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

The NASA DART (Double Asteroid Redirection Test) spacecraft impacted the secondary body of the binary asteroid (65803) Didymos on 2022 September 26and 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 (root-mean-square) 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. (2023) indicate no change in the thermal inertia of the Didymos system following the DART impact. Finally, orbital temperature simulations indicate that sub-surface 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.<br/

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

VADER: Probing the Dark Side of Dimorphos with LICIACube LUKE

The ASI cubesat LICIACube has been part of the first planetary defense mission DART, having among its scopes to complement the DRACO images to better constrain the Dimorphos shape. LICIACube had two different cameras, LEIA and LUKE, and to accomplish its goal, it exploited the unique possibility of acquiring images of the Dimorphos hemisphere not seen by DART from a vantage point of view, in both time and space. This work is indeed aimed at constraining the tridimensional shape of Dimorphos, starting from both LUKE images of the nonimpacted hemisphere of Dimorphos and the results obtained by DART looking at the impacted hemisphere. To this aim, we developed a semiautomatic Computer Vision algorithm, named VADER, able to identify objects of interest on the basis of physical characteristics, subsequently used as input to retrieve the shape of the ellipse projected in the LUKE images analyzed. Thanks to this shape, we then extracted information about the Dimorphos ellipsoid by applying a series of quantitative geometric considerations. Although the solution space coming from this analysis includes the triaxial ellipsoid found by using DART images, we cannot discard the possibility that Dimorphos has a more elongated shape, more similar to what is expected from previous theories and observations. The result of our work seems therefore to emphasize the unique value of the LICIACube mission and its images, making even clearer the need of having different points of view to accurately define the shape of an asteroid.This work was supported by the Italian Space Agency (ASI) within the LICIACube project (ASI-INAF agreement AC No. 2019-31-HH.0) and by the DART mission, NASA contract 80MSFC20D0004

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

Successful kinetic impact into an asteroid for planetary defence

Documento escrito por un elevado número de autores/as, solo se referencia el/la que aparece en primer lugar y los/as autores/as pertenecientes a la UC3M.Although no known asteroid poses a threat to Earth for at least the next century, the catalogue of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation1,2. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid1,2,3. A test of kinetic impact technology was identified as the highest-priority space mission related to asteroid mitigation1. NASA's Double Asteroid Redirection Test (DART) mission is a full-scale test of kinetic impact technology. The mission's target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by the impact of the DART spacecraft4. Although past missions have utilized impactors to investigate the properties of small bodies5,6, those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft's autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in the orbit of Dimorphos7 demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary.This work was supported by the DART mission, NASA Contract No. 80MSFC20D0004. This work was supported by the Italian Space Agency (ASI) within the LICIACube project (ASI-INAF agreement AC n. 2019-31-HH.0). P.S. and P.P. were supported by the Grant Agency of the Czech Republic, grant 20-04431S. B.J.B. was funded by the NASA DART Participating Scientist Program #20-DARTPSP20-0007. S.C. acknowledges funding from the Crosby Distinguished Postdoctoral Fellowship Program of the Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology. G.S.C. was funded by UK Science and Technology Facilities Council Grant ST/S000615/1. F.F. acknowledges funding from the Swiss National Science Foundation (SNSF) Ambizione grant No. 193346. M.J. and S.D.R. acknowledge support by the Swiss National Science Foundation (project number 200021_207359), and from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 870377 (project NEO-MAPP). T.K. is supported by Academy of Finland project 335595 and by institutional support RVO 67985831 of the Institute of Geology of the Czech Academy of Sciences. P.M. acknowledges funding support from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 870377 (project NEO-MAPP), the CNRS through the MITI interdisciplinary programmes, CNES and ESA. N.M. and C.Q.R. acknowledge funding support from the European Commission's Horizon 2020 research and innovation programme under grant agreement no. 870377 (NEO-MAPP project) and support from the Centre National d’Etudes Spatiales (CNES). J.O. has been funded by grant No. PID2021-125883NB-C22 by the Spanish Ministry of Science and Innovation/State Agency of Research MCIN/AEI/10.13039/501100011033 and by ‘ERDF A way of making Europe’. S.R.S. acknowledges support from the NASA DART Participating Scientist Program, award no. 80NSSC22K0318. J.K.S. acknowledges support from NASA award 80NSSC21K1014. J.M.T.-R. acknowledges financial support from the project PID2021-128062NB-I00 funded by Spanish MCIN/AEI/10.13039/501100011033. P.B. acknowledges funding support from Europlanet/University of Edinburgh and Technical University of Kenya. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration

High-resolution shape models of Phobos and Deimos from stereophotoclinometry

Abstract We created high-resolution shape models of Phobos and Deimos using stereophotoclinometry and united images from Viking Orbiter, Phobos 2, Mars Global Surveyor, Mars Express, and Mars Reconnaissance Orbiter into a single coregistered collection. The best-fit ellipsoid to the Phobos model has radii of (12.95 ± 0.04) km × (11.30 ± 0.04) km × (9.16 ± 0.03) km, with an average radius of (11.08 ± 0.04) km. The best-fit ellipsoid to the Deimos model has radii of (8.04 ± 0.08) km × (5.89 ± 0.06) km × (5.11 ± 0.05) km with an average radius of (6.27 ± 0.07) km. The new shape models offer substantial improvements in resolution over existing shape models, while remaining globally consistent with them. The Phobos model resolves grooves, craters, and other surface features ~ 100 m in size across the entire surface. The Deimos model is the first to resolve geological surface features. These models, associated data products, and a searchable, coregistered collection of images across six spacecraft are publicly available in the Small Body Mapping Tool, and will be archived with the NASA Planetary Data System. These products enable an array of future studies to advance the understanding of Phobos and Deimos, facilitate coregistration of other past and future datasets, and set the stage for planning and operating future missions to the moons, including the upcoming Martian Moons eXploration (MMX) mission. Graphical Abstrac

Toward Prebiotic Chemistry on Titan: Impact Experiments on Organic Haze Particles

Impacts are critical to producing the aqueous environments necessary to stimulate prebiotic chemistry on Titan’s surface. Furthermore, organic hazes resting on the surface are a likely feedstock of biomolecules. In this work, we conduct impact experiments on laboratory-produced organic haze particles and haze/sand mixtures and analyze these samples for life’s building blocks. Samples of unshocked haze and sand particles are also analyzed to determine the change in biomolecule concentrations and distributions from shocking. Across all samples, we detect seven nucleobases, nine proteinogenic amino acids, and five other biomolecules (e.g., urea) using a blank subtraction procedure to eliminate signals due to contamination. We find that shock pressures of 13 GPa variably degrade nucleobases, amino acids, and a few other organics in haze particles and haze/sand mixtures; however, certain individual biomolecules become enriched or are even produced from these events. Xanthine, threonine, and aspartic acid are enriched or produced in impact experiments containing sand, suggesting these minerals may catalyze the production of these biomolecules. On the other hand, thymine and isoleucine/norleucine are enriched or produced in haze samples containing no sand, suggesting catalytic grains are not necessary for all impact shock syntheses. Uracil, glycine, proline, cysteine, and tyrosine are the most unstable to impact-related processing. These experiments suggest that impacts alter biomolecule distributions on Titan’s surface, and that organic hazes co-occurring with fine-grained material on the surface may provide an initial source for further prebiotic chemistry on Titan

What do small bodies tell us about the formation of the Solar System and the conditions in the early solar nebula?

We formulate major scientific questions about the properties of the solar nebula, and about the formation and early evolution of the first planetesimals, that should be addressed in the 2023-2032 decade. We provide recommendations on small Solar System body spacecraft missions that would address these questions most efficiently

Chromium Isotopic Evidence for Mixing of NC and CC Reservoirs in Polymict Ureilites: Implications for Dynamical Models of the Early Solar System

Nucleosynthetic isotope anomalies show that the first few million years of solar system history were characterized by two distinct cosmochemical reservoirs, CC (carbonaceous chondrites and related differentiated meteorites) and NC (the terrestrial planets and all other groups of chondrites and differentiated meteorites), widely interpreted to correspond to the outer and inner solar system, respectively. At some point, however, bulk CC and NC materials became mixed, and several dynamical models offer explanations for how and when this occurred. We use xenoliths of CC materials in polymict ureilite (NC) breccias to test the applicability of such models. Polymict ureilites represent regolith on ureilitic asteroids but contain carbonaceous chondrite-like xenoliths. We present the first 54Cr isotope data for such clasts, which, combined with oxygen and hydrogen isotopes, show that they are unique CC materials that became mixed with NC materials in these breccias. It has been suggested that such xenoliths were implanted into ureilites by outer solar system bodies migrating into the inner solar system during the gaseous disk phase ~3-5 Myr after CAI, as in the "Grand Tack" model. However, combined textural, petrologic, and spectroscopic observations suggest that they were added to ureilitic regolith at ~50-60 Myr after CAI, along with ordinary, enstatite, and Rumuruti-type chondrites, as a result of breakup of multiple parent bodies in the asteroid belt at this time. This is consistent with models for an early instability of the giant planets. The C-type asteroids from which the xenoliths were derived were already present in inner solar system orbits

Shape Modeling of Dimorphos for the Double Asteroid Redirection Test (DART)

International audienceThe Double Asteroid Redirection Test (DART) is the first planetary defense test mission. It will demonstrate the kinetic impactor technique by intentionally colliding the DART spacecraft with the near-Earth asteroid Dimorphos. The main DART spacecraft is accompanied by the Italian Space Agency Light Italian CubeSat for Imaging of Asteroids (LICIACube). Shape modeling efforts will estimate the volume of Dimorphos and constrain the nature of the impact site. The DART mission uses stereophotoclinometry (SPC) as its primary shape modeling technique. DART is essentially a worst-case scenario for any image-based shape modeling approach because images taken by the camera on board the DART spacecraft, called the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO), possess little stereo and no lighting variation; they simply zoom in on the asteroid. LICIACube images add some stereo, but the images are substantially lower in resolution than the DRACO images. Despite the far-from-optimal imaging conditions, our tests indicate that we can identify the impact site to an accuracy and precision better than 10% the size of the spacecraft core, estimate the volume of Dimorphos to better than 25%, and measure tilts at the impact site over the scale of the spacecraft with an accuracy better than 7°. In short, we will know with excellent accuracy where the DART spacecraft hit, with reasonable knowledge of local tilt, and determine the volume well enough that uncertainties in the density of Dimorphos will be comparable to or dominate the uncertainty in the estimated mass. The tests reported here demonstrate that SPC is a robust technique for shape modeling, even with suboptimal images