Nicholas Moskovitz

(469219) Kamo‘oalewa is the most stable Earth quasi-satellite and the target of China’s Tianwen-2 asteroid sample return mission. Due to its small size, fast rotation, and the limited observing geometry accessible from the ground, many physical properties of Kamo‘oalewa remain poorly constrained, including the rotational state and shape. We obtained three epochs of high-cadence, high signal-to-noise photometric lightcurves of Kamo‘oalewa with the Gemini North Telescope from 2026 April to May, supplemented by one lightcurve from the Lowell Discovery Telescope in 2026 May. Our analysis suggests that Kamo‘oalewa is in a non-principal-axis rotation with an elongated shape. Four possible solutions exist, including a long-axis mode (LAM) solution and a short-axis mode (SAM) solution, as well as their corresponding mirrored angular momentum directions. The most preferable solution has a LAM model with a precession period P ϕ = ( 27.65 ± 0.03 ) minutes and a rotational period P ψ = ( 50.49 ± 0.08 ) minutes , and the angular momentum points to ecliptic coordinates ( λ , β ) = (226° ± 20°, −39° ± 20°), although we cannot rule out other solutions or other close-by periods due to aliasing. We also derived a convex shape inversion for the LAM models with consistent rotational parameters but could not find a satisfactory inversion for the SAM models. The corresponding angular momentum points to ( λ , β ) = (225°, −43°), and the periods are P ϕ = 27.90 minutes and P ψ = 49.66 minutes . The non-principal-axis rotation provides additional constraints on the dynamic history or the internal structure of Kamo‘oalewa.

Context. (44) Nysa is one of the largest known E-type asteroids. Light curve inversion models have indicated that it may have an elongated shape commonly found in large binary systems. Aims. We aimed to identify the morphology and presence of possible satellites orbiting Nysa. Methods. We observed Nysa with the visible-wavelengths adaptive-optics instruments SHARK-VIS and SPHERE/ZIMPOL in order to image the object with the highest possible spatial resolution and visually identified surface features on the object. A shape model was constructed from these images and photometric light curves using the ADAM code. Results. Imaging revealed a highly unusual morphology with multiple distinct surface features, including two distinct valleys that are most easily interpreted as colli. A faint satellite was identified in the deconvolution residuals in multiple datasets. Conclusions. We determine that (44) Nysa is a binary system most likely consisting of a contact-trinary or highly-irregular, coherent primary object and a small satellite.

We present spectro-photometric griz colors for 189 near-Earth objects (NEOs) collected by the Mission Accessible Near-Earth Object Survey (MANOS). Data acquisition involved nonsimultaneous multiband exposures; thus, particular attention was given to the influence of rotational lightcurves on the derived colors. We show that colors measured without accounting for lightcurve variations can significantly influence results for individual objects and potentially introduce systematic offsets for ensemble studies. Color-based taxonomic classifications were used to investigate the distribution of spectral types. Our results were combined with other visible wavelength surveys to highlight a previously reported change in the observed taxonomic distribution of NEOs as a function of size, namely a decrease in S complex and an increase in X complex objects with increasing absolute magnitude. Plausibility arguments are given to suggest that Main Belt source region, thermal modification, discovery bias, tidal resurfacing, regolith grain size, and impact shock darkening are unlikely explanations for this size-dependent trend. Consistent with recent NEO population models and work on the connection between meteorites and young asteroid families in the Main Belt, this trend is best explained by a compositional gradient in the NEO population. In particular, the observed abundance of S complex or ordinary chondrite-like NEOs decreases by a factor of 2, from ∼65% of the population at kilometer scales down to a third at sizes ≲50 m. This result has implications for understanding the initial pre-impact population of meteorite parent bodies prior to atmospheric filtering. Furthermore, this will have implications for probabilistic impact risk assessment models.

The Mission Accessible Near-Earth Object Survey (MANOS) conducts characterization observations of objects on low delta-v orbits and in the sub-km size regime where knowledge of physical properties is sparse. Spectroscopic characterization of these objects serves to constrain the distribution of taxonomic and compositional types across the population of the most frequent Earth-impacting asteroids, including the direct precursors of meteorites. Such data can probe how spectral properties may be dependent on factors such as object size (Devogele et al. 2019), Earth encounter distance (Binzel et al. 2010), and/or perihelion distance as a proxy for peak surface temperature (Graves et al. 2019). Constraints on the ensemble spectral properties of potential Earth impactors, as well as improved understanding of how those properties evolve over time, has implications for assessing the planetary defense risk associated with the NEO population.We will present the results of MANOS spectrophotometric observations for a sample of 199 NEOs (Figures 1 and 2). Observations were performed between 2014 and 2025 from the 4.3-m Lowell Discovery Telescope (LDT), the 4.1-m Southern Astrophysical Research Telescope (SOAR), and the 4-m Mayall Telescope. At all facilities we collected images using the SDSS griz filter set with respective band centers at 0.48, 0.62, 0.76 and 0.91 microns. These multi-band data were used to derive colors and to assign a spectral taxonomic type to each object based on a down-sampling of taxonomic templates from the Bus-DeMeo system (DeMeo et al. 2009). Observing strategies were employed to constrain the lightcurves of targets, which proved necessary to properly account for rotational brightness variations during the collection of non-simultaneous images in each filter. For example, we either measured a full rotational lightcurve before collecting a color sequence, or we interleaved images in a single reference filter to track and correct for lightcurve variations (e.g. a filter sequence of seven exposures in order r-g-r-i-r-z-r). Our sample of colors accessed objects as faint as r~22, which is about 1-2 magnitudes fainter than is typically observable with spectroscopic techniques. However, the reduction of spectral information down to just four channels can limit the ability to achieve unique spectral taxonomic classifications and is not well suited to detailed compositional analysis.This work highlights several key findings. First, the distribution of taxonomic types from the color data is consistent with previously published MANOS spectroscopic results (Devogele et al. 2019). However, this distribution is distinct from analogous surveys that sample the larger end of the NEO size distribution (H20) objects.Our second major finding is related to the influence of lightcurve variations on derived colors. Our approach of non-simultaneous multi-filter imaging found that ~75% of the sample required treatment of lightcurve variability to derive reliable colors. Not accounting for this variability would produce significantly different results, where some objects would appear as part of an entirely different taxonomic complex. This would clearly have consequences for interpretation of individual objects, but also manifests as a systematic bias in the distribution of spectral types based on colors derived from non-lightcurve corrected data. Specifically, we see an over-abundance of C-complex spectral types when lightcurve variability is not treated: with lightcurve correction we find 10±5% (1-sigma) of the sample is classified as C-type, without lightcurve correction this fraction increases to 27±7%. Finding a reason for this over-abundance is an area of ongoing work. However, it is clear that lightcurve variability must be considered in any color survey that involves non-simultaneous observations across multiple filters. Of course this issue is eliminated for instruments that can obtain simultaneous multi-band images.Finally, we identified a number of unusual objects in our sample. This includes objects observed on multiple epochs that demonstrated significantly different colors across epochs. For example, the colors 2011 CG2 were best fit by a Cgh-type on one epoch and a Q-type on a second epoch. Such variability is highly unexpected and is not well understood. We also note the unusual colors of 2022 BX5, which appears as the isolated object in the upper right of Figure 2. These are the reddest colors measured for any NEO to date and are most consistent with D-type spectra that are more common in the outer Solar System.This work acknowledges funding support from NASA grants 80NSSC21K1328, NNX17AH06G, and NNX14AN82G.References:Binzel et al. (2010), Nature 463, 331.Binzel et al. (2019) Icarus 324, 41.Birlan et al. (2024) A&A 689, A334.DeMeo et al. (2009) Icarus 202, 160.Devogele et al. (2019), AJ 158:196.Graves et al. (2019), Icarus 322, 1.Ivezic et al. (2019) AJ 122, 2749.Navarro-Meza et al. (2024) AJ 167:163.Perna et al. (2018) Planetary and Space Science 157, 82.Sanchez et al. (2024) PSJ 5:131.Figure 1: Cumulative size frequency distributions of key NEO spectral surveys. The number of objects sampled by each survey are given in parentheses in the legend. MANOS generally focuses on sub-km objects (H>20). The sample for our spectrophotometric survey is shown as the bold red curve. References for each survey: MITHNEOS (Binzel et al. 2019), NEOROCKS (Birlan et al. 2024), NEOSHIELD2 (Perna et al. 2018), RATIR (Navarro-Meza et al. 2024), Sanchez et al. (2024), and MANOS spectra (Devogele et al. 2019).Figure 2: g-i versus i-z color-color plot for the 199 objects observed in the MANOS spectrophotometric survey. The taxonomic assignment for each object is indicated by the plotted letters. Data from LDT are in black, from SOAR in red, and from Mayall in yellow. The blue density contours in the background represent the colors of 223 NEOs from the Sloan Digital Sky Survey Moving...

The Near-Earth Object 2024 YR4 (hereafter YR4) was discovered by the ATLAS survey [1] on December 27 2024. With an H magnitude estimated around H = 24 [2], YR4 size is estimated to be between 40 to 90 meters [2]. At time of discovery its brightness was around 16.5 magnitude and moving across the sky at high speed. Shortly after discovery, YR4 was found to display a high probability of impacting the Earth in 2032 and was classified as a Torino scale 1 virtual impactor [3]. For a few hours to days, its visual magnitude was ideal for detailed physical characterization observations such as polarimetry or spectroscopy. However, due to the timing of its discovery during the end of the year holidays, very few observations were performed at that time. A few days later, YR4 was already a few magnitudes fainter, limiting the number of telescopes able to gather physical characterization observations. On January 7, we obtained color observations with the Lowell Discovery Telescope when YR4 was already much fainter at a V~20 magnitude. The observations showed that YR4 could potentially be an S-type or L, K-type. S-types tend to have larger albedo than L or K-type (however, very few albedo of L and K-types for NEOs have been determined). It is thus highly important to distinguish between these two taxonomic classifications. To gather more information on the composition of YR4, a Director Discretionary Proposal (DDT) was submitted to the ESO Very Large Telescope to obtain Near Infra-Red colors of YR4 using the HAWK-I instrument [4]. The proposal was submitted on Sunday January 19 at night, accepted during the day of January 20 and observed during the night of the January 20 to 21. Analysis of the NIR color dataset shows good agreement with the S or L, K-type composition, but is unfortunately not sufficient to be able to distinguish between the two. To be able to assess if YR4 is a S or L, K-type, spectroscopy in both the visible and near-infrared would be needed. Visible spectroscopy has been obtained for YR4, but no NIR spectroscopy is available. Simultaneously to the HAWK-I observations, we also obtained observations in the R band with the FORS2 instrument on the VLT. These observations were used to connect the visible colors/spectroscopy of YR4 with our new NIR colors observations. We also used these observations to obtain a high signal to noise ratio lightcurve. Our lightcurve shows a rotation period around P=19.5 minutes with an amplitude of 0.4 magnitude. [1] Tonry, J. L. et al. ATLAS: A High-cadence All-sky Survey System. PASP 130, 064505 (2018)[2] https://neo.ssa.esa.int/search-for-asteroids?sum=1&des=2024YR4[3] https://neo.ssa.esa.int/risk-list[4] Pirard, J.-F. et al. HAWK-I: A new wide-field 1- to 2.5-μm imager for the VLT. in vol. 5492 1763–1772 (2004)

The potentially hazardous asteroid 2024 YR4 (hereafter YR4) made a close approach to Earth in December 2024 through February 2025 coinciding with its discovery. During this time period, it was targeted by several ground-based telescopes and its impact probability increased above 3%, prompting action by the International Asteroid Warning Network (IAWN). As a result of this observational effort, we make use of several dense-in-time photometric lightcurves, as acquired by several ground-based observing facilities: ESO’s Very Large Telescope, the Lowell Discovery Telescope, Steward Observatory, the Danish 1.54 meter telescope, and the Nordic Optical Telescope. Photometry was acquired from these facilities using distinct astronomical filters, motivating the calculation of color transformations to a common wavelength.In addition to ground-based efforts, YR4 was targeted on 08 March by the James Webb Space Telescope’s Near Infrared Camera (JWST/NIRCam) for which photometry was acquired in the wide F150W2 and F322W2 filters [1]. Thermal emission overcomes reflected light at longer wavelengths in the F322W2 filter and introduces complications for lightcurve interpretation, thus we use the relative photometry measured in the F150W2 filter.The entire dataset constitutes high-quality measurements of YR4’s brightness over a roughly 3-month period (Figure 1). Using these lightcurves, we confirm the rotation period to be 0.324390 ± 0.000005 hours and search for plausible shape and spin state solutions. The initial efforts from a pole-scanning search using ellipsoids [2] reveals a few preferred and some unfavored regions. We use these regions in a convex shape inversion procedure to derive four candidate spin poles, with corresponding shapes, representing local best-fit solutions. We then use a MCMC routine [3] to generate a large set of viable shape and spin solutions that are consistent with our lightcurve dataset.Figure 1. Model fits to our suite of optical lightcurves from various observatories over different dates.Observations of YR4’s thermal emission with JWST’s Mid Infrared Imager (MIRI) taken on 26 March and 11 May will be used to discern between the potential shape and spin solutions. In turn, the shapes and spins will be used to constrain the size, albedo, and thermal properties of YR4. We will present the latest results at the conference, compare to other shape solutions [4], and discuss the broader implications on the origin of YR4 as well as for planetary defense strategies. Acknowledgements:The work at Ondřejov and the observations with the Danish 1.54-m telescope at La Silla were supported by "Praemium Academiae" award to P. Pravec by the Academy of Sciences of the Czech Republic, grant AP2401.References:[1] Rivkin et al. (2025) RNAAS 9, 70. [2] Muinonen et al. (2015) P&SS, 118, 227–241. [3] Muinonen et al. (2020) A&A 642, A138. [4] Bolin et al. (2025) ApJL 984 L25.

. SummaryClose to 80% of meteorites are ordinary chondrites, commonly associated with S-type asteroids [1]. However, among Near-Earth Objects (NEOs), silicate-rich S-types are no more abundant than abundant as primitive (C-, D-, and X-) types [2]. The most likely parent bodies for meteorites are small NEOs, the composition of which are not well understood. The taxonomic make-up of small NEOs is further complicated by recent meteorite recoveries corresponding to rare taxonomic types, such as the Almahata Sitta ureilite [3] and an aubrite meteorite that was formerly 2024 BX1 [4]. Here we present the results of a pilot-project in preperation for a longer program to determine the rough taxonomies of at least ∼1000 very small (absolute magnitude >25, or diameters 25. The rate of the object was also taken into consideration and limited to 1000 ”/hour to avoid trailing in calibration frames. These targets were then submitted to the LCO observing queue. Data from successful observations were reduced and calibrated using LCO’s in-house BANZAI reduction software [5]. Photometry was carried out with a simple procedure that utilizes the Python Photutils package. As part of the goals for this pilot project, we developed a pipeline to automate observations and analysis. Each step — from selecting targets from the Minor Planet Center database, submitting targets to the LCO queue, acquiring reduced, calibrated data and photometry — was carried out using this pipeline. Future work will incorporate a machine learning-based tool to assign objects to a probabilistic taxonomic classification. 3. ResultsPreliminary results, shown in Figure 1, indicate that 6 out of the 10 sampled objects exhibit colors consistent with S- and C-type classifications, evenly divided between the two. Unexpectedly, 4 objects resembled taxonomic types that are not commonly found amongst NEOs; the most surprising of these were the colors of 2025 AF and 2024 VC. 2025 AF (H = 25.10, D ≈ 28 m) shows a best match to O-type asterods. O-types are exceptionally rare, with only seven confirmed to date [6] — primarily among NEOs — with the notable exceptions of main-belt asteroid 3628 Božněmcová and potentially 7472 Kumakiri [7]. 2024 VC (H = 27.41, D ≈ 9.8 m) on the other hand did not match exactly to any known taxonomies, but fit best to A or R type asteroids. Both A- and R- types are also notably rare with 17 known A-types (mostly Inner Main Belt asteroids and Mars-crossers) and 5 R-types (4 main-belt and 1 Amor NEO) [6]. Spectrophotometric measurements such as those presented here are far more efficient than spectroscopy, but have much lower fidelity. Therefore, these colors are suggestive, but not conclusive. The relatively high fraction of uncommon taxonomic classes observed in our target sample may suggest greater diversity within the small NEO population; however, additional observations are required to substantiate this. Generally, these findings demonstrate that the MuSCAT3 and 4 instruments, along with our analysis tools, are sufficient to derive coarse taxonomies for small NEOs. Our full survey will begin on May 1, 2025. We will observe 1000 NEOs with the MuSCAT cameras through the end of 2027B. We will measure the implied compositional distribution of verysmall NEOs. Figure 1: Color-color diagram showing the colors of 10 pilot project NEOs presented here, grouped bytaxonomic class. 4. AcknowledgmentsThis work makes use of observations from the Las Cumbres Observatory global telescope network. This paper is based on observations made with the MuSCAT3 instrument, developed by Astrobiology Center and under financial supports by JSPS KAKENHI (JP18H05439) and JST PRESTO (JPMJPR1775), at Faulkes Telescope North on Maui, HI, operated by the Las CumbresObservatory. This project is supported by the Arizona Board of Regents Technology and Research Initiative Fund and by NASA YORPD award 80NSSC25K7438. References[1] Nakamura, T., Noguchi, T., Tanaka, M., et al. 2011, Itokawa Dust Particles: A Direct Link Between S-Type Asteroids and Ordinary Chondrites, Science, 333, 1113[2] Mommert, M., Trilling, D. E., Borth, D., et al. 2016, First Results from the Rapid-response Spectrophotometric Characterization of Near-Earth Objects using UKIRT, AJ, 151, 98[3] Jenniskens, P., Shaddad, M. H., Numan, D., et al. 2009, The impact and recovery of asteroid 2008 TC3, Nature, 458, 485[4] Cantillo, D. C., Ridenhour, K. I., Battle, A., et al. 2024, Laboratory Spectral Characterization of Ribbeck Aubrite: Meteorite Sample of Earth-impacting Near-Earth Asteroid 2024 BX1, , 5, 138[5] McCully, C., Turner, M., Volgenau, N., et al. 2018, LCOGT/banzai: Initial Release, 0.9.4, Zenodo[6] Bus, S. J., Binzel, R. P., & . 2002, Phase II of the Small Main-Belt Asteroid Spectroscopic Survey. A Feature-Based Taxonomy, Icarus, 158, 146[7] Burbine, T. H., Duffard, R., Buchanan, P. C., Cloutis, E. A., & Binzel, R. P. 2011, in 42nd Annual Lunar and Planetary Science Conference, Lunar and Planetary Science Conference, 2483

On 2022 September 26, NASA's DART mission intentionally impacted Dimorphos, the moon of near-Earth asteroid (65803) Didymos, changing the binary system’s orbital period. The system was studied intensively from the ground over the ensuing months until February 2023 when its brightness and low solar elongation precluded further observations. These observations revealed a clear period change of 33 minutes due to the DART impact (Thomas et al. 2023). However, there is uncertainty on whether there was a single impulsive change in the orbital period resulting in a constant post-impact value, or if there is (or was) an evolution in the period with time as the system settled into a new configuration. Careful analysis of the full post-DART lightcurve dataset (through February 2023) showed that there was insufficient data to distinguish between constant or changing post-impact orbital periods (Naidu et al. 2024, Scheirich et al. 2024). In order to understand the final outcome of the DART mission, it is therefore critical to monitor the evolution of the Didymos system prior to the European Space Agency’s Hera mission arrival in late 2026. Observations from Hera will be too far removed from the time of impact to reveal whether or not the orbit period was changing over months as the asteroid system reached a new equilibrium. Our team obtained data during 2024 June to August on Magellan (6.5-m, PI: Thomas), SOAR (4.1-m, Program ID 2024A-120042), NTT (3.6-m, PI: Snodgrass), and Faulkes Telescope South (2-m, PI: Lister), but poor weather at all sites plus Didymos’s positioning in front of the galactic plane throughout the visibility window prevented our analyses from attaining the needed sensitivity. The next visibility window occurred from late January through early March 2025, and our team was awarded time on Faulkes Telescope North (FTN, 2-m, PI: Lister), Lowell Discovery Telescope (LDT, 4.3-m, PI: Moskovitz), Palomar (5.1-m, PI: Chesley), Gemini-N (8.1-m, Program ID GN-2025A-Q-142), and Gran Telescopio Canarias (GTC, 10.4-m, PI: de Leon). Here we report on Gemini-N observations obtained on 2025 February 24, 26, and 28 when Didymos was at an apparent V magnitude about 20.3. The GTC observing run was weathered out. Observations acquired with FTN, LDT, and Palomar were successfully acquired, but are still being analyzed. Our Gemini observations were timed to optimize coverage of the Didymos binary orbit within the run and to provide complementary observations with neighboring runs scheduled on Palomar and GTC. We observed Didymos for 3.7 hr at the start of each night using the SDSS-i filter. We tracked at the sidereal rate and limited individual exposure times to 20 sec to keep the asteroid’s trailing from significantly exceeding the stellar point spread function. Images were processed using the Gemini DRAGONS pipeline (Labrie et al. 2023) and photometry was measured using Photometry Pipeline (Mommert 2017). After manually removing frames that were contaminated by nearby stars or other image artifacts, lightcurve deconvolution was performed using the binary asteroid lightcurve decomposition method as earlier Didymos datasets (Pravec et al. 2022, 2024). Our preliminary analysis finds that mutual events occurred about 70 min earlier than the nominal prediction (see Figure 1), a difference of 1.6-sigma. This yields a binary orbital period of 11.3667 +/- 0.0002 hr (3-sigma), assuming that the period has been constant since 2022/2023. With the much longer time baseline, these observations reduce the uncertainty in the binary period by about a factor of 6 compared to the previously published 3-sigma measurement of 11.3675 +/- 0.0012 hr (Scheirich et al. 2024). As expected, the data quality was insufficient to constrain Dimorphos’ rotation (which needed rms residuals of 0.004-0.007 mag, while residuals of 0.017 mag were obtained). Deep stacking of all images collected on a night did not reveal evidence of a tail or any remaining large fragments, though we have not yet quantified these non-detections. We will provide updated results on the full 2025 dataset. If ongoing analyses of the FTN, LDT, and/or Palomar datasets yield sufficiently small rms residuals, the lightcurve deconvolution will be re-run on the larger dataset, though the solution is not expected to change appreciably. The question of whether or not the orbital period has changed or if the apparently shorter period is just a statistical fluke is unlikely to be resolved from these data since they were all acquired relatively close to the Gemini observations. We plan to propose for similar observations during Didymos’s next apparition in 2026 July to attempt to resolve this question.Acknowledgements: The work at Ondřejov has been supported by the "Praemium Academiae" award by the Academy of Sciences of the Czech Republic, grant AP2401.References Labrie et al., RNAAS 7, id.214 (2023) Mommert, M. Astronomy & Computing 18, 47 (2017) Naidu et al., PSJ 5, 74 (2024) Pravec et al., PSJ 3, 175 (2022) Pravec et al., Icarus 418, id.116138 (2024) Scheirich et al., PSJ 5, 17 (2024) Thomas et al., Nature 616, 448 (2023) Figure 1: Decomposition of Didymos system lightcurve from 2025 February 24-28 (a) into signals from mutual events (b), and primary rotation (c). The top panel (a) shows the combined lightcurve over 11.37 hr. The full lightcurve can be decomposed into a contribution from the 2.260-hr rotation of Didymos (bottom panel c) and a contribution due to mutual events. The mutual events are indicated by horizontal lines underneath the lightcurve in panel (b). The blue lines are the observed mutual events (PE = primary eclipse, PO = primary occultation, SE = secondary eclipse, SO = secondary occultation), while the red lines are the nominal predictions of these same events from Scheirich et al. (2024), which occurred ~70 minutes later than observed.