NEOSM Survey Cadence and Simulation

Context. The near-Earth object (NEO) population is a window into the original conditions of the protosolar nebula, and has the potential to provide a key pathway for the delivery of water and organics to the early Earth. In addition to delivering the crucial ingredients for life, NEOs can pose a serious hazard to humanity since they can impact the Earth. To properly quantify the impact risk, physical properties of the NEO population need to be studied. Unfortunately, NEOs have a great variation in terms of mitigation-relevant quantities (size, albedo, composition, etc.) and less than 15% of them have been characterized to date.Aims. There is an urgent need to undertake a comprehensive characterization of smaller NEOs (D< 300 m) given that there are many more of them than larger objects; their small sizes make them intrinsically fainter and therefore harder to study. One of the main aims of the NEOShield-2 project (2015–2017), financed by the European Community in the framework of the Horizon 2020 program, is therefore to retrieve physical properties of a wide number of NEOs in order to design impact mitigation missions and assess the consequences of an impact on Earth.Methods. We carried out visible photometry of NEOs, making use of the DOLORES instrument at the Telescopio NazionaleGalileo(TNG, La Palma, Spain) in order to derive visible color indexes and the taxonomic classification for each target in our sample.Results. We attributed for the first time the taxonomical complex of 67 objects obtained during the first year of the project. While the majority of our sample belong to the S-complex, carbonaceous C-complex NEOs deserve particular attention. These NEOs can be located in orbits that are challenging from a mitigation point of view, with high inclination and low minimum orbit intersection distance (MOID). In addition, the lack of carbonaceous material we see in the small NEO population might not be due to an observational bias alone.

Properties and evolution of NEO families created by tidal disruption at Earth

Rotational properties of near-earth objects obtained by the IMPACTON project

Through their delivery of water and organics, near-Earth objects (NEOs) played an important role in the emergence of life on our planet. However, they also pose a hazard to the Earth, as asteroid impacts could significantly affect our civilization. Potentially hazardous asteroids (PHAs) are those that, in principle, could possibly impact the Earth within the next century, producing major damage. About 1600 PHAs are currently known, from an estimated population of 4700 ± 1450. However, a comprehensive characterization of the PHA physical properties is still missing. Here we present spectroscopic observations of 14 PHAs, which we have used to derive their taxonomy, meteorite analogs, and mineralogy. Combining our results with the literature, we investigated how PHAs are distributed as a function of their dynamical and physical properties. In general, the “carbonaceous” PHAs seem to be particularly threatening, because of their high porosity (limiting the effectiveness of the main deflection techniques that could be used in space) and low inclination and minimum orbit intersection distance (MOID) with the Earth (favoring more frequent close approaches). V-type PHAs also present low MOID values, which can produce frequent close approaches (as confirmed by the recent discovery of a limited space weathering on their surfaces). We also identified those specific objects that deserve particular attention because of their extreme rotational properties, internal strength, or possible cometary nature. For PHAs and NEOs in general, we identified a possible anti-correlation between the elongation and the rotational period, in the range of P rot ≈ 5–80 hr. This would be compatible with the behavior of gravity-dominated aggregates in rotational equilibrium. For periods ≳80–90 hr, such a trend stops, possibly under the influence of the YORP effect and collisions. However, the statistics is very low, and further observational and theoretical work is required to characterize such slow rotators.

We estimate the total population of near-Earth objects (NEOs) in the solar system using an extensive, “solar-system-to-pixels” fake-asteroid simulation to debias detections of real NEOs by the ATLAS survey. Down to absolute magnitudes H = 25 and 27.6 (diameters of ∼34 and 10 m, respectively, for 15% albedo), we find total populations of (3.72 ± 0.49) × 105 and (1.59 ± 0.45) × 107 NEOs, respectively. Most of the plausible sources of error tend toward underestimation, so the true populations are likely larger. We find the distribution of H magnitudes steepens for NEOs fainter than H ∼ 22.5, making small asteroids more common than extrapolation from brighter H mags would predict. Our simulation indicates a strong bias against detecting small but dangerous asteroids that encounter Earth with high relative velocities—i.e., asteroids in highly inclined and/or eccentric orbits. Worldwide NEO discovery statistics indicate this bias affects global NEO detection capability to the point that an observational census of small asteroids in such orbits is probably not currently feasible. Prompt and aggressive followup of NEO candidates, combined with closer collaborations between segments of the global NEO community, can increase detection rates for these dangerous objects.

Near-Earth Asteroids (NEAs) are an extremely valuable resource to study the origin and evolution of the Solar System more in depth. At the same time, they constitute a serious risk for the Earth in the not-so-remote case of an impact. In order to mitigate the hazard of a potential impact with the Earth, several techniques have been studied so far and, for the majority of them, a good knowledge about the chemical and physical composition of the target object is extremely helpful for the success of the mission. A multiple-rendezvous mission with NEAs, with close-up observations, can help the scientific community to improve the overall knowledge about these objects and to support any mitigation strategy. Because of the cost of this kind of mission in terms of Dv, a solar sail spacecraft is proposed in this study, in order to take advantage of the propellantless characteristic of this system. As part of the DLR/ESA Gossamer roadmap, and thus considering the sailcraft based on this technology, the present work is focused on the search of possible sequences of encounters, with priority on Potentially Hazardous Asteroids (PHAs). Because of the huge amount of NEAs, the selection of the candidates for a multiple rendezvous is firstly a combinatorial problem, with more than a billion of possible sequences for only three consecutive encounters. Moreover, an optimization problem should be solved in order to find a feasible solar-sail trajectory for each leg of the sequence. In order to tackle this mixed combinatorial/optimization problem, the strategy used is divided into two main steps: a sequence search by means of heuristic rules and simplified trajectory models, and a subsequent optimization phase. Preliminary results were presented previously by the authors, demonstrating that this kind of mission is promising. In this paper, we aim to find new sequences by introducing a different approach on the sequence search algorithm and by reducing the area-to-mass ratio of the solar sail. A smaller area-to-mass ratio entails either the possibility to carry on more payload or to reduce the sail area, raising the TRL. A grid search over 10 years of launching dates is carried out, resulting in different sequences of objects depending on the departing date. Two sequences are fully studied and optimized. The mission parameters and trajectories of the sequences found are shown and explained.

<p>We report 491 new near-infrared spectroscopic measurements of 420 Near-Earth Objects (NEOs) collected on NASA’s IRTF in the context of MITHNEOS (PI: DeMeo). The measurements were combined with previously published data (Binzel et al. 2019) and bias-corrected for albedo variations to derive the intrinsic compositional distribution of the overall NEO population. We also investigated individual subpopulations coming from various escape routes (ERs) in the asteroid belt by use of the dynamical model of Granvik et al. (2018). The resulting distributions reflect well the compositional gradient of the asteroid belt, with decreasing fractions of silicate-rich (S- and Q-type) bodies and increasing fractions of carbonaceous (B-, C-, D- and P-type) bodies as a function of increasing ER distance from the Sun. The compositional match between NEOs and their predicted source populations validates dynamical models used to identify ERs and argues against strong composition change in the main belt between approximately 5 km and 100 m. An exception comes from the overabundance of D-type NEOs from the 5:2J and, to a lesser extent, the 3:1J and ν6 ERs, hinting at the presence of a large population of small D-type asteroids in the main belt. Alternatively, this excess may indicate spectral evolution from D-type surfaces to C and P types due to space weathering or point to preferential fragmentation of D-types in the NEO space. No further evidence for the existence of collisional families in the main belt, below the detection limit of current main-belt surveys, was found in this work.</p>

While the physical characterization of near-Earth objects (NEOs) is progressing at a much slower rate than that of discovery, a substantial body of thermal-infrared data has been gathered over the past few years. A wide variety of taxonomic classes in the NEO population have now been sampled by means of thermal-infrared spectrophotometric observations. The resulting albedo information, together with the distribution of taxonomic types from spectroscopic investigations and the rapidly increasing catalog of orbits and absolute magnitudes derived from NEO search programs, such as LINEAR, facilitates more accurate estimates of the size distribution of the NEO population and the magnitude of the impact hazard. Despite our rapidly increasing knowledge of the NEO population, many questions and uncertainties remain, such as: How does the albedo distribution of NEOs compare with that of main-belt asteroids, and does space weathering play a role? How does the surface structure and regolith coverage of NEOs vary with size and taxonomic type? What fraction of NEOs are extinct comets? A property of particular interest is the surface thermal inertia of small asteroids, which is an indicator of the presence or lack of a thermally-insulating surface layer. Large asteroids can accumulate regolith, but can very small asteroids retain thermally-insulating collisional debris or at least a dust layer? Knowledge of thermal inertia is important for accurate calculations of the Yarkovsky effect, which can significantly influence the orbital evolution of potentially hazardous NEOs, and for the design of instruments for lander missions. Contrary to earlier expectations, evidence appears to be accumulating that even sub-kilometer asteroids often have a significant thermally-insulating surface layer. Recent results from thermal-infrared investigations of NEOs are reviewed and implications for the surface properties of small asteroids discussed.

Using the Wide Field Camera for the United Kingdom Infrared Telescope (UKIRT), we measure the near-infrared colors of near-Earth objects (NEOs) in order to put constraints on their taxonomic classifications. The rapid-response character of our observations allows us to observe NEOs when they are close to the Earth and bright. Here we present near-infrared color measurements of 86 NEOs, most of which were observed within a few days of their discovery, allowing us to characterize NEOs with diameters of only a few meters. Using machine-learning methods, we compare our measurements to existing asteroid spectral data and provide probabilistic taxonomic classifications for our targets. Our observations allow us to distinguish between S-complex, C/X-complex, D-type, and V-type asteroids. Our results suggest that the fraction of S-complex asteroids in the whole NEO population is lower than the fraction of ordinary chondrites in the meteorite fall statistics. Future data obtained with UKIRT will be used to investigate the significance of this discrepancy.

The Arecibo Observatory's legacy and future radar capabilities

Searching for the first near-Earth object family

NEEMO 15: Evaluation of human exploration systems for near-Earth asteroids

Space Rocks, such as asteroids and comets, constitute primordial remnants of the formation of our Solar System. During the last decades these objects have become increasingly available to study, particularly those that enter near-Earth space, due to the advancement of detection and follow-up techniques. With the discovery and cataloging of most Potentially Hazardous Objects (PHO), our ability to anticipate possible impacts has significantly improved. Impact cratering is an ubiquitous process in the solar system, and Earth is not exempt from this phenomena. However, detection alone is not enough: without accurate orbit prediction and knowledge of an object's physical properties, we cannot develop effective deflection strategies. In this context, the physical and dynamical characterization of near-Earth objects (NEO) has grown into a rapidly advancing field—evolving from purely cosmological interest to a cornerstone of planetary defense.For over five decades the Arecibo Observatory in Puerto Rico, served as a key facility for these studies, via its planetary radar system instrumentation. Even with the closure of the facilities, the data endures, and are available to the scientific community and continue to be of great scientific value. This work includes an effort to catalog all the objects detected at the Arecibo Observatory with its Planetary Radar System, which includes over 800 NEAs. As well as the use of some of these observations to enhance our knowledge of physical characteristics of these objects. The thesis is presented as a compilation of peer reviewed articles pertaining to the physical and dynamical characterization of a subset of NEAs observed with the AO Planetary Radar System. The first article: “Radar and Optical Characterization of Near-Earth Asteroid2019~OK”,~demonstrates the adaptability in observation scheduling and the impressive precision of the radar technique. With just a few minutes of data, the reported astrometry secured its orbit for the next two centuries. This object was found to be a very fast rotator, having a rotation period of 3-5 minutes.The next publication: “The Fastest Rotators: Near-Earth Asteroids Observed with the Arecibo Planetary Radar System", studies a subset of NEAs with rotation periods less than 10~minutes. In this work we compare optical and radar derived parameters, and find, in general, both methodologies to be in good agreement. The last publication included is: “2020 BX12-The Last Binary Asteroid Discovered at Arecibo", which presents the analysis and shape modeling of this PHA. A rotation period typical of the population, close to the spin barrier, is found for the primary. Data acquired during the 2024 apparition using the Gran Telescopio Canarias (10.4~m) provided a spectrum which is in agreement with the expected taxonomy based on the radar derived circular polarization. This research integrates radar and optical data (Figure 1) from selected NEAs to contribute to our understanding of their physical and dynamical properties. By combining both optical and radar data sets, we can cross-validate and refine our findings. Understanding their composition is essential for developing potential planetary defense strategies, should they be needed in the future. Beyond enhancing our knowledge of rapidly rotating asteroids and binary systems, this study preserves a detailed record of all observations made by the Arecibo Planetary Radar system. This catalog offers the scientific community a unique opportunity to explore and make use of the previously under-explored Arecibo data archive, unlocking new possibilities for future discoveries.Figure 1. Comparison of Measured values (Red box) for specific physical and dynamical parameters of NEA’s obtained via optical and radar observations and relationships with derived/estimated parameters (green box). Colored lines to mark parameters relationship. Arrow end direct to calculated values, open circles are derived. Solid black circles are physical or dynamical parameters.

The study of near-Earth asteroids (NEAs) is helpful for understanding the dynamics of our solar system and assessing potential impact risks to Earth. Among these, Potentially Hazardous Asteroids (PHAs) warrant particular attention due to their orbital proximity to our planet. Characterizing the physical properties of PHAs, such as their size and shape, is fundamental for hazard assessment and for planning potential mitigation strategies. Furthermore, detailed knowledge of these small bodies can offer valuable insights into the formation and evolution of the solar system. In this study we present two shape models of two distinct PHAs: 5189 (1990 UQ) and 2015 DP155.Asteroid 5189 (1990 UQ), a potentially hazardous asteroid, was found to be an interesting case study as it helped us with characterization of a mini-moon, 2022 NX1, due to polarimetric results from observations at VLT. In August 2022, it was determined from those observations that 1990 UQ and 2022 NX1 have similar properties, indicating that they should share similar albedos. This is particularly important as 2022 NX1's orbit makes it challenging to observe. Shortly after NX1's closest approach in 2022, it became visible, leading to acquisition of a visible spectrum with GranTeCan (de la Fuente et al. 2023). However, to achieve our goals of gaining insights about NX1 characteristics, precise knowledge of 1990 UQ’s physical properties is essential. Fortunately, 1990 UQ has a much longer observational history, including radar data obtained at Goldstone in May 2021, and numerous lightcurves.2015 DP155 is also a PHA and a potential spacecraft target. It has radar observations from both Arecibo and Goldstone in June 2018, as well as optical lightcurves from various facilities. Using these data for shape modeling, we find an average diameter of about 140 m (Repp et al. 2020), making it one of the smallest asteroids with a well-determined shape model. It looks approximately triangular when viewed along its rotation axis.We found 3D shape models for both of these PHAs using the SHAPE software (Magri et al. 2007) with the available radar and lightcurve data. These models offer additional insight into their physical properties, which may help in evaluating potential hazards and guiding planetary defense measures.

The current state of near-Earth asteroids (NEAs) observations shows an annual increase in the number of newly discovered objects However, the frequency distribution of NEAs by size shows a sharp decrease in the number of objects with size less than 300 m, which contradicts the results of theoretical modeling of the NEA population. Considering definition of potentially hazardous asteroids (PHA), only objects with diameters more than 140 m could pose catastrophic consequences to the Earth and mankind in general. But in the same time, impacts of smaller size objects could lead to significant consequences on local level and their large predicted number increases this probability. Due to their small size which results in faint apparent magnitude, such NEAs are discovered in a short interval of their close approach (CA) to the Earth, when their apparent magnitude are tending to be as bright as possible for a given size. This is not only facilitates the detection of such new objects but also increases their observability by small ground-based telescopes. However, apparent rate of motion during this time might exceed 10 deg d −1 making the observations challenging. The used Rotating-drift-scan CCD (RDS CCD) technique allows to get images of fast-moving objects as a point, that in turn to determine the coordinates of their image centers with sufficient astrometric precision. Obtained in current research project positions show errors in the range ± (0.2″ − 0.3″) in both coordinates with comparison both to JPL's HORIZONS 1 system and NEODyS-2 2 service. The part of observations was obtained around time moment of minimal distance to the Earth during current CA for newly discovered NEAs. Such observations are important to extend observed orbital arc for reliable improvement of their orbit determinations and reducing orbital uncertainty, so it will be possible to recover them in next apparitions.