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 vector and shape of (6070) Rheinland and their implications

Main belt asteroids (6070) Rheinland and (54827) 2001NQ8 belong to a small population of couples of bodies which reside on very similar heliocentric orbits. Vokrouhlicky & Nesvorny (2008, AJ 136, 280) promoted a term "asteroid pairs", pointing out their common origin within the past tens to hundreds of ky. Previous attempts to reconstruct the initial configuration of Rheinland and 2001NQ8 at the time of their separation have led to the prediction that Rheinland's rotation should be retrograde. Here we report extensive photometric observations of this asteroid and use the lightcurve inversion technique to directly determine its rotation state and shape. We confirm the retrograde sense of rotation of Rheinland, with obliquity value constrained to be >= 140 deg. The ecliptic longitude of the pole position is not well constrained as yet. The asymmetric behavior of Rheinland's lightcurve reflects a sharp, near-planar edge in our convex shape representation of this asteroid. Our calibrated observations in the red filter also allow us to determine $H_R = 13.68\pm 0.05$ and $G = 0.31\pm 0.05$ values of the H-G system. With the characteristic color index $V-R = 0.49\pm 0.05$ for the S-type asteroids, we thus obtain $H = 14.17\pm 0.07$ for the absolute magnitude of (6070) Rheinland. This a significantly larger value than previously obtained from analysis of the astrometric survey observations. We next use the obliquity constraint for Rheinland to eliminate some degree of uncertainty in the past propagation of its orbit. This is because the sign of the past secular change of its semimajor axis due to the Yarkovsky effect is now constrained. Determination of the rotation state of the secondary component, asteroid (54827) 2001NQ8, is the key element in further constraining the age of the pair and its formation process.Comment: Published in AJ, 28 pages, 4 figures, 2 table

Asteroid candidates for mass determination

The first 9511 numbered asteroids are studied in terms of their mutual closest approaches and encounter velocities during the period from November 6, 1967, to September 13, 2023. Several large asteroids (diameter $200 \mathrm{km}$ and above) were (will be) encountered by smaller counterparts within a distance of $0.0200 \mathrm{AU}$. Thus, they are possible candidates for mass determination by the astrometrical method. Similarly, the search for effective perturbers is extended to even smaller asteroids for the much closer separation distance of $0.0020 \mathrm{AU}$ and below. Only the simplified method for evaluation of observable effects on a perturbed body is used. Asteroid masses alone are not computed here. But a stronger criterion to reveal pairs for this purpose in comparison to some specially devoted papers should compensate for the difference and act as a reliable test. The best candidates for mass determination at present are asteroids (1), (2), (4), (10), (11), (24), (52) and (65). This list may be extended by at least (29) in the next 5 years and by many others in the next two decades. Several other strong perturbers from the last three decades are not included in the list, while there is still only a limited number of (or no) precise and reliable observations of perturbed asteroids before a close encounter. It seems that a perturbation by (10) is at least as effective as that by (2) and could be included in asteroid orbit determination in the future. Except for their bulk density determinations (knowing the size), the masses of perturbers could occasionally be used to improve the precision of the computed orbit for perturbed large-numbered and unnumbered asteroids as well

Accuracy of calibrated data from the SDSS moving object catalog, absolute magnitudes, and probable lightcurves for several asteroids

It would seem that the calibrated observations obtained by the Sloan Digital Sky Survey (SDSS) by themselves would be, at best, marginally useful for the secure determination of asteroid rotation lightcurves, mostly due to the scarcity of data for a particular object in a given apparition as well as because of the sometimes low photometric quality of the SDSS data. Despite these shortcomings, it was decided to see if the SDSS data could be used to help find the lightcurve parameters of at least some asteroids. Observations of ten asteroids obtained by the SDSS are compared here with lightcurves obtained by asteroid photometric stations using dense data sets. Three asteroids observed during the same apparition as the SDSS observations served to determine the accuracy of the SDSS data. Except for occasional outliers identified on the basis of deviating color indices, the accuracy of the observations was found to be about 0.03 mag in the V band on average, which is a generally accepted level of quality for most asteroid photometry.
In addition to the ten asteroids with known lightcurves, another 54 asteroids without known lightcurves, but with more than 20 observations by SDSS, were also examined to derive their absolute magnitudes (H) and plausible composite lightcurves. Lightcurve analyses of (12104) Chesley, (32257) 2000 OW52, (39132) 2000 WU58, (156751) 2002 XL92, (219686) 2001 WE37, 1992 WW6, and 2007 EP39 are presented. The asteroids studied in this paper were found to be mostly fainter than predicted from the H values given by the Minor Planet Center in its Orbit Database. The difference between the H values slightly correlates with the lightcurve amplitude

Effect of main belt perturbers on asteroid-pair age estimation

Context. Asteroid-pair age estimations are usually performed by backward integration of possible orbits of pair components, taking planetary perturbations into account along with the Yarkovsky effect. It is assumed that uncertainties coming from the backward integration process itself are small, so to reduce uncertainties in estimations, effort usually focuses on reducing uncertainties in the initial orbital elements and the dimensions of the pair components. Aims. This work aims to evaluate the role of the frequently ignored nonplanetary perturbers in asteroid-pair age estimation. When their role is not negligible, the ages of the youngest known pairs can be roughly re-estimated. Methods. The orbital evolution of several asteroid-pair components and the close approaches between components during the last ≈43 kyr are investigated. Initially, the force equations consisted of only planetary perturbers. The three largest main belt perturbers were added afterwards. Finally, as many as 262 massive main belt perturbers were included. The effect of main belters on age estimation is assessed by comparing the dates of the closest approaches between pair components. The range of the Yarkovsky effect is simulated very roughly, only for comparison purposes. Results. The estimated age of the youngest known pair (6070) Rheinland – (54827) 2001 NQ8 including the Yarkovsky effect seems to be either 16.3 ± 0.1 kyr for the retrograde rotation or 16.0 ± 0.2 kyr for the prograde rotation of the second component, respectively. This is younger by about 0.7−0.9 kyr than the previous estimate. Several more pairs, namely (88259) 2001 HJ7 − 1999 VA117, (111962) 2002 GP75 − (280008) 2001 UR224, (180906) 2005 KB6 − (217266) 2003 YR67, (229401) 2005 SU152 − 2005 UY97, and 2005 GS180 − 2008 FK107, had relative encounter velocities within 1.0 m s-1, suggesting they might also have formed within the interval studied. Some other pairs, including (5026) Martes – 2005 WW113, which was previously reported as very young, had slightly higher encounter velocities and longer nominal minimum distances, calling into question whether they could have formed within the interval studied or in some previous mutual encounter of pair components. Conclusions. The effect of main belt perturbers on asteroid-pair age estimation is buried in the huge age uncertainties caused by the Yarkovsky effect until the rotation direction of pair components is recognized

Asteroid encounters suitable for mass determinations

As in a previous paper (Galád [CITE]), the search for effective perturbers among asteroids is done using the same method and during the same time period. The only difference is in the number of asteroids that were processed – 24 599 instead of 9511. Special attention is paid to comparison between perturbations due to (2) Pallas and (10) Hygiea. It is confirmed that the latter has a larger effect on the motion of main belt asteroids, perhaps by a factor of three. This is a reason to include its mass in asteroid orbit determinations.
In addition to the Big Four main belt asteroids – (1) Ceres, (2) Pallas, (4) Vesta, (10) Hygiea – the masses of many other large asteroids, such as (11) Parthenope, (13) Egeria, (15) Eunomia, (16) Psyche, (24) Themis, (29) , (39) Laetitia, (45) Eugenia, (52) Europa, (65) , (121) Hermione, (451) Patientia, and (511) Davida, could be achieved by the end of this decade using astrometric data. In general, over the next decade small asteroids (with much higher numbers than above) will be used more thoroughly for mass determination of large asteroids

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

Photometry of 2004 RZ164: a probable binary asteroid

Aims.We observed a near-Earth asteroid 2004 RZ164 to study its rotational properties. The object was chosen because of its small diameter of about 700 m, which is close to the 150 m threshold, separating monolithic and rubble-pile asteroids. Methods.With small telescopes at five observatories, equipped with CCD cameras, we obtained seven lightcurves, which were taken through the clear, R, and I filters. Results.Despite significant changes in the observing geometries (and large phase angles during observations), the peak-to-peak amplitudes of the lightcurves never exceeded 0\fm15, suggesting the almost spheroidal shape of this asteroid. There is a signature of a probable occultation/eclipse event in one of the lightcurves, which suggests 2004 RZ164 is a binary asteroid. Its primary component spins with a period of P=2\fh5559\pm 0\fh0001 and the orbital period of the system is longer than 10\fh8