► (8567) 1996 HW1 is a contact binary near-Earth asteroid. ► (8567) 1996 HW1 is a highly elongated near-Earth asteroid. ► (8567) 1996 HW1 could have originated as a binary asteroid system.
We ...observed near-Earth Asteroid (8567) 1996 HW1 at the Arecibo Observatory on six dates in September 2008, obtaining radar images and spectra. By combining these data with an extensive set of new lightcurves taken during 2008–2009 and with previously published lightcurves from 2005, we were able to reconstruct the object’s shape and spin state. 1996 HW1 is an elongated, bifurcated object with maximum diameters of 3.8
×
1.6
×
1.5
km and a contact-binary shape. It is the most bifurcated near-Earth asteroid yet studied and one of the most elongated as well. The sidereal rotation period is 8.76243
±
0.00004
h and the pole direction is within 5° of ecliptic longitude and latitude (281°, −31°). Radar astrometry has reduced the orbital element uncertainties by 27% relative to the
a priori orbit solution that was based on a half-century of optical data. Simple dynamical arguments are used to demonstrate that this asteroid could have originated as a binary system that tidally decayed and merged.
We carried out new photometric observations of asteroid (106) Dione at three apparitions (2004, 2012 and 2015) to understand its basic physical properties. Based on a new brightness model, new ...photometric observational data and published data of (106) Dione were analyzed to characterize the morphology of Dione's photometric phase curve. In this brightness model, a cellinoid ellipsoid shape and three-parameter (H,G1,G2) magnitude phase function system were involved. Such a model can not only solve the phase function system parameters of (106) Dione by considering an asymmetric shape of an asteroid, but also can be applied to more asteroids, especially those without enough photometric data to solve the convex shape. Using a Markov Chain Monte Carlo (MCMC) method, Dione's absolute magnitude of H=7.66−0.03+0.03 mag, and phase function parameters G1=0.682−0.077+0.077 and G2=0.081−0.042+0.042 were obtained. Simultaneously, Dione's simplistic shape, orientation of pole and rotation period were also determined preliminarily.
Arecibo (2380 MHz, 13 cm) radar observations of 2005 CR37 provide detailed images of a candidate contact binary: a 1.8-km-long, extremely bifurcated object. Although the asteroid's two lobes are ...round, there are regions of modest topographic relief, such as an elevated, 200-m-wide facet, that suggest that the lobes are geologically more complex than either coherent fragments or homogeneous rubble piles. Since January 1999, about 9% of NEAs larger than ∼200 m imaged by radar can be described as candidate contact binaries.
We report the results of an observational survey of rotation lightcurves for members of the Koronis asteroid family that we conducted using CCD imaging cameras at seven different observatories during ...the period 1998–2005. A total of 375 individual lightcurves yield new or refined rotation periods for the 24 survey objects (658) Asteria, (761) Brendelia, (811) Nauheima, (975) Perseverantia, (1029) La Plata, (1079) Mimosa, (1100) Arnica, (1245) Calvinia, (1336) Zeelandia, (1350) Rosselia, (1423) Jose, (1482) Sebastiana, (1618) Dawn, (1635) Bohrmann, (1725) CrAO, (1741) Giclas, (1742) Schaifers, (1848) Delvaux, (1955) McMath, (2123) Vltava, (2144) Marietta, (2224) Tucson, (2729) Urumqi, and (2985) Shakespeare. Most of the data have been calibrated to standard magnitudes. Several previously unpublished lightcurves recorded using a photoelectric photometer during the period 1987–1989 are also reported here. We present composite lightcurves and report derived synodic rotation periods. For those objects with sufficient coverage in solar phase angle we also determined Lumme–Bowell solar phase parameters, and for four objects we obtained
V
–
R
colors. Our results reduce selection biases among known rotation lightcurve parameters for Koronis family members by completing the sample down to
H
≈
11.2
, and they lay the foundation for future spin vector and shape determinations. The distribution of rotation rates in the available sample of
N
=
40
Koronis members is non-Maxwellian at a confidence level of 99%. It also seems to be qualitatively consistent with the effects of long-term modification by thermal YORP torques, as proposed by Vokrouhlický et al. Vokrouhlický, D., Nesvorný, D., Bottke, W.F., 2003. Nature 425, 147–151 to explain the distribution of the ten Koronis member spin vectors that have already been determined Slivan, S.M., 2002. Nature 419, 49–51; Slivan, S.M., Binzel, R.P., Crespo da Silva, L.D., Kaasalainen, M., Lyndaker, M.M., Krčo, M., 2003. Icarus 162, 285–307.
Asteroid pairs: A complex picture Pravec, P.; Fatka, P.; Vokrouhlický, D. ...
Icarus (New York, N.Y. 1962),
11/2019, Letnik:
333
Journal Article
Recenzirano
We studied a sample of 93 asteroid pairs, i.e., pairs of genetically related asteroids that are on highly similar heliocentric orbits. We estimated times elapsed since separation of pair members ...(i.e., pair age) that are between 7 × 103 yr and a few 106 yr. With photometric observations, we derived the rotation periods P1 for all the primaries (i.e., the larger members of asteroid pairs) and a sample of secondaries (the smaller pair members). We derived the absolute magnitude differences of the studied asteroid pairs that provide their mass ratios q. For a part of the studied pairs, we refined their WISE geometric albedos and collected or estimated their taxonomic classifications. For 17 asteroid pairs, we also determined their pole positions. In two pairs where we obtained the spin poles for both pair components, we saw the same sense of rotation for both components and constrained the angles between their original spin vectors at the time of their separation. We found that the primaries of 13 asteroid pairs in our sample are actually binary or triple systems, i.e., they have one or two bound, orbiting secondaries (satellites). As a by-product, we found also 3 new young asteroid clusters (each of them consisting of three known asteroids on highly similar heliocentric orbits). We compared the obtained asteroid pair data with theoretical predictions and discussed their implications. We found that 86 of the 93 studied asteroid pairs follow the trend of primary rotation period vs mass ratio that was found by Pravec et al. (2010). Of the 7 outliers, 3 appear insignificant (may be due to our uncertain or incomplete knowledge of the three pairs), but 4 are high mass ratio pairs that were unpredicted by the theory of asteroid pair formation by rotational fission. We discuss a (remotely) possible way that they could be created by rotational fission of flattened parent bodies followed by re-shaping of the formed components. The 13 asteroid pairs with binary primaries are particularly interesting systems that place important constraints on formation and evolution of asteroid pairs. We present two hypotheses for their formation: The asteroid pairs having both bound and unbound secondaries could be “failed asteroid clusters”, or they could be formed by a cascade primary spin fission process. Further studies are needed to reveal which of these two hypotheses for formation of the paired binary systems is real.
Pairs of asteroids sharing similar heliocentric orbits, but not bound together, were found recently. Backward integrations of their orbits indicated that they separated gently with low relative ...velocities, but did not provide additional insight into their formation mechanism. A previously hypothesized rotational fission process may explain their formation-critical predictions are that the mass ratios are less than about 0.2 and, as the mass ratio approaches this upper limit, the spin period of the larger body becomes long. Here we report photometric observations of a sample of asteroid pairs, revealing that the primaries of pairs with mass ratios much less than 0.2 rotate rapidly, near their critical fission frequency. As the mass ratio approaches 0.2, the primary period grows long. This occurs as the total energy of the system approaches zero, requiring the asteroid pair to extract an increasing fraction of energy from the primary's spin in order to escape. We do not find asteroid pairs with mass ratios larger than 0.2. Rotationally fissioned systems beyond this limit have insufficient energy to disrupt. We conclude that asteroid pairs are formed by the rotational fission of a parent asteroid into a proto-binary system, which subsequently disrupts under its own internal system dynamics soon after formation.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Basaltic V-type asteroids are common in the inner part of the Main Asteroid Belt and much less abundant in the mid and outer parts. They are of scientific interest because they sample crusts and ...mantles of theoretically plentiful differentiated planetesimals that existed in the Solar System four billion years ago. Some Solar System theories suggest that those objects formed in the terrestrial planet region and were then implanted in the main asteroid belt. In consequence, we should observe a large number of fragments of multiple differentiated planetesimals in the inner Main Belt. That region of the Asteroid Belt is filled with V-type fragments; however, they are difficult to tell apart from typical Vestoids and Vesta fugitives. In this work, we focus on physical and dynamical characterization of V-types in the inner Main-Belt and aim to reconcile those properties with the planetesimal formation and evolution theories.
We conducted an observing campaign over the years 2013–2022 and obtained photometric observations of V-type asteroids located mostly outside the Vesta family at specific locations of the inner Main Belt (the so-called Cells I and II). The total number of partial dense photometric lightcurves obtained in this study was ∼ 2910. We were able to model ∼100 V-types. We further supplement those data with 133 spins of V-types from the DAMIT database and 237 objects derived from Gaia DR3 (Ďurech & Hanuš 2023). We found 78%±11% and 38%±13% retrograde rotators in Cell I and II, respectively. This statistic is remarkably consistent with the numerical simulations of the escape paths of Vesta fugitives that predict 81% retrograde rotators in Cell I and 40% in Cell II after the dynamical integration of 2 Gys. Based on our statistics we conclude that if there are non-Vestoids in the inner main belt, they are likely to be very few. This is consistent with the small fraction of anomalous HED meteorites in meteorite collections, small number of non-Vestoids in the middle and outer Main Belt and points to planetesimal formation location close to the Sun.
•We determine spin and shape models for over ∼100 V-type asteroids.•We determine the observable statistics for sense of rotation for V-types in the inner main belt.•We verify the dynamical migration model of Nesvorny et al. 2008.
The existence of asteroid pairs, two bodies on similar heliocentric orbits, reveals an ongoing process of rotational fission among asteroids. This newly found class of objects has not been studied in ...detail yet. Here we choose asteroids (6070) Rheinland and (54827) 2001 NQ8, the most suitable pair for an in-depth analysis. First, we use available optical photometry to determine their rotational state and convex shapes. Rotational pole of Rheinland is very near the south ecliptic pole with a latitude uncertainty of about 10°. There are two equivalent solutions for the pole of 2001 NQ8, either (72°, −49°) or (242°, −46°) (ecliptic longitude and latitude). In both cases, the longitude values have about 10° uncertainty and the latitude values have about 15° uncertainty (both uncertainties). The sidereal rotation period of 2001 NQ8 is 5.877186 0.000002 hr. Second, we construct a precise numerical integrator to determine the past state vectors of the pair's components, namely their heliocentric positions and velocities, and orientation of their spin vectors. Using this new tool, we investigate the origin of the (6070) Rheinland and (54827) 2001 NQ8 pair. We find a formal age solution of 16.34 0.04 kyr. This includes effects of the most massive objects in the asteroid belt (Ceres, Pallas, and Vesta), but the unaccounted gravitational perturbations from other asteroids may imply that the realistic age uncertainty is slightly larger than its formal value. Analyzing results from our numerical simulation to 250 kya, we argue against a possibility that this pair would allow an older age. Initial spin vectors of the two asteroids, at the moment of their separation, were not collinear, but tilted by .
ABSTRACT The Schulhof family, a tight cluster of small asteroids around the central main belt body (2384) Schulhof, belongs to a so far rare class of very young families (estimated ages less than 1 ...Myr). Characterization of these asteroid clusters may provide important insights into the physics of the catastrophic disruption of their parent body. The case of the Schulhof family has been up to now complicated by the existence of two proposed epochs of its origin. In this paper, we first use our own photometric observations, as well as archival data, to determine the rotation rate and spin axis orientation of the largest fragment (2384) Schulhof. Our data also allow us to better constrain the absolute magnitude of this asteroid, and thus also improve the determination of its geometric albedo. Next, using the up-to-date catalog of asteroid orbits, we perform a new search of smaller members in the Schulhof family, increasing their number by 50%. Finally, the available data are used to access Schulhof's family age anew. We now find that the younger of the previously proposed two ages of this family is not correct, resulting from a large orbital uncertainty of single-opposition members. Our new runs reveal a single age solution of about 800 kyr with a realistic uncertainty of 200 kyr.
A radar survey of M- and X-class asteroids Shepard, Michael K.; Clark, Beth Ellen; Nolan, Michael C. ...
Icarus (New York, N.Y. 1962),
05/2008, Letnik:
195, Številka:
1
Journal Article
Recenzirano
We observed ten M- and X-class main-belt asteroids with the Arecibo Observatory's S-band (12.6 cm) radar. The X-class asteroids were targeted based on their albedos or other properties which ...suggested they might be M-class. This work brings the total number of main-belt M-class asteroids observed with radar to 14. We find that three of these asteroids have rotation rates significantly different from what was previously reported. Based on their high radar albedo, we find that only four of the fourteen—16 Psyche, 216 Kleopatra, 758 Mancunia, and 785 Zwetana—are almost certainly metallic. 129 Antigone has a moderately high radar albedo and we suggest it may be a CH/CB/Bencubbinite parent body. Three other asteroids, 97 Klotho, 224 Oceana, and 796 Sarita have radar albedos significantly higher than the average main belt asteroid and we cannot rule out a significant metal content for them. Five of our target asteroids, 16 Psyche, 129 Antigone, 135 Hertha, 758 Mancunia, and 785 Zwetana, show variations in their radar albedo with rotation. We can rule out shape and composition in most cases, leaving variations in thickness, porosity, or surface roughness of the regolith to be the most likely causes. With the exception of 129 Antigone, we find no hydrated M-class asteroids (W-class; Rivkin, A.S., Howell, E.S., Lebofsky, L.A., Clark, B.E., Britt, D.T., 2000. Icarus 145, 351–368) to have high radar albedos.
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