Anticipated Geological Assessment of the (65803) Didymos–Dimorphos System, Target of the DART–LICIACube Mission

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The Didymos binary asteroid was the target of the Double Asteroid Redirection Test (DART) mission, which intentionally impacted Dimorphos, the smaller member of the binary system. We used the Near-Infrared Spectrograph and Mid-Infrared Instrument instruments on JWST to measure the 0.6–5 and 5–20 μm spectra of Didymos approximately two months after the DART impact. These observations confirm that Didymos belongs to the S asteroid class and is most consistent with LL chondrite composition, as was previously determined from its 0.6–2.5 μm reflectance spectrum. Measurements at wavelengths >2.5 μm show Didymos to have thermal properties typical for an S-complex asteroid of its size and to be lacking absorptions deeper than ∼2% due to OH or H2O. Didymos’ mid-infrared emissivity spectrum is within the range of what has been measured on S-complex asteroids observed with the Spitzer Space Telescope and is most consistent with emission from small (<25 μm) surface particles. We conclude that the observed reflectance and physical properties make the Didymos system a good proxy for the type of ordinary chondrite asteroids that cross near-Earth space, and a good representative of likely future impactors.

Section: Introductionsupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Near to Mid-infrared Spectroscopy of (65803) Didymos as Observed by JWST: Characterization Observations Supporting the Double Asteroid Redirection Test

Rivkin,

Thomas,

Wong

et al. 2023

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“…The DART impact is set to occur at an impact angle that depends on both the spacecraft's incoming trajectory and on the local slope of the target at the impact point (Pajola et al 2022). DART will approach Dimorphos at an angle of ∼10°f rom the orbital plane, but little is currently known about the local topography at the impact site.…”

Section: Effects Of Impact Angle and Local Topography On Deflection P...mentioning

confidence: 99%

Effects of Impact and Target Parameters on the Results of a Kinetic Impactor: Predictions for the Double Asteroid Redirection Test (DART) Mission

Stickle¹,

DeCoster²,

Burger³

et al. 2022

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The Double Asteroid Redirection Test (DART) spacecraft will impact into the asteroid Dimorphos on 2022 September 26 as a test of the kinetic impactor technique for planetary defense. The efficiency of the deflection following a kinetic impactor can be represented using the momentum enhancement factor, β, which is dependent on factors such as impact geometry and the specific target material properties. Currently, very little is known about Dimorphos and its material properties, which introduces uncertainty in the results of the deflection efficiency observables, including crater formation, ejecta distribution, and β. The DART Impact Modeling Working Group (IWG) is responsible for using impact simulations to better understand the results of the DART impact. Pre-impact simulation studies also provide considerable insight into how different properties and impact scenarios affect momentum enhancement following a kinetic impact. This insight provides a basis for predicting the effects of the DART impact and the first understanding of how to interpret results following the encounter. Following the DART impact, the knowledge gained from these studies will inform the initial simulations that will recreate the impact conditions, including providing estimates for potential material properties of Dimorphos and β resulting from DART’s impact. This paper summarizes, at a high level, what has been learned from the IWG simulations and experiments in preparation for the DART impact. While unknown, estimates for reasonable potential material properties of Dimorphos provide predictions for β of 1–5, depending on end-member cases in the strength regime.

“…Images of the newly forming crater, if visible through the plume, will provide additional constraints on the nearsurface porosity and help to constrain the other ejecta response parameters. The full LICIACube data set should provide information on surface properties of Dimorphos, such as geological features, color differences and variegation, boulder distribution, and mass movements, if present (Pajola et al 2022;Poggiali et al 2022), as well as information on the ejecta plume structure and dust dynamics evolution shortly after the DART impact, up to the distance of the LICIACube closest approach (Ivanovski et al 2022;Rossi et al 2022).…”

Section: Additional Constraints From Liciacube and Heramentioning

confidence: 99%

“…(iii) Earth-based observations plus rendezvous mission: A rendezvous mission with radio-science and imaging capabilities would essentially guarantee accurate determinations of mass, volume, and shape, and along with them, bulk density and porosity. In addition, complete mapping of surface features (Pajola et al 2022) and a precise determination of the rotation state would likely be achievable. By tying evidence for surface mass movements to surface slopes, geotechnical stability analyses could constrain the surface cohesion along with analyses of observed ejecta (Perry et al 2022).…”

Section: Target Characterizationmentioning

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.