The population of natural objects in a 1:1 mean motion resonance with Earth are known as Earth's co-orbitals. Main belt objects can dynamically evolve into Earth co-orbitals but taxonomic studies of some of them have suggested that they are more likely to be lunar material. While it has long been known that lunar ejecta can achieve Earth co-orbital status, in this work we calculate their expected steady-state size-frequency distribution from the impact rate of asteroids and comets on the Moon's surface, the ejecta's size-frequency and speed distribution, and dynamical integration of the particles for millions of years, among other factors. We also classify known and synthetic co-orbitals by their regime (quasi-satellite, horseshoe, tadpole, or compound) and compute the probability of transitions between them. Our nominal solution predicts that there are ≳ 70 Earth co-orbitals in the steady-state population larger than 10 m in diameter with a lunar provenance but there are orders-of-magnitude systematic uncertainty on the value. We used NEOMOD3 to calculate that about 1600 are expected in the co-orbital population with a main belt provenance and they have higher eccentricity and inclination than those from the Moon. New taxonomic classifications for more Earth co-orbitals will reduce the uncertainties on e.g. crater scaling relations that will, in turn, reduce the uncertainties in the calculation of the steady-state population of Earth's co-orbitals with a lunar origin. The mineralogy and abundance of Earth's co-orbitals is also of interest to commercial asteroid mining ventures because they are the lowest Δv targets in the asteroid population.

This work is dedicated to debias the Near-Earth Objects (NEO) population based on observations from the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescopes. We have applied similar methods used to develop the recently released NEO model generator (NEOMOD), once debiasing the NEO population using data from Catalina Sky Survey (CSS) G96 telescope. ATLAS is composed of four different telescopes. We first analyzed observational data from each of all four telescopes separately and later combined them. Our results highlight main differences between CSS and ATLAS, e.g., sky coverage and survey power at debiasing the NEO population. ATLAS has a much larger sky coverage than CSS, allowing it to find bright NEOs that would be constantly "hiding" from CSS. Consequently, ATLAS is more powerful than CSS at debiasing the NEO population for H $\lesssim$ 19. With its intrinsically greater sensitivity and emphasis on observing near opposition, CSS excels in the debiasing of smaller objects. ATLAS, as an all sky survey designed to find imminent hazardous objects, necessarily spends a significant fraction of time looking at places on the sky where objects do not appear, reducing its power for debiasing the population of small objects. We estimate a NEO population completeness of $\approx$ 88%$^{+3\%}_{-2\%}$ for H $<$ 17.75 and $\approx$ 36%$^{+1\%}_{-1\%}$ for H $<$ 22.25. Those numbers are similar to previous estimates (within error bars for H $<$ 17.75) from CSS, yet, around 3% and 8% smaller at their face values, respectively. We also confirm previous finding that the $\nu_6$ secular resonance is the main source of small and faint NEOs at H = 28, whereas the 3:1 mean motion resonance with Jupiter dominates for larger and brighter NEOs at H = 15.

We describe observations and physical characteristics of Earth-crossing asteroid 2024 YR 4 , discovered on 2024 December 27 by the Asteroid Terrestrial-impact Last Alert System. The asteroid has semimajor axis a = 2.52 au, eccentricity e = 0.66, inclination i = 3 . ° 41, and a ∼0.003 au Earth minimum orbit intersection distance. We obtained g -, r -, i -, and Z -imaging with the Gemini South/Gemini Multi-Object Spectrograph on 2025 February 7 and Y and J imaging with the Keck/Multi-Object Spectrometer for Infrared Exploration on 2025 February 12. We measured a g − i spectral slope of 13% ± 3%/100 nm and color indices g −​ r = 0.70 ± 0.10, r − i = 0.25 ± 0.06, i − Z = −0.27 ± 0.10, and Y − J = 0.41 ± 0.10. 2024 YR 4 has a spectrum that best matches R-type and Sa-type asteroids and a diameter of ∼30–65 m using our measured absolute magnitude of 23.9 ± 0.3 mag and assuming an albedo of 0.15–0.4. The lightcurve of 2024 YR 4 shows ∼0.4 mag variations with a rotation period of ∼1170 s. We use photometry of 2024 YR 4 from Gemini and other sources taken between 2024 December to 2025 February to determine the asteroid’s spin vector and shape, finding that it has an oblate, ∼3:1 axial ratio and a pole direction of λ , β = ∼ 42 ∘ , ∼−25 ∘ . Finally, we compare the orbital elements of 2024 YR 4 with the near-Earth object population model and find that its most likely sources are resonances between the inner and central Main Belt.

Near-Earth object (NEO) 1998 KY _26 is a target of the Hayabusa2# spacecraft, which it will rendezvous with in 2031 July. The asteroid has been noted to rotate rapidly and has a large out-of-plane nongravitational acceleration. We present observations consisting of deep- g - and R -band imaging obtained with the Keck I/Low Resolution Imaging Spectrometer (LRIS) and visible spectroscopy from Gemini North/Gemini Multi-Object Spectrograph (GMOS) taken of 1998 KY _26 on 2024 June 8–9 when the asteroid was ∼0.037 au from the Earth. The asteroid does not show evidence of a dust coma and has a surface brightness profile similar to nearby background stars in the deep images. The spectrum of 1998 KY _26 from the combined LRIS and GMOS observations most closely resembles Xe-type asteroids, possessing a spectral slope of 6.71% ± 0.43% 100 nm ^−1 , and color indices g – r = 0.63 ± 0.03, r – i = 0.15 ± 0.03, i – z = 0.05 ± 0.04, and implies a diameter of ∼10 m. From our deep image stacks, we compute a 3 σ upper limit on the dust production of 1998 KY _26 of <10 ^−5 kg s ^−1 , <10 ^−2 kg s ^−1 , and <10 ^−1 kg s ^−1 assuming μ m, mm, and cm size dust particles. In addition, we compare the orbit of 1998 KY _26 and other known asteroids with large nongravitational parameters to NEO population models and find that the majority, including 1998 KY _26 , likely originated from the inner Main Belt, while the second most numerous group originates from the outer main belt, followed by a third group possibly originating from the Jupiter Family Comet population. Given its inner Main Belt origin, its Xe-type spectrum, and rapid rotation, we hypothesize that the nongravitational acceleration of 1998 KY _26 may be caused by the shedding of large dust grains from its surface due to its rotation rather than H _2 O vapor outgassing.

This work examines the plausibility of a lunar origin of natural objects that have a negative total energy with respect to the geocenter, i.e. E-T =potential+ kinetic energy< 0, while they are within 3 Earth Hill radii (R-H), a population that we will refer to as 'bound'. They are a super-set of the informally named population of 'minimoons' which require that the object make at least one orbit around Earth in a synodic frame rotating with Earth and that its geocentric distance be < R-H at some point while E-T <0. Bounded objects are also a dynamical subset of the population of Earth's co-orbital population, objects in a 1:1 mean motion resonance with Earth or, less specifically, on Earth-like orbits. Only two minimoons have been discovered to date, 2006 RH120 and 2020 CD3, while 2024 PT5 and 2022 NX(1 )meet our condition for 'bound'. The likely source region of co-orbital objects is either the MB of asteroids, lunar ejecta, or a combination of both. Earlier works found that dynamical evolution of asteroids from the MB could explain the observed minimoon population, but spectra of 2020 CD(3 )and 2024 PT5 and Earth co-orbital (469219) Kamo'oalewa are more consistent with lunar basalts than any MB asteroid spectra, suggesting that the ejection and subsequent evolution of material from the Moon's surface contributes to the minimoon and, more generally, Earth's co-orbital population. This work numerically calculates the steady-state size-frequency distribution of the bound population given our current understanding of the lunar impact rate, the energy of the impactors, crater-scaling relations, and the relationship between the ejecta mass and speed. We numerically integrate the trajectory of lunar ejecta and calculate the statistics of 'prompt' bounding that take place immediately after ejection, and 'delayed' bounding that occurs after the objects have spent time on heliocentric orbits. A sub-set of the delayed bound population composes the minimoon population. We find that lunar ejecta can account for the observed population of bound objects but uncertainties in the crater formation and lunar ejecta properties induce a many orders of magnitude range on the predicted population. If the bound objects can be distinguished as lunar or asteroidal in origin based on their spectra it may be possible to constrain crater formation processes and the dynamical and physical evolution of objects from the MB into near-Earth space.

Imminent impactors may be detected only a few hours before their impact with Earth, providing a brief opportunity to characterize them before impact. We describe the characterization of imminent impactor 2024 RW _1 , which was discovered by the Catalina Sky Survey on 2024 September 4 at 05:43 UTC, before it entered the atmosphere near the northern Philippines at 16:39 UTC. We observed 2024 RW _1 with the Astrophysical Research Consortium Telescope Imaging Camera on the Apache Point Astrophysical Research Consortium’s 3.5 m telescope on 2024 September 4 at 10:16 UTC. We obtained g , r , i , and z photometry of 2024 RW _1 , yielding color indices of g – r = 0.47 ± 0.04, r – i = 0.13 ± 0.04, i – z = –0.11 ± 0.07, and g – i = 0.60 ± 0.04, corresponding to a spectral slope of 0.67 ± 0.40 %/100 nm. The closest match to an asteroid spectral type is with B-type asteroids from the C complex. We detect variations in the time-series photometry of the asteroid with an amplitude of ∼0.75, and a double-peaked rotation period of ∼1900 s. Assuming a visible albedo of 0.07 ± 0.03, a density of ∼1500 kg m ^−3 , and a calculated absolute magnitude of 30.92 ± 0.05, we estimate that the asteroid has a diameter of 3.3 ± 0.7 m and a total mass of ∼28,000 kg. Comparing our astrometric orbital solutions to NEOMOD3, the most likely source of 2024 RW _1 is the 3:1 main-belt mean-motion resonance (77% probability) followed by the ν _6 resonance (13% probability), consistent with its organic B-type nature.

Minimoons are asteroids that become temporarily captured by the Earth–Moon system. We present the discovery of 2024 PT _5 , a minimoon discovered by the Asteroid Terrestrial-impact Last Alert System Sutherland telescope on 2024 August 7. The minimoon with heliocentric semimajor axis, a ~ 1.01 au, and perihelion, q ~ 0.99 au, became captured by the Earth–Moon system on 2024 September 29 and left on 2024 November 25 UTC. Visible g , r , i , and Z spectrophotometry was obtained using Gemini North/Gemini Multi-Object Spectrograph on 2024 September 27. The color indices are g − r = 0.58 ± 0.04, r − i = 0.29 ± 0.04, and i​​​​​​ ​ − Z = −0.27 ± 0.06, and the spectrum best matches lunar rock samples followed by S-complex asteroids. Assuming an albedo of 0.21 and using our measured absolute magnitude of 28.64 ± 0.04, 2024 PT _5 has a diameter of 5.4 ± 1.2 m. We also detect variations in the lightcurve of 2024 PT _5 with a 0.28 ± 0.07 mag amplitude and a double-peaked period of ~2600 ± 500 s. We improve the orbital solution of 2024 PT _5 with our astrometry and estimate the effect of radiation pressure on its deriving an area-to-mass ratio of 7.02 ± 2.05 × 10 ^−5 m ^2 kg ^−1 , implying a density of ~3.9 ± 2.1 g cm ^−3 , compatible with having a rocky composition. If we assume 2024 PT _5 is from the near-Earth object (NEO) population, its most likely sources are resonances in the inner Main Belt when we compare its orbit with the NEO population model though this does not exclude a lunar origin.

Near-sun sky twilight observations allow for the detection of asteroids interior to the orbit of Venus (Aylos) and the Earth (Atiras) and comets. We present the results of observations with the Palomar 48-inch telescope (P48)/Zwicky Transient Facility (ZTF) camera in 30 s r-band exposures taken during evening astronomical twilight from 2019 Sep 20 to 2022 March 7 and during morning astronomical twilight sky from 2019 Sep 21 to 2022 Sep 29. More than 21,940 exposures were taken in evening astronomical twilight within 31 degrees and 66 degrees from the Sun with an r-band limiting magnitude between 18.0 and 20.8 (5th to 95th percentile), and more than 24,370 exposures were taken in morning astronomical twilight within 31 degrees and 65 degrees from the Sun with an r-band limiting magnitude between 18.2 and 20.9 (5th to 95th percentile). The morning and evening twilight pointings show a slight seasonal dependence in limiting magnitude and ability to point closer towards the Sun, with limiting magnitude improving by 0.5 magnitudes during the summer months and Sun-centric angular distances as small as 31-32 degrees during the spring and fall months. In total, the one Aylo, (594913) 'Ayl & oacute;'chaxnim, and 4 Atiras, 2020 OV1, 2021 BS1, 2021 PB2, and 2021 VR3, were discovered in evening and morning twilight observations. Additional twilight survey discoveries also include 6 long period comets: C/2020 T2, C/2020 V2, C/2021 D2, C/2021 E3, C/2022 E3 and C/2022 P3, and two short period comets: P/2021 N1 and P/2022 P2 using deep learning comet detection pipelines. The P48/ZTF twilight survey also recovered 11 known Atiras, one Aylo, three short period comes, two long period comets, one interstellar object, 45,536 Main Belt asteroids, and 265 near-Earth objects. Additionally, observations from the GROWTH network of telescopes were used to recover the Aylo, Atira, and comet discoveries made during the ZTF twilight survey. Lastly, we discuss the future twilight surveys for the discovery of Aylos such as with the Vera Rubin Observatory which will have a twilight survey starting in its first year of operations and will cover the sky as within 45 degrees from the Sun. Twilight surveys such as those by ZTF and future surveys will provide opportunities for the discovery of asteroids inside the orbits of the terrestrial planets that would otherwise be unavailable in conventional sky survey observations.

ABSTRACT The rotational properties of ∼10-m-scale asteroids are poorly understood with only a few measurements. Additionally, collisions or thermal recoil can spin their rotations to periods less than a few seconds obfuscating their study due to the observational cadence imposed by the long read-out times of charge-coupled device imagers. We present a method to measure the rotation periods of 10-m-scale asteroids using the target of opportunity capability of the Canada–France–Hawaii Telescope (CFHT) and its MegaCam imager by intentionally streaking their detections in single exposures when they are at their brightest. Periodic changes in brightness as small as ∼0.05 mag along the streak can be measured as short as a few seconds. Additionally, the streak photometry is taken in multiple g, r, and i filter exposures enabling the measurement of asteroid colours. The streak photometry method was tested on CFHT observations of three 10-m-scale asteroids, 2016 GE1, 2016 CG18, and 2016 EV84. Our three targets are among the smallest known asteroids with measured rotation periods/colours having some of the shortest known rotation periods. We compare our rotation period and taxonomic results with independent data from the literature and discuss applications of the method to future small asteroid observations.

Janus is a NASA SIMPLEx mission currently in Phase B. The SIMPLEx program is designed around the idea of using secondary launch opportunities to explore interplanetary destinations. The Janus mission concept plans to take advantage of the NASA Psyche launch to send two spacecraft to fly by Near Earth Objects of interest. A specific point design has been developed that sends two spacecraft to two binary asteroid systems, (175706) 1996 FG3 and (35107) 1991 VH, both of which have been observed repeatedly with photometry, spectrometry and radar. The Janus mission sends light-weight, low-cost spacecraft built by Lockheed Martin to encounter these high-science value small body targets. The science instruments are a visible and IR imager, from Malin Space Science Systems. The spacecraft will perform a rigorous remote sensing campaign when the object is a point source, and when resolved. The spacecraft will track the binary asteroid systems through closest approach, allowing for a combination of absolute surface resolution, relative resolution across the target asteroids and phase angle coverage unparalleled in previous asteroid flyby missions. Janus science will combine flyby observations of the target binary asteroids with ground-based observations, enabling the high resolution imaging and thermal data to be placed into a global context and leveraging all available data to construct an accurate topographical and morphological model of these bodies. Based on these measurements, the formation and evolutionary implications for small rubble pile asteroids will be studied. The science team members all have experience on asteroid missions or have made extensive ground based observations of NEAs. The industry team has extensive experience in the design, fabrication and operation of interplanetary spacecraft and instrumentation.Acknowledgements: The Janus mission is supported by NASA under a contract from the SIMPLEx Program Office. Part of this research was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.

We present a new procedure to identify observations of known objects in large data sets of unlinked detections. It begins with a Keplerian integrals method that allows us to link two tracklets, computing preliminary orbits, even when the tracklets are separated in time by a few years. In the second step, we represent the results in a `graph' where the tracklets are the nodes and the preliminary orbits are the edges. Then, acceptable `3-cycles' are identified and a least squares orbit is computed for each of them. Finally, we construct sequences of $n \geq 4$ tracklets by searching through the orbits of nearby 3-cycles and attempting to attribute the remaining tracklets. We calculate the technique's efficiency at identifying unknown objects using real detections that attempt to mimic key parameters of the Minor Planet Center's Isolated Tracklet File (ITF) and then apply the procedure to the ITF to identify tens of thousands of new objects.

We present a new procedure to identify observations of known objects in large data sets of unlinked detections. It begins with a Keplerian integrals method that allows us to link two tracklets, computing preliminary orbits, even when the tracklets are separated in time by a few years. In the second step, we represent the results in a ‘graph’ where the tracklets are the nodes and the preliminary orbits are the edges. Then, acceptable ‘3-cycles’ are identified and a least squares orbit is computed for each of them. Finally, we construct sequences of n≥4 tracklets by searching through the orbits of nearby 3-cycles and attempting to attribute the remaining tracklets. We calculate the technique’s efficiency at identifying unknown objects using real detections that attempt to mimic key parameters of the Minor Planet Center’s (MPC) Isolated Tracklet File (ITF) and then apply the procedure to the ITF. This procedure enables the recovery of several orbits, despite some having few tracklets per apparition. The MPC accepted >95% of our linkages and most of the non-accepted linkages are 2-apparition linkages even when those linkages contained more than half a dozen tracklets.

Our previous model (NEOMOD2) for the orbital and absolute magnitude distribution of Near Earth Objects (NEOs) was calibrated on the Catalina Sky Survey observations between 2013 and 2022. Here we extend NEOMOD2 to include visible albedo information from the Wide-Field Infrared Survey Explorer. The debiased albedo distribution of NEOs can be approximated by the sum of two Rayleigh distributions with the scale parameters pV,dark≃0.03 and pV,bright≃0.17. We find evidence for smaller NEOs having (on average) higher albedos than larger NEOs; this is likely a consequence of the size-dependent sampling of different main belt sources. These inferences and the absolute magnitude distribution from NEOMOD2 are used to construct the debiased size distribution of NEOs. We estimate 830±60 NEOs with diameters D>1 km and 20,000±2,000 NEOs with D>140 m. The new model, NEOMOD3, is available via the NEOMOD Simulator – an easy-to-operate code that can be used to generate user-defined samples (orbits, sizes and albedos) from the model.

Catalina Sky Survey (CSS) is a major survey of Near-Earth Objects (NEOs). In a recent work, we used CSS observations from 2005–2012 to develop a new population model of NEOs (NEOMOD). CSS's G96 telescope was upgraded in 2016 and detected over 10,000 unique NEOs since then. Here we characterize the NEO detection efficiency of G96 and use G96's NEO detections from 2013–2022 to update NEOMOD. This resolves previous model inconsistencies related to the population of large NEOs. We estimate there are 936±29 NEOs with absolute magnitude H<17.75 (diameter D>1 km for the reference albedo pV=0.14) and semimajor axis a<4.2 au. The slope of the NEO size distribution for H=25–28 is found to be relatively shallow (cumulative index ≃2.6) and the number of H<28 NEOs (D>9 m for pV=0.14) is determined to be (1.20±0.04)×107, about 3 times lower than in Harris & Chodas (2021). Small NEOs have a different orbital distribution and higher impact probabilities than large NEOs. We estimate 0.034±0.002 impacts of H<28 NEOs on the Earth per year, which is near the low end of the impact flux range inferred from atmospheric bolide observations. Relative to a model where all NEOs are delivered directly from the main belt, the population of small NEOs detected by G96 shows an excess of low-eccentricity orbits with a≃1–1.6 au that appears to increase with H (≃30% excess for H=28). We suggest that the population of very small NEOs is boosted by tidal disruption of large NEOs during close encounters to the terrestrial planets. When the effect of tidal disruption is (approximately) accounted for in the model, we estimate 0.06±0.01 impacts of H<28 NEOs on the Earth per year, which is more in line with the bolide data. The impact probability of a H<22 (D>140 m for pV=0.14) object on the Earth in this millennium is estimated to be ≃4.5%.

IntroductionSmall solar system objects may occasionally become captured temporarily by planets. Theoretical models (Granvik et al. 2012, Fedorets et al. 2017) predict the existence of a steady-state population of these objects, also known as minimoons, also in the Earth-Moon system. Only one minimoon, 2006 RH120 has been discovered until recently (Kwiatkowski et al. 2009). Since minimoons spend a significant amount of time in Earth’s vicinity, they have been identified as outstanding targets for in situ exploration, or test cases for initial steps of asteroid resource utilisation (Granvik et al. 2013, Chyba et al. 2014, Brelsford et al. 2016, Jedicke et al. 2018). Moreover, not only are minimoons outstanding targets to constrain the size-frequency distribution of metre-sized asteroids (Harris & D’Abramo 2015, Granvik et al. 2016, Tricarico 2017, Brown et al. 2002), but also for studying the structure of the smallest asteroids. However, until now, the observational evidence of the minimoon population has been lacking.ObservationsThe object 2020 CD3 was discovered on February 15th 2020 at the Mt. Lemmon station of the Catalina Sky Survey, and was noticed to be on a geocentric orbit the following night. We report the results of the astrometric and photometric observational campaign to characterise 2020 CD3 performed by Gemini North, LDT, NOT, CFHT, CSS, and other telescopes during spring 2020. By investigating the solar radiation pressure signature on the astrometry of 2020 CD3, and broad-band photometry, we present evidence that 2020 CD3 is indeed the second temporary natural satellite in the Earth-Moon system. We describe its discovery circumstances, physical characterisation, rotational period and orbital evolution.DiscussionUsing 2020 CD3 as an example case, we discuss the challenges of discovering minimoons with contemporary surveys. For the first time, we are able to compare the observational evidence of minimoons with the theoretical models. We also assess the capture duration and rotation period of 2020 CD3 in context of simulation and similar objects. Finally, we compare the origin of minimoons as captured objects from the NEO population against their origin as lunar ejecta, and show why the first mechanism is dominant.ProspectsThe discovery of 2020 CD3, and the comparison to discovery predictions with other surveys (Bolin et al. 2014), assures that the expectation of discovery of tens of minimoons with LSST is realistic (Fedorets et al. 2020). With the anticipated growth of the population of minimoons, the path for further exploration of minimoons is foreseen.ReferencesBolin et al. (2014), Icarus 241, 280Brelsford et al. (2016), PSS, 123, 4.Brown et al. (2002), Nature, 420, 294.Chyba et al. (2014) JIMO, 10(2), 477.Fedorets et al. (2017) Icarus, 285, 83.Fedorets et al. (2020), Icarus, 338, 113517.Granvik et al. (2012), Icarus, 218, 262.Granvik et al. (2013) in V. Badescu ed. Asteroids: Prospective Energy and Material Resources, 151.Granvik et al. (2016), Nature, 530, 303.Harris & D’Abramo (2015), Icarus, 257, 302.Jedicke et al. (2018) FrASS, 5, A13.Kwiatkowski et al. (2009), A&A, 495, 967.Tricarico et al. (2017), Icarus, 284, 416.

Interstellar small bodies are unique probes into the histories of exoplanetary systems. One hypothesized class of interlopers are "Jurads," exo-comets released into the Milky Way during the post-main sequence as the thermally-pulsing asymptotic giant branch (AGB) host stars lose mass. In this study, we assess the prospects for the Legacy Survey of Space and Time (LSST) to detect a Jurad and examine whether such an interloper would be observationally distinguishable from exo-comets ejected during the (pre-)main sequence. Using analytic and numerical methods, we estimate the fraction of exo-Oort Cloud objects that are released from 1-8 solar mass stars during post-main sequence evolution. We quantify the extent to which small bodies are altered by the increased luminosity and stellar outflows during the AGB, finding that some Jurads may lack hypervolatiles and that stellar winds could deposit dust that covers the entire exo-comet surface. Next, we construct models of the interstellar small body reservoir for various size-frequency distribution slopes, characteristic sizes, and the total mass sequestered in the minor planets of exo-Oort Clouds. Even with the LSST's increased search volume compared to contemporary surveys, we find that detecting a Jurad is unlikely but not infeasible given the current understanding of (exo)planet formation.

The apparent magnitude of elongated small bodies is time-dependent over their rotation phase. Therefore, previously undiscovered aspherical minor planets may experience a shape-driven selection effect in systematic surveys versus their spherical counterparts. In this study, we conduct injection-recovery exercises of synthetic asteroid lightcurves using a simple model to quantify the effect of varying axial ratio on detection efficiencies. We find that high-amplitude lightcurves are confronted with adverse selection effects for survey cadences and discovery thresholds for constructing tracklets that are representative of modern and proposed future near-Earth object searches. Furthermore, we illustrate the possible hazards of drawing population-level inferences on an underlying reservoir of elongated small bodies. If physical size and characteristic axial ratios are correlated, then size-frequency distributions may require revision at small diameters. In particular, this effect could alter the estimated populations of near-Earth objects. We conclude by discussing the applicability of our results to various other classes of solar system minor planets and interstellar interlopers, as well as discussing future work that may further interrogate this detection bias.

Ground-based characterization of spacecraft targets prior to mission operations is critical to properly plan and execute measurements. Understanding surface properties, such as mineralogical composition and phase curves (expected brightness at different viewing geometries), informs data acquisition during the flybys. Binary near-Earth asteroids (NEAs) (35107) 1991 VH and (175706) 1996 FG3 were selected as potential targets of the National Aeronautics and Space Administration’s (NASA) dual spacecraft Janus mission. We observed 1991 VH using the 3 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, on 2008 July 26. 1996 FG3 was observed with the IRTF for seven nights during the spring of 2022. Compositional analysis of 1991 VH revealed that this NEA is classified as an Sq-type in the Bus–DeMeo taxonomy classification, with a composition consistent with LL ordinary chondrites. Using thermal modeling, we computed the thermally corrected spectra for 1996 FG3 and the corresponding best-fit albedo of about 2%–3% for the best spectra averaged for each night. Our spectral analysis indicates that this NEA is a Ch-type. The best possible meteorite analogs for 1996 FG3, based on curve matching, are two carbonaceous chondrites, Y-86789 and Murchison. No rotational variation was detected in the spectra of 1996 FG3, which means there may not be any heterogeneities on the surface of the primary. However, a clear phase reddening effect was observed in our data, confirming findings from previous ground-based studies.

Near-Earth Objects (NEOs) are a transient population of small bodies with orbits near or in the terrestrial planet region. They represent a mid-stage in the dynamical cycle of asteroids and comets, which starts with their removal from the respective source regions—the main belt and trans-Neptunian scattered disk—and ends as bodies impact planets, disintegrate near the Sun, or are ejected from the solar system. Here we develop a new orbital model of NEOs by numerically integrating asteroid orbits from main-belt sources and calibrating the results on observations of the Catalina Sky Survey. The results imply a size-dependent sampling of the main belt with the ν 6 and 3:1 resonances producing ≃30% of NEOs with absolute magnitudes H = 15 and ≃80% of NEOs with H = 25. Hence, the large and small NEOs have different orbital distributions. The inferred flux of H < 18 bodies into the 3:1 resonance can be sustained only if the main-belt asteroids near the resonance drift toward the resonance at the maximal Yarkovsky rate (≃2 × 10 −4 au Myr −1 for diameter D = 1 km and semimajor axis a = 2.5 au). This implies obliquities θ ≃ 0° for a < 2.5 au and θ ≃ 180° for a > 2.5 au, both in the immediate neighborhood of the resonance (the same applies to other resonances as well). We confirm the size-dependent disruption of asteroids near the Sun found in previous studies. An interested researcher can use the publicly available NEOMOD Simulator to generate user-defined samples of NEOs from our model.

We investigate the behaviour of two recent methods for the computation of preliminary orbits. These methods are based on the conservation laws of Kepler's problem, and enable the linkage of very short arcs of optical observations even when they are separated in time by a few years. Our analysis is performed using both synthetic and real data of 822 main belt asteroids. The differences between computed and true orbital elements have been analysed for the true linkages, as well as the occurrence of alternative solutions. Some metrics have been introduced to quantify the results, with the aim of discarding as many of the false linkages as possible and keeping the vast majority of true ones. These numerical experiments provide thresholds for the metrics which take advantage of the knowledge of the ground truth: the values of these thresholds can be used in normal operation mode, when we do not know the correct values of the orbital elements and whether the linkages are true or false.