The binary near-Earth asteroid (175706) 1996 FG3 - An observational constraint on its orbital evolution

Using our photometric observations taken between 1996 and 2013 and other published data, we derived properties of the binary near-Earth asteroid (175706) 1996 FG3 including new measurements constraining evolution of the mutual orbit with potential consequences for the entire binary asteroid population. We also refined previously determined values of parameters of both components, making 1996 FG3 one of the most well understood binary asteroid systems. We determined the orbital vector with a substantially greater accuracy than before and we also placed constraints on a stability of the orbit. Specifically, the ecliptic longitude and latitude of the orbital pole are 266{\deg} and -83{\deg}, respectively, with the mean radius of the uncertainty area of 4{\deg}, and the orbital period is 16.1508 +/- 0.0002 h (all quoted uncertainties correspond to 3sigma). We looked for a quadratic drift of the mean anomaly of the satellite and obtained a value of 0.04 +/- 0.20 deg/yr^2, i.e., consistent with zero. The drift is substantially lower than predicted by the pure binary YORP (BYORP) theory of McMahon and Scheeres (McMahon, J., Scheeres, D. [2010]. Icarus 209, 494-509) and it is consistent with the theory of an equilibrium between BYORP and tidal torques for synchronous binary asteroids as proposed by Jacobson and Scheeres (Jacobson, S.A., Scheeres, D. [2011]. ApJ Letters, 736, L19). Based on the assumption of equilibrium, we derived a ratio of the quality factor and tidal Love number of Q/k = 2.4 x 10^5 uncertain by a factor of five. We also derived a product of the rigidity and quality factor of mu Q = 1.3 x 10^7 Pa using the theory that assumes an elastic response of the asteroid material to the tidal forces. This very low value indicates that the primary of 1996 FG3 is a 'rubble pile', and it also calls for a re-thinking of the tidal energy dissipation in close asteroid binary systems.Comment: Many changes based on referees comment

Spin states of asteroids in the Eos collisional family

Eos family was created during a catastrophic impact about 1.3 Gyr ago. Rotation states of individual family members contain information about the history of the whole population. We aim to increase the number of asteroid shape models and rotation states within the Eos collision family, as well as to revise previously published shape models from the literature. Such results can be used to constrain theoretical collisional and evolution models of the family, or to estimate other physical parameters by a thermophysical modeling of the thermal infrared data. We use all available disk-integrated optical data (i.e., classical dense-in-time photometry obtained from public databases and through a large collaboration network as well as sparse-in-time individual measurements from a few sky surveys) as input for the convex inversion method, and derive 3D shape models of asteroids together with their rotation periods and orientations of rotation axes. We present updated shape models for 15 asteroids and new shape model determinations for 16 asteroids. Together with the already published models from the publicly available DAMIT database, we compiled a sample of 56 Eos family members with known shape models that we used in our analysis of physical properties within the family. Rotation states of asteroids smaller than ~20 km are heavily influenced by the YORP effect, whilst the large objects more or less retained their rotation state properties since the family creation. Moreover, we also present a shape model and bulk density of asteroid (423) Diotima, an interloper in the Eos family, based on the disk-resolved data obtained by the Near InfraRed Camera (Nirc2) mounted on the W.M. Keck II telescope.Comment: Accepted for publication in ICARUS Special Issue - Asteroids: Origin, Evolution & Characterizatio

Photometry of the Didymos System across the DART Impact Apparition

On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes. Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite’s orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from 2022 July to 2023 February. We focus here on decomposable lightcurves, i.e., those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the postimpact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ∼1 day after impact and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days postimpact. This bulk photometric behavior was not well represented by an HG photometric model. An HG 1 G 2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least 2023 March. Its persistence implied ongoing escape of ejecta from the system many months after DART impact

Asteroids 87887 – 415992: the youngest known asteroid pair?

Context. Pairs of asteroids, that is, couples of single bodies on tightly similar heliocentric orbits, were recently postulated as a new category of objects in the solar system. They are believed to be close twins to binary and multiple systems. Aims. Ages of the known pairs range from about 15 kyr to nearly a million years. Beyond the upper limit, the pairs disperse in the background population of asteroids and become difficult to detect. Below the lower limit, the pairs should be easily recognizable if they exist and are discovered by surveys. Using the available data, we analyze the possible existence of very young asteroid pairs with clearly proven ages ≤ 10 kyr. Methods. We searched for candidate very young asteroid pairs in the current catalog of asteroid orbits. After a preliminary analysis, we selected the most promising case of the small asteroids (87887) 2000 SS286 and (415992) 2002 AT49. We collected photometric observations to determine their rotation periods and absolute magnitudes. Results. The rotation period of (87887) 2000 SS286 is 5.7773 ± 0.0004 h. Analysis of the data for (415992) 2002 AT49 indicates as the most probable period 2.6366 ± 0.0003 h, but other solutions are still possible. The composite light curves of the two asteroids have very low amplitudes, 0.22 and 0.12 mag, suggesting roundish shapes. Our observations also allow us to determine the absolute magnitude in R band HR = 14.99 ± 0.04 and HR = 16.24 ± 0.03 for the primary and secondary components. A transformation to the visible band provides H = 15.44 ± 0.05 and H = 16.69 ± 0.04. These two asteroids experienced a very close encounter, probably a formation event, some 7.4 ± 0.3 kyr ago. The formal extension of our numerical runs backward in time reveal that these close encounters may have continued, starting from ≃ 45 kyr ago. However, based on tests using synthetic fission events, we argue that the older age solutions might be the true solution only at ≃ (10−15)% level, assuming their low initial separation velocity is of between 10−20 cm s-1. This means that 87887–415992 probably is the youngest known asteroid pair in our dataset with a reliable determined age

(Non-)detection of a quadratic drift in mean anomaly of the satellite of 1996 FG3

We present an analysis of photometric observations of binary Near-Earthasteroid (175706) 1996 FG3, observed from 1996 to 2011. The analysis gave two possible solutions for a quadratic drift of mean anomaly of the satellite, (0.0 +0.12/-0.2 deg/yr2 and ~ 12 deg/yr2. We expect to resolve between the two solutions, and to further constrain the uncertainty, using new observations obtained during 2011

(Non-)detection of a quadratic drift in mean anomaly of the satellite of 1996 FG3

We present an analysis of photometric observations of binary Near-Earthasteroid (175706) 1996 FG3, observed from 1996 to 2011. The analysis gave two possible solutions for a quadratic drift of mean anomaly of the satellite, (0.0 +0.12/-0.2 deg/yr2 and ~ 12 deg/yr2. We expect to resolve between the two solutions, and to further constrain the uncertainty, using new observations obtained during 2011

Rotation state of 495 Eulalia and its implication

Context. The low-albedo part of the Nysa-Polana-Hertha asteroid complex has recently been found to consist of at least two families. The larger of them has been associated with asteroid 495 Eulalia, hereafter named the Eulalia family. The unstable location of this body very close to Jupiter’s 3:1 mean motion resonance (J3/1 resonance) at the periphery of the associated family in the space of proper orbital elements makes this case peculiar. Aims. We consider the possibility that 495 Eulalia was originally positioned farther from the J3/1 resonance when the family formed via a catastrophic impact than it is today. It was then transported to its current orbit by the Yarkovsky thermal forces over hundreds of millions of years. This requires that 495 Eulalia had a prograde rotation state. Methods. We use photometric observations and lightcurve inversion methods to determine the rotation pole of 495 Eulalia. Numerical simulation accounting for perturbations from the Yarkovsky effect then reveals the possible pathways of Eulalia orbital evolution. Results. We find that both of the possible pole solutions are prograde, in accordance with our initial hypothesis. In studying the long-term evolution of Eulalia’s spin state, we show that the obliquity can oscillate over a large interval of values yet always remain <90°. We estimate that Eulalia could have migrated by as much as ~0.007 au toward the J3/1 resonance within the past 1 Gyr. Our numerical runs show that it could have originated in the orbital zone well aligned with other family members in proper eccentricity, whichafter it gained its current orbit by chaotic evolution along the J3/1 resonance