Context. Robust impact monitoring of near-Earth objects is an essential task of planetary defense. Current systems such as NASA's Sentry-II, NEODyS's CLOMON2, and ESA's Aegis have been highly successful, but independent approaches are essential to ensure reliability and to cross-validate predictions of possible impacts, probabilities, and paths on Earth. Aims. We present NEOForCE (Near-Earth Objects' Forecast of Collisional Events), a new independent monitoring system for asteroid impact prediction. By relying on orbital solutions from DynAstVO at Paris Observatory and using an original methodology for uncertainty propagation, NEOForCE provides an alternative line of verification for future impact assessments and strengthens the overall robustness of planetary defense. Methods. As other monitoring systems do, NEOForCE samples several thousand so-called "virtual asteroids" from the uncertainty region and integrates their orbits up to 100 years into the future. Instead of searching for close approaches of the virtual asteroids themselves with the Earth, our system looks for times when the Earth comes close to the "realistic" uncertainty regions around them, which are mostly stretched along the osculating ellipses of virtual asteroids. For every virtual asteroid and every possible collision time, we also estimate the maximal impact probability, and only if this value is large enough (>5 & times; 10(-8)) do we continue to the next step. In this second step, we compute how the original asteroid orbit should be slightly modified so that the new trajectory leads to an Earth impact, which allows us to confirm the possible collision and estimate the impact probability. Results. We tested NEOForCE against NASA's Sentry-II system on five representative asteroids with a high impact probability and significant number of possible collisions: 2000 SG344, 2005 QK76, 2008 JL3, 2023 DO, and 2008 EX5. NEOForCE successfully recovered almost all of the possible collisions reported by Sentry-II with impact probabilities above 10(-7), demonstrating the robustness of our approach. In addition, NEOForCE identified several potential impacts at the 10(-7)-10(-6) level that Sentry-II did not report.

IntroductionPlanetary surfaces not protected by dense atmospheres suffered by many impacts by asteroids and comets, leaving craters as a reminders of it. Among all craters observed on surfaces of Earth, Mars, Moon, and Venus, about 3-4% are binary craters. It is believed they formed by the simultaneous impacts of the two components of binary asteroid systems.Binary asteroids represent 15% of near-Earth asteroids, apparently at odd with the rate of binary craters on planetary surfaces. Miljkovic et al. showed with 3-D hydrocode simulations that only a fraction of impacts by binary asteroids create distinguishable binary craters, solving the apparent discrepancy with the fraction of binary craters of 3-4%. However, the few binary crater examples in have striking properties: nearly similar size and North-South orientation, unexpected from a population of binary asteroids displaying a typical size ratio of 0.3 and with a mutual orbit closely aligned with the ecliptic.Survey and simulationsA large fraction of impact craters on Mars exhibits thick and continuous ejecta blanket emplaced in a pyroclastic flow-like regime due to the presence of volatile material at the moment of the impact. This facilitates the recognition of synchronous impact events, making the surface of Mars an ideal case to survey for the existence of binary craters and infer the binary asteroids properties.Our study focuses on craters more than 4km in diameter located between latitudes 50°N and 50°S compiled in the database and recently revised by A. Lagain in 2021. We chose this minimum diameter to remove potential bias that could be caused by isolated secondary impacts and this range of latitude to avoid high-latitudes resurfacing processes. Binary craters are recognized based on the morphology of their cavity or their ejecta blanket.The presence of a septum (i.e. a linear contact perpendicular to the direction of both crater centers on their shared rim or ejecta blanket), is one of the main morphological characteristics allowing to identify them, as illustrated on Fig.1. We classify candidates binary craters following Miljkovic scheme: Elliptical, Peanut, Doublet, Tear drop, Overlapping and Circular. We will not analyze the last category as it represents craters whose a binary asteroid impact origin is more uncertain. In parallel, we conduct three-body dynamical simulations to predict the orientation or binary craters on Mars surface as inferred from the known population of binary asteroids, extending the previous work by Melosh and Stansberry.Results and ConclusionsOut of the 31,778 craters we inspected, we identify 28 doublet, 44 peanut, 17 overlapping, 23 tear, and 13 elliptical craters. Using crater scaling laws adapted for Mars impact condition, the size of impactors having formed those craters range between approximately 100 m and 5 km. 28 doublet craters indicate on largely separated binary asteroids with more than 10 diameters of the primary asteroid size.The observed distribution of orientation angle θ of doublet craters as well as the simulated one are presented in Fig.2. It is clearly seen that the distributions are different. We also performed a Kolmogorov-Smirnov test on the two distributions and we can reject with a 99.99% confidence that the two distributions are similar.Our numerical simulations show that neither the separation nor the orientation of the binary asteroid components is affected by tidal forces of Mars. It means that there is an unobserved population of widely separated binaries, whose mutual orbits is not coplanar with their heliocentric orbits. These binary systems are very difficult to be detected by typical lightcurve programs but our results reveal the existence of these systems.

ABSTRACTPlanetary surfaces present binary craters that can be associated with the synchronous impact of binary asteroids. In this work, we identify binary craters on asteroids (1) Ceres and (4) Vesta, and aim to characterize the properties (size ratio and orbital plane) of the binary asteroids that might have formed them. We used global crater databases developed in previous studies and mosaics of images from the NASA DAWN mission. We established selection criteria to identify craters that were most likely a product of the impact of a binary asteroid. We find geomorphological evidence of synchronous impacts on the surfaces of Ceres and Vesta. The associated binary asteroids are widely separated and similar in diameter in contrast to the current census of binary asteroids. The distributions of the orientation of these binary craters on both bodies are statistically different from numerical impact simulations that assume binary asteroids with coplanar mutual and heliocentric orbits. These findings agree with a population of well-separated and similarly sized binary asteroids with non-zero obliquity that remains to be observed.INTRODUCTIONPlanetary surfaces present binary craters that are associated with the synchronous impact of binary asteroids. The detection and characterization of satellites of small asteroids rely on observations by radar echoes for near-Earth asteroids (NEAs) [1] and optical light curves for both NEAs and main belt asteroids (MBAs) [2]. Although these observations are efficient and precise, they are biased by a limited range from the Earth for radar observation and a strong preference for compact and low-obliquity systems for light curves.To have a better understanding of the distribution of the binary asteroid population in the Solar System, we created a catalog of binary craters for Ceres and Vesta that are associated to binary asteroids that might have formed them, focusing on the size ratio and orbital plane of the binary system. Out catalog was based on the global crater databases of Ceres [3] and Vesta [4], combined with high altitude mapping orbit (HAMO) and low altitude mapping orbit (LAMO) images for each body from the NASA’s DAWN mission [5].METHODSAirless planetary objects have their surfaces covered by craters but proximity between two of them is not enough to determine if they are product of the impact of binary asteroids. We created a criterion of classification for binary craters on Ceres and Vesta which main aspects are that:The pairs of craters must be in contact and show a septum. We cannot label objects separated as synchronous because there is no ejecta blanket surrounding them since their surfaces are not hydrated enough. These craters should not exhibit poligonality, which has been observed on Ceres [6], since this feature can be confused with a pair having a septum and be misidentified as synchronous. An inspection on the surroundings is critical to avoid identifying possible secondary craters from previous impacts as a binary asteroid. Each pair of craters must have a similar degradation state, and similar depth when they have a similar size. We established a level of confidence in our catalog and distinct between likely and very likely pairs of craters. We compared our results according to their main-to-secondary diameter ratio, the separation between the craters, the morphological classification of the binary system [7] and the orientation of the line that connects the center of both craters. We also found ranges for the sizes of the impactors which formed the binary craters.RESULTSWe identified 39 and 18 synchronous impacts on the surfaces of Ceres and Vesta, respectively. Some examples are shown in Fig. 1, in which the contact between all rim pairs is characterized by a continuous septum without any visible stratigraphic relationship, as well as a similar preservation state, thus indicating a very likely synchronous formation. We note that in the case of the pairs on Vesta presented here, an excess of ejecta material is visible in the direction of the septum, which is expected in the case of a binary asteroid impact [7].Fig. 1. Examples of binary craters identified on the surface of Ceres (top) and Vesta (bottom). Background imagery: LAMO mosaicWe compared the orientation of the binary crater with the numerical simulations considering a population of binary asteroids with zero obliquity impacting a surface. We performed a two-sample Kolmogorov-Smirnov test [8] to determine if the distribution of the observed and simulated orientation is similar (null hypothesis). We found that for values of significance level between 0.01 and 0.2, the D-statistic resulting from the tests on both Ceres and Vesta is always higher than the significance level. Hence, there is a significant difference between the distributions of the simulations and the observations. These results support what was found by a previous study on Mars [8]: binary craters on planetary surfaces cannot be explained by a population of binary asteroids with zero obliquity.SUMMARY AND OUTLOOKOur findings are consistent with well-separated and similarly-sized binary asteroids. Additionally, comparing our catalogs with numerical simulations indicates a non-zero obliquity. A population with these characteristics remains to be observed, as suggested by a previous study of binary craters identified on Mars.Considering the recent discoveries of unexpected satellites (e.g., around Dinkinesh and Arecibo, during Lucy flyby and using Gaia astrometry [9]), the current census of binary asteroid systems is likely biased. Future observations using for instance astrometry or stellar occultations may reveal satellites that have so far remained beyond the reach of direct imaging, light curves, and radar echoes [10,11].REFERENCES[1] Benner et al., 2015; [2] Pravec et al., 2006; [3] Zeilnhofer & Barlow, 2021a; [4] Liu et al., 2018; [5] Russell et al., 2015; [6] Zeilnhofer & Barlow, 2021b; [7] Miljkovic et al., 2013; [8] Vavilov et al., 2022; [9] Tanga et al., 2023; [10] Pravec & Scheirich, 2012; [11] Segev et al., 2023.

We consider dynamical environments of (486958) Arrokoth, focusing on both their present state and their long-term evolution, starting from the KBO's formation. Both analytical (based on an upgraded Kepler-map formalism) and numerical (based on massive simulations and construction of stability diagrams in the 3D setting of the problem) approaches to the problem are used. The debris removal is due to either absorption by the KBO or by leaving the Hill sphere; the interplay of these processes is considered. The clearing mechanisms are explored, and the debris removal timescales are estimated. We assess survival opportunities for any debris orbiting around Arrokoth. The generic chaotization of Arrokoth's circumbinary debris disk's inner zone and generic cloudization of the disk's periphery, which is shown to be essential in the general 3D case, naturally explains the current absence of any debris in its vicinities.

Over the last decades, a significant number of small asteroids (diameter < 10 km) having a satellite in orbit around them have been discovered. This population of binary asteroids has very specific properties (secondary-to-primary diameter ratio of about 0.3, semi-major axis to primary diameter ratio around 2 and an obliquity of the system close to either 0 degrees or 180 degrees) pointing at formation by YORP-induced spin-up and rotational fission. When impacting the surface of terrestrial bodies, those exotic objects lead to the formation of binary craters, exhibiting various morphologies depending on the configuration of the system at the moment of the impact. Planetary surfaces constitutes therefore the best (if not the only one) record of binary asteroid population through time. In contrast to the Moon or Mercury, a large fraction of impact craters on Mars exhibits thick ejecta layers due to the presence of volatile material at the moment of the impact (e.g., water ice). The martian surface represents thus the ideal case to survey for the existence of binary craters, as the ejecta morphology can attest of a synchronous impact. From a survey of 87% of Mars surface, we identify 150 binary craters (0.5% of the total), likely formed by the impact of binary asteroids. The properties of these craters contrast with those of the population of binary asteroids: size ratio close to unity, large separation, and isotropic orientation on the surface. We run numerical simulations of impacts to test whether tidal effects on the impact trajectory can explain these discrepancies. Our results suggest that a population of similarly-sized and well-separated binary asteroids with non-zero obliquity remains to be observed.

This paper presents a robust linear method for impact probability estimation of near-Earth asteroids with the Earth. This method is a significantly modified and improved method, which uses a special curvilinear coordinate system associated with the nominal orbit of an asteroid. One of the coordinates of this system is the mean anomaly in the osculating orbit of an asteroid. A normal distribution of errors of coordinates and velocities of this system is assumed. Because of the usage of the curvilinear coordinate system, the fact that the confidence region is curved and stretched mainly along the nominal asteroid orbit is taken into account. On the main axis of the curvilinear confidence ellipsoid the virtual asteroid, which is the closest to the Earth, is found. The part of the curvilinear confidence ellipsoid, around the found virtual asteroid, is obtained and mapped on to its target plane. The impact probability is calculated as the probability of the asteroid being in the region of the found virtual asteroid multiplied by the probability of a collision of the found virtual asteroid with the Earth. This approach is shown to give more accurate and trustworthy results than the target plane method.

ABSTRACT Asteroid 1I/’Oumuamua is the first observed interstellar object. Its light-curve amplitude indicates that the object is highly elongated with an axial ratio of at least 5:1. The absence of such elongated asteroids in the Solar system and the apparent lack of observed interstellar objects are intriguing problems. Here we show that ’Oumuamua may have originated as a slightly elongated asteroid about 500 × 300 m in size. Surface erosion, caused by interstellar dust bombardment, subsequently increased the axial ratio. Simply travelling through the interstellar medium for 0.03 to 2 Gyr would have sufficed to give 1I its present shape. Passing through a 10 pc dust cloud with a grain density of 10−23 g cm−3 at 50 km s−1 would have had a similar effect on ’Oumuamua’s form. Smaller objects of around 100 m in diameter can travel the Galactic disc for merely 30 Myr before they are disrupted. This could explain the small number of interstellar objects observed to date.