption to quantify how this affects the spin and orbital dynamics of the system following the DART impact. Given known fundamental differences between our simulation codes, we find that faster rigid-body simulations produce nearly the same result as rubble-pile models in scenarios with a moderate value for the momentum enhancement factor, $\beta$ ($\beta{\sim}3$) and an ellipsoidal secondary. This indicates that the rigid-body approach is likely adequate for propagating the post-impact dynamics necessary to meet DART Mission requirements. Although, if Dimorphos has a highly-irregular shape or structure, or if $\beta$ is unexpectedly large, then rubble-pile effects may become important. If Dimorphos's orbit and spin state are sufficiently excited, then surface particle motion is also possible. However, these simulations are limited in their resolution and range of material parameters, so they serve as a demonstration of principle, and Future work is required to fully understand the likelihood and magnitude of surface motion.Comment: 21 pages, 19 figures, published in PS

Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos

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, β=3.61+0.19−0.25(1σ). 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

Libration-induced Orbit Period Variations Following the DART Impact

The Double Asteroid Redirection Test (DART) mission will be the first test of a kinetic impactor as a means of planetary defense. In late 2022, DART will collide with Dimorphos, the secondary in the Didymos binary asteroid system. The impact will cause a momentum transfer from the spacecraft to the binary asteroid, changing the orbit period of Dimorphos and forcing it to librate in its orbit. Owing to the coupled dynamics in binary asteroid systems, the orbit and libration state of Dimorphos are intertwined. Thus, as the secondary librates, it also experiences fluctuations in its orbit period. These variations in the orbit period are dependent on the magnitude of the impact perturbation, as well as the system’s state at impact and the moments of inertia of the secondary. In general, any binary asteroid system whose secondary is librating will have a nonconstant orbit period on account of the secondary’s fluctuating spin rate. The orbit period variations are typically driven by two modes: a long period and a short period, each with significant amplitudes on the order of tens of seconds to several minutes. The fluctuating orbit period offers both a challenge and an opportunity in the context of the DART mission. Orbit period oscillations will make determining the post-impact orbit period more difficult but can also provide information about the system’s libration state and the DART impact

Dimorphos's Orbit Period Change and Attitude Perturbation due to Its Reshaping after the DART Impact

On 2022 September 26 (UTC), NASA's Double Asteroid Redirection Test (DART) mission achieved a successful impact on Dimorphos, the secondary component of the near-Earth binary asteroid system (65803) Didymos. Subsequent ground-based observations suggest a significant reshaping of Dimorphos, with its equatorial axis ratio changing from 1.06 to ∼1.3. Here we report the effects of this reshaping event on Dimorphos's orbit and attitude. Given the reported reshaping magnitude, our mutual dynamics simulations show that approximately 125 s of the observed 33 minute orbit period change after the DART impact may have resulted from reshaping. This value, however, is sensitive to the precise values of Dimorphos's post-impact axis ratios and may vary by up to 2 times that amount, reaching approximately 250 s within the current uncertainty range. While the rotational state of the body is stable at the currently estimated axis ratios, even minor changes in these ratios or the introduction of shape asymmetry can render its attitude unstable. The perturbation to Dimorphos's orbital and rotational state delivered by the impact directly, combined with any reshaping, leads to a strong possibility for a tumbling rotation state. To accurately determine the momentum enhancement factor (β) through measurements by the European Space Agency's Hera spacecraft and to evaluate the effectiveness of the kinetic deflection technique for future planetary defense initiatives, the effects of reshaping should not be overlooked.This work was supported in part by the DART mission, NASA contract 80MSFC20D0004 to JHU/APL. R.N. acknowledges support from NASA/FINESST (NNH20ZDA001N). S.D.R. and M.J. acknowledge support from the Swiss National Science Foundation (project number 200021_207359). P.M. acknowledges funding support from the French Space Agency CNES and The University of Tokyo. P.P. acknowledges support from the grant Agency of the Czech Republic, grant 23-04946S. S.R.S. acknowledges support from the DART Participating Scientist Program, grant No. 80NSSC22K0318. A.C.B. and P.Y.L. acknowledge funding by the NEO-MAPP project 717 GA 870377, EC H2020-SPACE-718 2018-2020/H2020-SPACE-2019, and by MICINN (Spain) PGC2021, PID2021-125883NB-C21. P.Y.L. acknowledges funding from the European Space Agency OSIP contract N.4000136043/21/NL/GLC/my. A portion of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (No. 80NM0018D0004)

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

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

The Dynamical State of the Didymos System before and after the DART Impact

NASA's Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the natural satellite of (65803) Didymos, on 2022 September 26, as a first successful test of kinetic impactor technology for deflecting a potentially hazardous object in space. The experiment resulted in a small change to the dynamical state of the Didymos system consistent with expectations and Level 1 mission requirements. In the preencounter paper, predictions were put forward regarding the pre- and postimpact dynamical state of the Didymos system. Here we assess these predictions, update preliminary findings published after the impact, report on new findings related to dynamics, and provide implications for ESA's Hera mission to Didymos, scheduled for launch in 2024 October with arrival in 2026 December. Preencounter predictions tested to date are largely in line with observations, despite the unexpected, flattened appearance of Didymos compared to the radar model and the apparent preimpact oblate shape of Dimorphos (with implications for the origin of the system that remain under investigation). New findings include that Dimorphos likely became prolate due to the impact and may have entered a tumbling rotation state. A possible detection of a postimpact transient secular decrease in the binary orbital period suggests possible dynamical coupling with persistent ejecta. Timescales for damping of any tumbling and clearing of any debris are uncertain. The largest uncertainty in the momentum transfer enhancement factor of the DART impact remains the mass of Dimorphos, which will be resolved by the Hera mission

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

After DART: Using the First Full-scale Test of a Kinetic Impactor to Inform a Future Planetary Defense Mission Thomas S. Statler 1 , Sabina D. Raducan 2 , Olivier S. Barnouin 3 , Mallory E. DeCoster 3 , Steven R. Chesley 4 , Brent Barbee 5 , Harrison F. Agrusa 6 , Saverio Cambioni 7 , Andrew F. Cheng 3 , Elisabetta Dotto 8 , Siegfried Eggl9 , Eugene G. Fahnestock 4 , Fabio Ferrari 2 , Dawn Graninger 3 , Alain Herique 10 , Isabel Herreros 11 , Masatoshi Hirabayashi 12,13 , Stavro Ivanovski 14 , Martin Jutzi 2 , Özgür Karatekin 15 , Alice Lucchetti 16 , Robert Luther 17 , Rahil Makadia 9 , Francesco Marzari 18 , Patrick Michel 19 , Naomi Murdoch 20 , Ryota Nakano13 , Jens Ormö 11 , Maurizio Pajola 16 , Andrew S. Rivkin3 , Alessandro Rossi 21 , Paul Sánchez 22 , Stephen R. Schwartz 23 , Stefania Soldini 24 , Damya Souami 19 , Angela Stickle 3 , Paolo Tortora 25 , Josep M. Trigo-Rodríguez 26,27 , Flaviane Venditti 28 , Jean-Baptiste Vincent 29 , and Kai Wünnemann 17,30 1 Planetary Defense Coordination Office and Planetary Science Division, NASA Headquarters, 300 Hidden Figures Way SW, Washington, DC 20546, USA [email protected] 2 Space Research and Planetary Sciences, Physics Institute, University of Bern, Bern, 3012, Switzerland 3 Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA 4 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA 5 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 6 Department of Astronomy, University of Maryland, College Park, MD 20742, USA 7 Department of Earth, Atmospheric & Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA 8 INAF-Osservatorio Astronomico di Roma, Rome, I-00078, Italy 9 Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA 10 Univ. Grenoble Alpes, CNRS, CNES, IPAG, F-38000 Grenoble, France 11 Centro de Astrobiología CSIC-INTA, Instituto Nacional de Técnica Aeroespacial, E-28850 Torrejón de Ardoz, Spain 12 Department of Geosciences, Auburn University, Auburn, AL 36849, USA 13 Department of Aerospace Engineering, Auburn University, Auburn, AL 36849, USA 14 INAF- Osservatorio Astronomico di Trieste, Trieste I-34143, Italy 15 Royal Observatory of Belgium, Belgium 16 INAF-Astronomical Observatory of Padova, Padova I-35122, Italy 17 Museum für Naturkunde—Leibniz Institute for Evolution and Biodiversity Science, Germany 18 University of Padova, Padova, Italy 19 Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice F-06304, France 20 Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France 21 IFAC-CNR, Sesto Fiorentino I-50019, Italy 22 Colorado Center for Astrodynamics Research, University of Colorado Boulder, Boulder, CO 80303, USA 23 Planetary Science Institute, Tucson, AZ 85719, USA 24 Department of Mechanical, Materials and Aerospace Engineering, University of Liverpool, Liverpool, UK 25 Alma Mater Studiorum—Università di Bologna, Department of Industrial Engineering, Interdepartmental Center for Industrial Research in Aerospace, Via Fontanelle 40—Forlì (FC)—I-47121, Italy 26 Institute of Space Sciences (ICE, CSIC), Cerdanyola del Vallès, E-08193 Barcelona, Catalonia, Spain 27 Institut d’Estudis Espacials de Catalunya (IEEC), Ed. Nexus, E-08034 Barcelona, Catalonia, Spain 28 Arecibo Observatory, University of Central Florida, HC-3 Box 53995, Arecibo, PR 00612, USA 29 German Aerospace Center, DLR Berlin, Germany 30 Freie Universität Berlin, Germany Received 2022 August 9; revised 2022 September 18; accepted 2022 September 22; published 2022 October 28 Abstract 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

After DART: Using the first full-scale test of a kinetic impactor to inform a future planetary defense mission

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 $\beta$, showing that a particular direction-specific $\beta$ will be directly determined by the DART results, and that a related direction-specific $\beta$ is a figure of merit for a kinetic impact mission. The DART $\beta$ 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

Achievement of the planetary defense investigations of the Double Asteroid Redirection Test (DART) mission

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

Dimorphos Orbit Determination from Mutual Events Photometry

The NASA Double Asteroid Redirection Test spacecraft successfully impacted the Didymos–Dimorphos binary asteroid system on 2022 September 26 UTC. We provide an update to its preimpact mutual orbit and estimate the postimpact physical and orbital parameters, derived using ground-based photometric observations taken from 2022 July to 2023 February. We found that the total change of the orbital period was −33.240 ± 0.072 minutes (all uncertainties are 3 σ ). We obtained the eccentricity of the postimpact orbit to be 0.028 ± 0.016 and the apsidal precession rate was 7.3 ± 2.0 degrees day ^−1 from the impact to 2022 December 2. The data taken later in 2022 December to 2023 February suggest that the eccentricity dropped close to zero or the orbit became chaotic approximately 70 days after the impact. Most of the period change took place immediately after the impact, but in the few weeks following the impact it was followed by an additional change of $-{27}_{-58}^{+19}$ s or −19 ± 18 s (the two values depend on the approach we used to describe the evolution of the orbital period after the impact—an exponentially decreasing angular acceleration or the assumption of a constant orbital period, which changed abruptly some time after the impact, respectively). We estimate the preimpact Dimorphos–Didymos size ratio was 0.223 ± 0.012 and the postimpact is 0.202 ± 0.018, which indicate a marginally significant reduction of Dimorphos’ volume by (9 ± 9)% as the result of the impact