Arecibo Planetary Radar Observations of Near-Earth Asteroids: 2017 December–2019 December

Self Cite

On 2020 April 29, the near-Earth object (52768) 1998 OR2 experienced a close approach to Earth at a distance of 16.4 lunar distances (LD). 1998 OR2 is a potentially hazardous asteroid of absolute magnitude H = 16.04 that can currently come as close to Earth as 3.4 LD. We report here observations of this object in polarimetry, photometry, and radar. Our observations show that the physical characteristics of 1998 OR2 are similar to those of both M- and S-type asteroids. Arecibo’s radar observations provide a high radar albedo of σ ˆ OC = 0.29 ± 0.08, suggesting that metals are present in 1998 OR2 near-surface. We find a circular polarization ratio of μ c = 0.291 ± 0.012, and the delay-Doppler images show that the surface of 1998 OR2 is a top-shape asteroid with large-scale structures such as large craters and concavities. The polarimetric observations display a consistent variation of the polarimetric response as a function of the rotational phase, suggesting that the surface of 1998 OR2 is heterogeneous. Color observations suggest an X-complex taxonomy in the Bus–DeMeo classification. Combining optical polarization, radar, and two epochs from the NEOWISE satellite observations, we derived an equivalent diameter of D = 1.80 ± 0.1 km and a visual albedo p v = 0.21 ± 0.02. Photometric and radar data provide a sidereal rotation period of P = 4.10872 ± 0.00001 hr, a pole orientation of (332.°3 ± 5°, 20.°7 ± 5°), and a shape model with dimensions of ( 2.08 − 0.10 + 0.10 , 1.93 − 0.10 + 0.10 , 1.60 − 0.05 + 0.05 ) km.

Section: Radar Observationsmentioning

confidence: 99%

“…Most of our images are sampled several times so that the image resolution is 7.5 m per pixel. For more details about radar observations, the reader can refer to Ostro (1993) and Virkki et al (2022).…”

Section: Radar Observationsmentioning

confidence: 99%

Surface Heterogeneity, Physical, and Shape Model of Near-Earth Asteroid (52768) 1998 OR2

Devogèle,

McGilvray,

MacLennan

et al. 2024

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“…The CW spectrum shows a bandwidth of 0.50 ± 0.02 Hz. Using the relation linking the bandwidth of a CW spectrum and the rotation period (see Virkki et al 2022 for more information on CW radar observations and their analysis), we estimate that the rotation period of 2016 NJ 33 is between 0.41 and 1.99 hr with a mean of 1.43 hr with 3σ confidence. We obtained this result by simulating random pole orientations and a normal distribution of the bandwidth (0.50 ± 0.02 Hz) and diameter (32 ± 3 m).…”

Section: Appendix a Rotation Period Of 2016 Nj 33mentioning

confidence: 99%

Dark Comets? Unexpectedly Large Nongravitational Accelerations on a Sample of Small Asteroids

Seligman¹,

Farnocchia²,

Micheli³

et al. 2023

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We report statistically significant detections of nonradial, nongravitational accelerations based on astrometric data in the photometrically inactive objects 1998 KY26, 2005 VL1, 2016 NJ33, 2010 VL65, 2016 RH120, and 2010 RF12. The magnitudes of the nongravitational accelerations are greater than those typically induced by the Yarkovsky effect, and there is no radiation-based, nonradial effect that can be so large. Therefore, we hypothesize that the accelerations are driven by outgassing and calculate implied H2O production rates for each object. We attempt to reconcile outgassing-induced acceleration with the lack of visible comae or photometric activity via the absence of surface dust and low levels of gas production. Although these objects are small, and some are rapidly rotating, the surface cohesive forces are stronger than the rotational forces, and rapid rotation alone cannot explain the lack of surface debris. It is possible that surface dust was removed previously, perhaps via outgassing activity that increased the rotation rates to their present-day value. We calculate dust production rates of order ∼10−4 g s−1 in each object, assuming that the nuclei are bare, within the upper limits of dust production from a sample stacked image of 1998 KY26 of M ̇ Dust < 0.2 g s−1. This production corresponds to brightness variations of order ∼0.0025%, which are undetectable in extant photometric data. We assess the future observability of each of these targets and find that the orbit of 1998 KY26—which is also the target of the extended Hayabusa2 mission—exhibits favorable viewing geometry before 2025.

“…In the recent past, the number of known binary asteroid systems has grown significantly due to improvements in observational technology and an expanded network of asteroid monitoring stations. Current assessments suggest that about 235 main-belt asteroids and 93 near-Earth asteroids (NEAs) are multiple-body systems, 3 and approximately 12% of observed NEAs between 2017 and 2019 were found to be binary asteroid systems (Virkki et al 2022). Many more binary systems are hypothesized to exist (Margot et al 2015) but simply may not be observable due to the separation of the system or the size of the satellite.…”

Section: Introductionmentioning

confidence: 99%

Categorization of Spatial and Temporal Ejecta Outcomes in Binary Systems Based on Variations of the Didymos System

Larson,

Fernandez,

Sarid

2024

With the increasing number of binary asteroid systems being discovered, ejecta studies must expand from solely investigating single-body systems to modeling more complex multiple-body systems. For example, the Double Asteroid Redirection Test provides an opportunity to study the dynamics of a debris cloud around Didymos and Dimorphos, a near-Earth binary asteroid system. Here we simulate 72 variations on the Didymos system in order to categorize types of ejecta outcomes and analyze the influence of the varying system parameters on each outcome. We have varied five parameters: the system separation, the mass ratio between the two bodies, the impact location, the target-body shape, and the target-body rotation period. The resulting provenance maps of the final ejecta distributions were blindly sorted into five categories, while the resulting cumulative distribution functions (CDFs), describing the rate at which particles hit the surface, were blindly sorted into eight categories. We count the occurrences of the parameter values in each of the categories and apply a Cramer’s V statistical test to evaluate the significance of the association between each varied effect and the overall grouping of the provenance maps and CDFs. We conclude that more dominant effects, such as a small rotation period, produce notably similar ejecta distributions that result in being assigned to the same category. Less dominant effects, such as target-body location, are sorted into several categories due to the larger influence of varying dominant effects.