Double Asteroid Redirection Test Research Articles

Statistical Analysis of Near-surface Structure and Material Properties on Momentum Transfer in Rubble Pile Targets Impacted by Kinetic Impactors

Rubble pile asteroids consist of reassembled fragments of once larger monolithic asteroid parent bodies. Recent spacecraft missions to asteroids like Itokawa, Ryugu, Bennu, and Dimorphos suggest that rubble pile asteroids are common in the asteroid population, and rubble piles could be a likely structure among potentially hazardous objects. Therefore, it is important to understand the response of rubble pile targets to kinetic impacts for potential future deflection needs. The recent Double Asteroid Redirection Test (DART) mission motivates an investigation of kinetic impacts into rubble pile targets to understand their effects on deflection. Here, we simulate kinetic impacts into Dimorphos-sized asteroid targets to understand the effect of the impact site structure on the deflection efficiency of relevant sizes for planetary defense. We perform 52 two-dimensional simulations where we vary the impact site structure of the impact site, the target porosity, and the material behavior/strength model to understand their relative effects on crater size and the momentum enhancement factor (β). We find that the effects of the impact site on both crater size and β are greatest for impacts into weaker targets, where impact sites rich in matrix material result in statistically larger craters and higher βs compared to impact sites rich in boulder material. Further, impact site structures that promote increased boulder ejection result in larger β values. These results provide important intuition to understand the DART impact and to extrapolate results to future potential missions.

Near-infrared Spectral Homogeneity of the Didymos System Before and After the DART Impact* * Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the Istituto Nazionale di Astrofisica (INAF) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias

We spectroscopically characterized the Didymos system, target of the Double Asteroid Redirection Test (DART)/Light Italian Cubesat for Imaging of Asteroids (LICIACube) space mission, close in time to the DART impact event, during six nights between 2022 August and November at Telescopio Nazionale Galileo. Here, we show that near-infrared (NIR) spectra (0.75–2.25 μm) look mostly similar within the same night and between different nights. They are in good agreement with the only spectrum previously available in the literature, observed almost 20 years before those reported in this paper. During one of the observing nights we also obtain spectroscopy information on the ejecta tail induced by the DART impact. The spectrum of the ejecta tail is also very similar to Didymos/Dimorphos itself. All of these aspects seem to suggest that the Didymos system in the NIR looks mostly homogeneous, with very subtle spectral variations.

Macroscale Roughness Reveals the Complex History of Asteroids Didymos and Dimorphos

Morphological mapping is a fundamental step in studying the processes that shaped an asteroid surface. However, it is challenging and often requires multiple independent assessments by trained experts. Here we present fast methods to detect and characterize meaningful terrains from the topographic roughness: entropy of information, and local mean surface orientation. We apply our techniques to Didymos and Dimorphos, the target asteroids of NASA's Double Asteroid Redirection Test mission—the first attempt to deflect an asteroid. Our methods reliably identify morphological units at multiple scales. The comparative study reveals various terrain types, signatures of processes that transformed Didymos and Dimorphos. Didymos shows the most heterogeneity and morphology that indicate recent resurfacing events. Dimorphos is comparatively rougher than Didymos, which may result from the formation process of the binary pair and past interaction between the two bodies. Our methods can be readily applied to other bodies and data sets.

Delivery of DART Impact Ejecta to Mars and Earth: Opportunity for Meteor Observations

NASA’s Double Asteroid Redirection Test (DART) and ESA’s Hera missions offer a unique opportunity to investigate the delivery of impact ejecta to other celestial bodies. We performed ejecta dynamical simulations using 3 million particles categorized into three size populations (10 cm, 0.5 cm, and 30 μm) and constrained by early postimpact LICIACube observations. The main simulation explored ejecta velocities ranging from 1 to 1000 m s−1, while a secondary simulation focused on faster ejecta with velocities from 1 to 2 km s−1. We identified DART ejecta orbits compatible with the delivery of meteor-producing particles to Mars and Earth. Our results indicate the possibility of ejecta reaching the Mars Hill sphere in 13 yr for launch velocities around 450 m s−1, which is within the observed range. Some ejecta particles launched at 770 m s−1 could reach Mars's vicinity in 7 yr. Faster ejecta resulted in a higher flux delivery toward Mars and particles impacting the Earth Hill sphere above 1.5 km s−1. The delivery process is slightly sensitive to the initial observed cone range and driven by synodic periods. The launch locations for material delivery to Mars were predominantly north of the DART impact site, while they displayed a southwestern tendency for the Earth–Moon system. Larger particles exhibit a marginally greater likelihood of reaching Mars, while smaller particles favor delivery to Earth–Moon, although this effect is insignificant. To support observational campaigns for DART-created meteors, we provide comprehensive information on the encounter characteristics (orbital elements and radiants) and quantify the orbital decoherence degree of the released meteoroids.

Impact Momentum Transfer—Insights from Numerical Simulation of Impacts on Large Boulders of Asteroids

Asteroids pose potential hazards to Earth. The recent NASA Double Asteroid Redirection Test mission successfully demonstrated the change of an asteroid’s orbit by a kinetic impactor. This study focuses on impact-induced vertical momentum transfer efficiency (β − 1) considering various impact angles and subsurface boulder arrangements. Utilizing the iSALE-3D shock physics code, we simulate oblique impacts on different subsurface boulder configurations. Our results show that vertical ejecta momentum decreases with obliquity, with buried boulders inducing an anti-armoring effect. We define the direct impact-contacted boulder as the primary boulder and the surrounding boulders as secondary. The anti-armoring effect is most pronounced when the primary boulder is just below the surface, amplifying β – 1 by 50%. Impact angles between 60° and 75° exhibit a critical drop in ejecta momentum. An in-depth exploration of subsurface boulder arrangements reveals that secondary boulders have a minimal effect on vertical momentum transfer efficiency. Varying the size and separation of secondary boulders suggests that these subsurface features can either enhance or diminish the overall β − 1, providing insights into the dynamics of rubble-pile asteroids. In addition, impact melting is explored in our simulations, which suggests a minimal melt retention on Dimorphos’s surface. Volumes of retained melt differ by an order of magnitude for impacts on the homogeneous regolith and on targets with buried boulders. In summary, this study provides insights into the effect of subsurface boulders and impact angles on vertical momentum transfer efficiency, which is crucial for understanding asteroid deflection by a kinetic impactor.

Science Product Pipelines and Archive Architecture for the DART Mission

On 2022 September 26, the Double Asteroid Redirection Test (DART) mission was the first successful demonstration of a kinetic impactor for planetary defense. The DART mission utilized a novel autonomous data processing pipeline architecture to quickly produce and analyze the quality of raw and calibrated images from the camera mounted on board the spacecraft. Optimization of the data processing pipeline allowed the final 150 images prior to impact to be calibrated and delivered to the Investigation Team and the press within 15 minutes of acquisition. A data quality analysis pipeline allowed for rapid identification of detector misconfigurations, missing data, and other adverse events. DART data products, along with data from LICIACube and data from ground observatories, used common file formats to facilitate the development of analysis and archiving software. This architecture is described for future missions with large volumes of data and an emphasis on quick-turnaround applications such as planetary defense.

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.

Mechanical properties of rubble pile asteroids (Dimorphos, Itokawa, Ryugu, and Bennu) through surface boulder morphological analysis

Planetary defense efforts rely on estimates of the mechanical properties of asteroids, which are difficult to constrain accurately from Earth. The mechanical properties of asteroid material are also important in the interpretation of the Double Asteroid Redirection Test (DART) impact. Here we perform a detailed morphological analysis of the surface boulders on Dimorphos using images, the primary data set available from the DART mission. We estimate the bulk angle of internal friction of the boulders to be 32.7 ± 2. 5° from our measurements of the roundness of the 34 best-resolved boulders ranging in size from 1.67–6.64 m. The elongated nature of the boulders around the DART impact site implies that they were likely formed through impact processing. Finally, we find striking similarities in the morphology of the boulders on Dimorphos with those on other rubble pile asteroids (Itokawa, Ryugu and Bennu). This leads to very similar internal friction angles across the four bodies and suggests that a common formation mechanism has shaped the boulders. Our results provide key inputs for understanding the DART impact and for improving our knowledge about the physical properties, the formation and the evolution of both near-Earth rubble-pile and binary asteroids.

Fast boulder fracturing by thermal fatigue detected on stony asteroids

Spacecraft observations revealed that rocks on carbonaceous asteroids, which constitute the most numerous class by composition, can develop millimeter-to-meter-scale fractures due to thermal stresses. However, signatures of this process on the second-most populous group of asteroids, the S-complex, have been poorly constrained. Here, we report observations of boulders’ fractures on Dimorphos, which is the moonlet of the S-complex asteroid (65803) Didymos, the target of NASA’s Double Asteroid Redirection Test (DART) planetary defense mission. We show that the size-frequency distribution and orientation of the mapped fractures are consistent with formation through thermal fatigue. The fractures’ preferential orientation supports that these have originated in situ on Dimorphos boulders and not on Didymos boulders later transferred to Dimorphos. Based on our model of the fracture propagation, we propose that thermal fatigue on rocks exposed on the surface of S-type asteroids can form shallow, horizontally propagating fractures in much shorter timescales (100 kyr) than in the direction normal to the boulder surface (order of Myrs). The presence of boulder fields affected by thermal fracturing on near-Earth asteroid surfaces may contribute to an enhancement in the ejected mass and momentum from kinetic impactors when deflecting asteroids.

The geology and evolution of the Near-Earth binary asteroid system (65803) Didymos

Images collected during NASA’s Double Asteroid Redirection Test (DART) mission provide the first resolved views of the Didymos binary asteroid system. These images reveal that the primary asteroid, Didymos, is flattened and has plausible undulations along its equatorial perimeter. At high elevations, its surface is rough and contains large boulders and craters; at low elevations its surface is smooth and possesses fewer large boulders and craters. Didymos’ moon, Dimorphos, possesses an intimate mixture of boulders, several asteroid-wide lineaments, and a handful of craters. The surfaces of both asteroids include boulders that are large relative to their host body, suggesting that both asteroids are rubble piles. Based on these observations, our models indicate that Didymos has a surface cohesion ≤ 1 Pa and an interior cohesion of ∼10 Pa, while Dimorphos has a surface cohesion of <0.9 Pa. Crater size-frequency analyzes indicate the surface age of Didymos is 40–130 times older than Dimorphos, with likely absolute ages of ~\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document}12.5 Myr and <0.3 Myr, respectively. Solar radiation could have increased Didymos’ spin rate leading to internal deformation and surface mass shedding, which likely created Dimorphos.

Impact-induced deformation away from the impact point on small asteroids

Abstract We investigated the propagation of energy and momentum inside a small gravitational aggregate asteroid following a hyper-velocity impact, comparable to NASA’s Double Asteroid Redirection Test on asteroid Dimorphos. We show that the impact energy damps rapidly inside different kinds of granular structures, unable to reach the antipodal hemisphere of the impact. However, global reshaping of the asteroid after the formation of a sizeable (&amp;gt;1/3 of target size) crater causes meter-range displacement of boulders on the antipodal hemisphere due to mass rearrangement to achieve a new equilibrium shape. As a result, a surface depression opposite to the crater is formed, which may produce some surface refreshment. The boulder mass ejection following the synthetic DART-like impact is estimated to be at least $0.1\, {{\%}}$ of the mass of the Dimorphos-like target, in agreement with recent detections of boulders ejected from the actual 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.

Rotational lightcurves of Dimorphos and constraints on its post-DART impact spin state

Dimorphos, the secondary member of the binary asteroid (65803) Didymos, was impacted by NASA’s Double Asteroid Redirection Test (DART) spacecraft on September 26, 2022. Images taken with the DART’s DRACO camera before the impact showed that Dimorphos’s original shape was nearly rotationally symmetric, close to an oblate spheroid, and it was probably in a synchronous spin state. As such, it did not show a detectable secondary brightness variation before the DART impact in the integral light from the binary system. However, numerical impact models predicted that the DART impact could change both its shape and spin state, signatures of which could be detected with high-quality lightcurve observations. We have analyzed the best photometric observations of the Didymos–Dimorphos system that were taken during its favorable observing and geometric conditions in December 2022 and January 2023 and detected a significant secondary rotational lightcurve with amplitudes (in the total light from the primary and secondary) ranging from 0.008 to 0.031 mag at 7 distinct epochs. We estimate that the apparent cross section of Dimorphos varied with a relative amplitude (normalized to the mean cross section) between ±0.07 and ±0.24 over its rotation on the individual epochs. The observed changes of Dimorphos’s apparent cross-section amplitude over its rotation suggest an attitude instability, showing variations of Dimorphos’s obliquity. The lightcurve minima are approximately aligned, to within 30∘in mean anomaly, with the mutual events between the components of the binary system. The observations suggest that Dimorphos is in an excited, non-principal axis (NPA) spin state where, on average, it is tidally locked. By comparing the observations to high-fidelity simulations, we find that a moderate amount of NPA rotation in Dimorphos after the DART impact is required to reproduce the observed lightcurves. This NPA rotation is limited to around on-average synchronous or anti-synchronous configurations of Dimorphos. We also find Dimorphos elongations with the equatorial axis ratios a/b between 1.1 and 1.4 are generally consistent with the observed mean apsidal precession rate. We predict that when the ESA’s Hera spacecraft arrives to the Didymos–Dimorphos system in late 2026, it will still find Dimorphos in the NPA spin state, which places additional constraints on the operations of the spacecraft to achieve its objectives.

Recent collisional history of (65803) Didymos

The Double Asteroid Redirection Test (DART, NASA) spacecraft revealed that the primary of the (65803) Didymos near-Earth asteroid (NEA) binary system is not exactly the expected spinning top shape observed for other km-size asteroids. Ground based radar observations predicted that such shape was compatible with the uncertainty along the direction of the asteroid spin axis. Indeed, Didymos shows crater and landslide features, and evidence for boulder motion at low equatorial latitudes. Altogether, the primary seems to have undergone sudden structural failure in its recent history, which may even result in the formation of the secondary. The high eccentricity of Didymos sets its aphelion distance inside the inner main belt, where it spends more than 1/3 of its orbital period and it may undergo many more collisions than in the NEA region. In this work, we investigate the collisional environment of this asteroid and estimate the probability of collision with multi-size potential impactors. We analyze the possibility that such impacts produced the surface features observed on Didymos by comparing collisional intervals with estimated times for surface destabilization by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect. We find that collisional effects dominate over potential local or global deformation due to YORP spin up.

Long-term Monitoring of Didymos with the LCOGT Network and MRO after the DART Impact

The world’s first planetary defense test mission was carried out in late 2022 by NASA’s Double Asteroid Redirection Test (DART) mission. The main DART spacecraft, which was accompanied by the ASI-provided LICIACube cubesat, intentionally impacted Dimorphos, the smaller secondary of the near-Earth object binary system (65803) Didymos, on 2022 September 26. The impact released a large amount of ejecta, which, combined with the spacecraft’s momentum, produced the observed 33 ± 1 minute period change that was subsequently observed from ground-based telescopes. The DART mission, in addition to having successfully changed the orbital period of Dimorphos, also activated the asteroid as a result of the impact but under known conditions, unlike other impacts on asteroids. We have conducted long-term monitoring over 5 months following the impact with the Las Cumbres Observatory Global Telescope (LCOGT) network and Magdalena Ridge Observatory (MRO). This was supplemented by almost 3 months of more sparsely sampled data, primarily from educational users of the LCOGT network during the period from 2022 July 5 to 2022 September 25, prior to the impact date of 2022 September 26. Here we report the observations of the Didymos system and DART impact ejecta with the telescopes of the LCOGT network from T+1.93 days to T+151.3 days after impact, and we study the evolving morphology of the ejecta cloud and evolving tail over the entire length of the data set. In addition, we combined these intensive data sets with the earlier sparse observations over the ∼90 days prior to impact to derive a new disk-integrated phase function model using the H, G 1, G 2 parameterization.

DART Impact Ejecta Plume Evolution: Implications for Dimorphos

The NASA Double Asteroid Redirection Test (DART) spacecraft impacted the moon Dimorphos of the [65803] Didymos binary system and changed the binary orbit period, demonstrating asteroid deflection by a kinetic impact and indicating that more momentum was transferred to Dimorphos by escaping impact ejecta than was incident with DART. Images of the DART impact ejecta plume were obtained by the Light Italian cubesat for Imaging of Asteroids (LICIACube) in the first few minutes after the DART impact. The ejecta plume imaged by LICIACube 158 s after the DART impact prior to closest approach shows no evidence for plume clearing at low altitude. The ejecta plume imaged 175 s after the DART impact is optically thick up to projected altitudes of 200 m above the surface of Dimorphos. These observations are compared with models of the impact ejecta plume optical depth, structure, and evolution, which are developed from point-source scaling models fitted to numerical simulations of the DART impact into a rubble pile Dimorphos with different material strengths. The observations of the impact plume optical depth and the high momentum transfer from the DART impact are not consistent with impact and ejecta plume models assuming the Dimorphos cohesive strength to be as high as 5000 Pa. Models with 5 and 50 Pa Dimorphos cohesive strength provide the overall best consistency with plume opacity observations and high momentum transfer.

DART: Latest results from the Dimorphos impact and a look forward to future planetary defense initiatives

DART, the Double Asteroid Redirection Test, successfully impacted asteroid Dimorphos on September 26, 2022, becoming the first mission to demonstrate asteroid deflection. Shared live via a NASA broadcast, over a million concurrent viewers around the world watched as the DART spacecraft streamed images to Earth up to the final second before its impact with Dimorphos. In this paper, we share the final phases of the DART encounter and the latest results from the DART Investigation Team's analysis of ground and space-based data. This includes measurements on the amount of deflection that DART imparted on Dimorphos, a determination of the momentum transfer enhancement factor, and results on understanding the geology and surface characteristics of the impact site. The success of the DART mission paves the future for a bold international Planetary Defense program. We also share ideas on bolstering international coordination, developing new technologies that can mitigate different types of asteroid threats, and closing identified gaps in our overall preparedness.

The Unusual Brightness Phase Curve of (65803) Didymos

On 2022 September 26, NASA's Double Asteroid Redirection Test (DART) successfully hit Dimorphos, the smaller companion of the binary system formed with the asteroid (65803) Didymos. Both the binary system and the impact event were imaged by the Light Italian Cubesat for Imaging of Asteroids, detached from DART 15 days before the impact. Images from the onboard LUKE red, green, and blue camera together with ground-based observations enabled the reconstruction of Didymos's brightness phase curve, with phase angles ranging from 2.35° to 107.7°. The opposition effect regime was studied using the exponential-linear equation, the “Shevchenko” function and the linear-by-parts model while the IAU-official HG1G2 magnitude system was applied to the full phase curve. The opposition effect indicates an unusual asteroid surface for an S type, with characteristics similar to M-type asteroids. While the HG1G2 parameters from the full phase curve place Didymos well among asteroids of the taxonomic C complex. Didymos’s phase curve parameters when compared to near-Earth asteroids are very close to the Q type (1862) Apollo, indicating possible depletion of fine submicrometric grains through resurfacing. Didymos's geometric albedo (0.15 ± 0.01) is reported to be 30%–45% smaller than the average geometric albedo for near-Earth S types (0.26 ± 0.04). We propose that Didymos might be an LL ordinary chondrite analog containing albedo-suppressing, shock-darkened/impact melt minerals that have undergone resurfacing processes in the past. A comparison with meteorites indicates that, less likely, Didymos could also contain materials analog to carbon-bearing brecciated L3 ordinary chondrites.

Orbital and Physical Characterization of Asteroid Dimorphos Following the DART Impact

The Double Asteroid Redirection Test (DART) mission impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos, on 2022 September 26 UTC. We estimate the changes in the orbital and physical properties of the system due to the impact using ground-based photometric and radar observations, as well as DART camera observations. Under the assumption that Didymos is an oblate spheroid, we estimate that its equatorial and polar radii are 394 ± 11 m and 290 ± 16 m, respectively. We estimate that the DART impact instantaneously changed the along-track velocity of Dimorphos by −2.63 ± 0.06 mm s−1. Initially, after the impact, Dimorphos’s orbital period had changed by −32.7 minutes ± 16 s to 11.377 ± 0.004 hr. We find that over the subsequent several weeks the orbital period changed by an additional 34 ± 15 s, eventually stabilizing at 11.3674 ± 0.0004 hr. The total change in the orbital period was −33.25 minutes ±1.5 s. The postimpact orbit exhibits an apsidal precession rate of 6.7 ± 0.°2 day−1. Under our model, this rate is driven by the oblateness parameter of Didymos, J 2, as well as the spherical harmonics coefficients, C 20 and C 22, of Dimorphos’s gravity. Under the assumption that Dimorphos is a triaxial ellipsoid with a uniform density, its C 20 and C 22 estimates imply axial ratios, a/b and a/c, of about 1.3 and 1.6, respectively. Preimpact images from DART indicate Dimorphos’s shape was close to that of an oblate spheroid, and thus our results indicate that the DART impact significantly altered the shape of Dimorphos.

Pre-impact Thermophysical Properties and the Yarkovsky Effect of NASA DART Target (65803) Didymos

The NASA Double Asteroid Redirection Test (DART) spacecraft impacted the secondary body of the binary asteroid (65803) Didymos on 2022 September 26 and altered its orbit about the primary body. Before the DART impact, we performed visible and mid-infrared observations to constrain the pre-impact thermophysical properties of the Didymos system and to model its Yarkovsky effect. Analysis of the photometric phase curve derives a Bond albedo of 0.07 ± 0.01, and a thermophysical analysis of the mid-infrared observations derives a thermal inertia of 320 ± 70 J m−2 K−1 s−1/2 and a thermal roughness of 40° ± 3° rms slope. These properties are compatible with the ranges derived for other S-type near-Earth asteroids. Model-to-measurement comparisons of the Yarkovsky orbital drift for Didymos derives a bulk density of 2750 ± 350 kg m−3, which agrees with other independent measures based on the binary mutual orbit. This bulk density indicates that Didymos is spinning at or near its critical spin-limit at which self-gravity balances equatorial centrifugal forces. Furthermore, comparisons with the post-impact infrared observations presented in Rivkin et al. indicate no change in the thermal inertia of the Didymos system following the DART impact. Finally, orbital temperature simulations indicate that subsurface water ice is stable over geologic timescales in the polar regions if present. These findings will be investigated in more detail by the upcoming ESA Hera mission.