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Figure of the double Asteroid 90 Antiope from adaptive optics and lightcurve observations
Abstract
A long-term adaptive optics (AO) campaign of observing the double Asteroid (90) Antiope has been carried out in 2003–2005 using 8–10-m class telescopes, allowing prediction of the circumstances of mutual events occurring during the July 2005 opposition [Marchis, F., Descamps, P., Hestroffer, D., Berthier, J., de Pater, I., 2004. Bull. Am. Astron. Soc. 36, 1180]. This is the first opportunity to use complementary lightcurve and AO observations to extensively study the (90) Antiope system, an interesting visualized binary doublet system located in the main belt. The orbital parameters derived from the AO observations have served as input quantities for the derivation of a whole set of other physical parameters (namely shapes, surface scattering, bulk density, and internal properties) from analysis of collected lightcurves. To completely model the observed lightcurves, we employed Roche figures to construct an overall shape solution. The combination of these complementary observations has enabled us to derive a reliable physical and orbital solution for the system. Our model is consistent with a system of slightly non-spherical components, having a size ratio of 0.95 (with Ravg=42.9±0.5 km, separation=171±1 km), and exhibiting equilibrium figures for homogeneous rotating bodies. A comparison with grazing occultation event lightcurves suggests that the real shapes of the components do not depart from Roche equilibrium figures by more than 10%. The J2000 ecliptic coordinates of the pole of the system are λn=200°±2° and αn=38°±2°. The orbital period was refined to P=16.5051±0.0001 h, and the density is found to be slightly lower than previous determinations, with a value of 1.25±0.05 g/cm3, leading to a significant macro-porosity of 30%. Possible scenarios for the origin of the system are also discussed.
... Note that in this way we obtain a model very close to reality and the dependence of the accuracy of the ephemeris on the observation's time interval is shown here directly. Descamps et al. (2007) and in the present paper. The orbit's inclination, the longitude of the ascending node and the pericentre argument ω refer to the Earth's equator (J2000). ...
... Parameter Descamps et al. (2007) The covariance matrices of the parameters required for the proposed calculations for all 62 moons are given in Table S4. A complete report on the accuracy of the ephemerides obtained for all 62 moons using the proposed method will be the subject of our next paper. ...
... The orbit of the moon S/2000(90)1 of the asteroid (90) Antiope was determined in Descamps et al. (2007) based on the same observations as in our paper. The orbital parameters of this asteroid moon determined in Descamps et al. and in the present paper are given in Table 1 for comparison. ...
Based on all published astrometric observations, we have determined the moon orbits for asteroids using a model of the fixed Keplerian orbit. We applied 5–114 observations for each moon. As a result, we have determined the orbits of 62 moons. All results, including the orbital parameters obtained, are presented in the tables that are provided as supplementary material, available online. These data can be used to calculate the ephemerides of the moons of the asteroids. Among the moons considered, 13 belong to asteroids of the main asteroid belt, two are the moons of Jupiter Trojan asteroids, while the rest are trans-Neptunian objects. Our results are in good agreement with the corresponding results published in the literature. We argue that reliable estimates of the accuracy for the ephemerides can be only made using parameter covariance matrices. These matrices that we have obtained are also given in the supporting information.
... The conditions explained above are then applied to the irregular synchronous asteroid systems (3169) Ostro 15-17 and (90) Antiope 18,19 . The variations of the parameters 0 and 0 allow us to obtain different anchor positions for the tether, including positions outside the orbital plane of the primaries. ...
... Another effect of the irregular shape of the bodies is that the original family coming from the spherical model is modified. Figures 17,18,19 and 20 show the out of plane equilibrium solutions for the spacecraft considering 0 ≤ ≤ 2 , assuming different points for the location of the anchor in the reference plane ( 0 = 0). There are no out of plane solutions for the situations with the anchor in the plane of the primaries, when irregular bodies are considered. ...
Several new applications of space tethers to maneuver spacecrafts have been suggested recently. Some of them are combinations with the sling shot effect used in several interplanetary missions. In one type of this family of applications, the tether is attached to an asteroid to make a rotation of the spacecraft, so giving energy to send it to the exterior planets of the Solar System or beyond. A similar idea is to make the capture of spacecrafts by a planet of the Solar System using tethers fixed on their moons. In both of these proposals, the tether is car-ried on-board the spacecraft and anchored to the celestial body during the approach phase. Another possibility is to build an "Escape Portal" using a tether permanently fixed in an asteroid to give energy to spacecrafts to go to the outer planets. The present paper explores in more detail a combination of those two proposals to build a "Capture Portal" for the planets. The main idea is to build a permanent structure fixed on one of the moons of a given planet, so that it can be used for an unlimited number of maneuvers. With this goal, this research searches for equilibrium points that can be used to place the above structures. The type of force in the tether and the stability of the points are also considered. The results shown here can give some insights in the problems that appear when building such “Capture Portal”
... The conditions explained above are then applied to the irregular synchronous asteroid systems (3169) Ostro 15-17 and (90) Antiope 18,19 . The variations of the parameters 0 and 0 allow us to obtain different anchor positions for the tether, including positions outside the orbital plane of the primaries. ...
... Another effect of the irregular shape of the bodies is that the original family coming from the spherical model is modified. Figures 17,18,19 and 20 show the out of plane equilibrium solutions for the spacecraft considering 0 ≤ ≤ 2 , assuming different points for the location of the anchor in the reference plane ( 0 = 0). There are no out of plane solutions for the situations with the anchor in the plane of the primaries, when irregular bodies are considered. ...
... -The density values recorded for two family members (90 Antiope and 379 Huenna: ¡1.3 g/cm 3 ; Descamps et al. 2007; Marchis et al. 2008) are among the lowest densities measured so far for large (D¿100 km) main-belt asteroids, very likely implying a high fraction of ice(s) in the interior of these bodies (see discussion on the porosity and ice/rock composition of 90 Antiope in Castillo-Rogez & Schmidt 2010). ...
... -The density values recorded so far for two family members (90 Antiope and 379 Huenna: ¡1.3 g/cm 3 ; Descamps et al. 2007;Marchis et al. 2008) likely imply a large amount of ice(s) in the interior of these bodies. ...
Context. It has recently been proposed that the surface composition of icy
main-belt asteroids (B-,C-,Cb-,Cg-,P-,and D-types) may be consistent with that
of chondritic porous interplanetary dust particles (CPIDPs). Aims. In the light
of this new association, we re-examine the surface composition of a sample of
asteroids belonging to the Themis family in order to place new constraints on
the formation and evolution of its parent body. Methods. We acquired NIR
spectral data for 15 members of the Themis family and complemented this dataset
with existing spectra in the visible and mid-infrared ranges to perform a
thorough analysis of the composition of the family. Assuming end-member
minerals and particle sizes (<2\mum) similar to those found in CPIDPs, we used
a radiative transfer code adapted for light scattering by small particles to
model the spectral properties of these asteroids. Results. Our best-matching
models indicate that most objects in our sample possess a surface composition
that is consistent with the composition of CP IDPs.We find ultra-fine grained
Fe-bearing olivine glasses to be among the dominant constituents. We further
detect the presence of minor fractions of Mg-rich crystalline silicates. The
few unsuccessfully matched asteroids may indicate the presence of interlopers
in the family or objects sampling a distinct compositional layer of the parent
body. Conclusions. The composition inferred for the Themis family members
suggests that the parent body accreted from a mixture of ice and anhydrous
silicates (mainly amorphous) and subsequently underwent limited heating. By
comparison with existing thermal models that assume a 400km diameter
progenitor, the accretion process of the Themis parent body must have occurred
relatively late (>4Myr after CAIs) so that only moderate internal heating
occurred in its interior, preventing aqueous alteration of the outer shell.
... , σ 2 μ 343 ) for 343 asteroid mass parameters is determined in the following way. For mass parameters obtained by tracking the motions of a spacecraft encountering an asteroid (Miller et al. 2002;Konopliv et al. 2014Konopliv et al. , 2018Pätzold et al. 2011), by observations of asteroid satellites for binary asteroids (Marchis et al. 2005;Descamps et al. 2007;Descamps et al. 2009;Rojo and Margot 2011;Descamps et al. 2011;Marchis et al. 2013;Carry et al. 2019), and by measuring orbit perturbation by mutual gravitational interaction between asteroids (Kochetova 2004;Baer et al. 2011;Baer and Chesley 2017), their uncertainties taken from the references are adopted without any scaling. ...
The aim of this work is to develop a new numerical ephemeris of the Sun, the eight planets, the Pluto and the Moon. We first construct a dynamical model, which consists of translational equations of motion for the major bodies and 343 asteroids and of rotational equations of motion for a two-layered Moon. By aligning initial state parameters of the considered bodies and physical parameters in the dynamical model to the JPL ephemeris DE430, we evaluated the adopted dynamical model through a detailed comparison with DE430. After the test, a weighted least square method is applied to fit ephemeris parameters to planetary and lunar observations from 1925 to 2021 simultaneously, and an initial version of our planetary and lunar ephemeris PETREL19 is built. Mass parameters of the 343 asteroids are determined along with other ephemeris parameters by an iteration procedure.
... Over the past 40 years, occultation have been used to derive the size, shape, and multiplicity of asteroids. Combined with other techniques such as radar detection (Ostro et al. 2000), direct imaging by adaptive optics on ground-based telescopes (Descamps et al. 2007 andVernazza et al. 2021) or using the Hubble Space Telescope (Parker et al. 2006)), astronomers can gain new insights into asteroids. Unfortunately because only a handful number of space missions have flown past asteroids (Barucci et al. 2007), and even fewer have orbited them (Russell & Raymond 2011), today our knowledge about these asteroids relies mostly on remote observing methods. ...
We propose to design and build an algorithm that will use a convolutional neural network (CNN) and observations from the Unistellar Network to reliably detect asteroid occultations. The Unistellar Network is made of more than 10,000 digital telescopes owned by citizen scientists, and is regularly used to record asteroid occultations. In order to process the increasing amount of observational produced by this network, we need a quick and reliable way to analyze occultations. In an effort to solve this problem, we trained a CNN with artificial images of stars with 20 different types of photometric signals. Inputs to the network consist of two stacks of snippet images of stars, one around the star that is supposed to be occulted and a reference star used for comparison. We need the reference star to distinguish between a true occultation and artifacts introduced by a poor atmospheric condition. Our Occultation Detection Neural Network can analyze three sequences of stars per second with 91% precision and 87% recall. The algorithm is sufficiently fast and robust so we can envision incorporating it on board the eVscopes to deliver real-time results. We conclude that citizen science represents an important opportunity for the future studies and discoveries in the occultations, and that application of artificial intelligence will permit us to to take better advantage of the ever-growing quantity of data to categorize asteroids.
... Over the past forty years, occultation have been used to derive the size, shape, and multiplicity of asteroids. Combined with other techniques such as radar detection (Ostro et al. (2000)), direct imaging by adaptive optics on ground-based telescopes (Descamps et al. (2007) and Vernazza et al. (2021)) or using the Hubble Space Telescope (Parker et al. 2006)), astronomers can gain new insights into asteroids. Unfortunately because only a handful number of space missions have flown past asteroids (Barucci et al. 2007), and even fewer have orbited them (Russell & Raymond 2011), today our knowledge about these asteroids relies mostly on remote observing methods. ...
We propose to design and build an algorithm that will use a Convolutional Neural Network (CNN) and observations from the Unistellar network to reliably detect asteroid occultations. The Unistellar Network, made of more than 10,000 digital telescopes owned by citizen scientists, and is regularly used to record asteroid occultations. In order to process the increasing amount of observational produced by this network, we need a quick and reliable way to analyze occultations. In an effort to solve this problem, we trained a CNN with artificial images of stars with twenty different types of photometric signals. Inputs to the network consists of two stacks of snippet images of stars, one around the star that is supposed to be occulted and a reference star used for comparison. We need the reference star to distinguish between a true occultation and artefacts introduced by poor atmospheric condition. Our Occultation Detection Neural Network (ODNet), can analyze three sequence of stars per second with 91\% of precision and 87\% of recall. The algorithm is sufficiently fast and robust so we can envision incorporating onboard the eVscopes to deliver real-time results. We conclude that citizen science represents an important opportunity for the future studies and discoveries in the occultations, and that application of artificial intelligence will permit us to to take better advantage of the ever-growing quantity of data to categorize asteroids.
... The origin of the (90) Antiope system is still not fully clear. Descamps et al. (2007) suggested that the system could have originated in a catastrophic collision in the Themis family probably during or just after the disruption of a 400-km parent asteroid about 2.5 Gyr ago. (90) Antiope is located in the outer asteroid belt, with a perihelion of 2.639 au and an aphelion distance of 3.670 au. ...
We provide a generalized discussion on the dynamics of a spacecraft around the equal-mass binary asteroid (90) Antiope, under the influence of solar radiation pressure at the perihelion and aphelion distances of the asteroid from the Sun. The polyhedral shape of the components of this asteroid is used to accurately model the gravitational field. Five unstable equilibrium points are determined and classified into two cases that allow classifying of the motion associated with the target as always unstable. The dynamical effects of the mass ratio of our binary system are investigated. We tested massless particles initially located at the periapsis distance on the equatorial plane of the primary of our binary asteroid. Bounded orbits around our system are not found for the longitudes λ ∈ {60, 90, 120, 240, 270, 300}. We also discuss the orbital dynamics in the full potential field of (90) Antiope. The tested motions are mainly dominated by the binary’s gravitational field; no significant effects of the SRP are detected. For λ = 180°, less perturbed orbits are identified between 420 and 700 km from the centre of the system, that corresponds to orbits with Δa < 30 km and Δe < 0.15. All the orbits with initial periapsis distance smaller than 350 km either collide with components of our asteroid or escape from the system.
... The critical period at ∼ 3h provides an estimate of the bulk density of 1.2 g/cm 3 . The bulk density of (24) Themis was estimated at 1.81 ± 0.67 g/cm 3 by Carry (2012), while Descamps et al. (2007) studied the binary asteroid (90) Antiope, a member of the Themis family, and found a density of 1.25±0.05 g/cm 3 . ...
Context. Asteroid families are witnesses to the intense collisional evolution that occurred on the asteroid belt. The study of the physical properties of family members can provide important information about the state of differentiation of the parent body and provide insights into how these objects were formed. Several of these asteroid families identified across the main belt are dominated by low-albedo, primitive asteroids. These objects are important for the study of Solar System formation because they were subject to weaker thermophysical processing and provide information about the early conditions of our planetary system.
Aims. We aim to study the diversity of physical properties among the Themis, Hygiea, Ursula, Veritas, and Lixiaohua families.
Methods. We present new spectroscopic data, combined with a comprehensive analysis using a variety of data available in the literature, such as albedo and rotational properties.
Results. Our results show that Themis and Hygiea families, the largest families in the region, present similar levels of hydration. Ursula and Lixiaohua families are redder in comparison to the others and present no sign of hydrated members based on the analysis of visible spectra. Conversely, Veritas presents the highest fraction of hydrated members.
Conclusions. This work demonstrates a diverse scenario in terms of the physical properties of primitive outer-belt families, which could be associated with dynamical mixing of asteroid populations and the level of differentiation of the parental body.
... Apart from the MBCs other asteroid members of the family were found to have both the "round" 3 µm water-ice band, such as (90) Antiope (Hargrove et al. 2015) and the "sharp" absorption such as (104) Klymene (Takir & Emery 2012), showing the presence of OH into the mineral lattice (Jones 1988). Additional evidence, that these objects could have high water content, comes from the densities of three Themis members, (24) Themis, (90) Antiope and (379) Huenna, that have very low density values, around 1,280-1,800 kg m 3 (Descamps et al. 2007;Carry 2012). Geophysical evolution models for (24) Themis (Castillo-Rogez & Schmidt 2010) have suggested that the parent body had accreted from ice mixed with carbonaceous material and before the time of the breakup -forming the Themis family -it differentiated, implying that more asteroids members of the family should contain water-ice. ...
Asteroid (16) Psyche, that for long was the largest M-type with no detection of hydration features in its spectrum, was recently discovered to have a weak 3 micron band and thus it eventually was added to the group of hydrated asteroids. Its relatively high density in combination with the high radar albedo, led to classify the asteroid as a metallic object, possibly a core of a differentiated body, remnant of "hit-and-run" collisions. The detection of hydration is, in principle, inconsistent with a pure metallic origin of this body. Here we consider the scenario that the hydration on its surface is exogenous and was delivered by hydrated impactors. We show that impacting asteroids that belong to families whose members have the 3 m band can deliver the hydrated material to Psyche. We developed a collisional model with which we test all the dark carbonaceous asteroid families, which contain hydrated members. We find that the major source of hydrated impactors is the family of Themis, with a total implanted mass on Psyche to be of the order of 10^14 kg. However, the hydrated fraction could be only a few per cent of the implanted mass, as the water content in carbonaceous chondrite meteorites, the best analogue for the Themis asteroid family, is typically a few per cent of their mass.
... Size and shape information can then be extracted directly. Direct, accurate measurements of asteroid physi- Kepler's 3 rd law; e.g., Merline et al. [2002]; Marchis et al. [2005]; Descamps et al. [2007]). ...
The combination of visible and thermal data from the ground and astrophysics space missions is key to improving the scientific understanding of near-Earth, main-belt, trojans, centaurs, and trans-Neptunian objects. To get full information on a small sample of selected bodies we combine different methods and techniques: lightcurve inversion, stellar occultations, thermophysical modeling, radiometric methods, radar ranging and adaptive optics imaging. The SBNAF project will derive size, spin and shape, thermal inertia, surface roughness, and in some cases bulk densities and even internal structure and composition, for objects out to the most distant regions in the Solar System. The applications to objects with ground-truth information allows us to advance the techniques beyond the current state-of-the-art and to assess the limitations of each method. We present results from our project's first phase: the analysis of combined Herschel-KeplerK2 data and Herschel-occultation data for TNOs; synergy studies on large MBAs from combined high-quality visual and thermal data; establishment of well-known asteroids as celestial calibrators for far-infrared, sub-millimetre, and millimetre projects; first results on near-Earth asteroids properties from combined lightcurve, radar and thermal measurements, as well as the Hayabusa-2 mission target characterisation. We also introduce public web-services and tools for studies of small bodies in general.
... Recently a new algorithm capable to generate model solutions for binary asteroids has been developed using a nonconvex shape representation of the components [1]. As the model is able to reproduce body concavities, the relative volume obtained for the components is more accurate than for the pre-vious models, which were based in Roche ellipsoids [11], having a direct impact on the density calculation. ...
Despite the large amount of high quality data generated in recent space encounters with asteroids, the majority of our knowledge about these objects comes from ground based observations. Asteroids travelling in orbits that are potentially hazardous for the Earth form an especially interesting group to be studied. In order to predict their orbital evolution, it is necessary to investigate their physical properties. This paper briefly describes the data requirements and different techniques used to solve the lightcurve inversion problem. Although photometry is the most abundant type of observational data, models of asteroids can be obtained using various data types and techniques. We describe the potential of radar imaging and stellar occultation timings to be combined with disk-integrated photometry in order to reveal information about physical properties of asteroids.
... Several articles are based on observations using various techniques namely radar (Ostro et al. 2002(Ostro et al. , 2000Magri et al. 2007), adaptive optics (Marchis et al. 2005), adaptive optics combined with lightcurve photometry (Descamps et al. 2007), and lightcurve photometry Pravec et al. 2002). ...
The fundamental goal of the planetary sciences is to understand the formation and evolution of the Solar System. For achieving this goal, the asteroids are of a special interest to the astronomical community as a possible window back to the beginning of the planetary formation. Being the only remnants of the early stages of planetary history they recorded the complex chemical and physical evolution that occurred in the solar nebula. Thus, the knowledge of both dynamical and physical properties of the current asteroid population brings valuable information for understanding the Solar System and more generally other planetary systems. In this thesis I present the project Modeling for Asteroids (acronym M4AST). M4AST is an on-line service that I developed for modeling surfaces of asteroids using several theoretical approaches. M4AST consists into a database containing more than 2,500 spectra of asteroids together with a library of routines which can model and extract several mineralogical parameters. The database M4AST could be accessed via its own webpage interface as well as via the Virtual Observatory (VO-Paris) protocols. This service is available to the web address http://cardamine.imcce.fr/m4ast. It allows several routines for modeling spectra: taxonomic classification, space weathering effects modeling, comparison to laboratory spectra of meteorites and minerals, band centers and band area computing. I have participated to more than 10 observational campaigns for observing both physical and orbital parameters of asteroids. The objective of spectral runs was to characterize the mineralogical properties of these bodies based on their reflectance spectra. Astrometry was mainly devoted to the confirmation and secures orbits of new discovered asteroid. During the thesis I observed and characterized near-infrared spectra of eight Near Earth Asteroids namely 1917, 8567, 16960, 164400, 188452, 2010 TD54, 5620, and 2001 SG286. These observations were obtained using the NASA telescope IRTF equipped with the spectroimager SpeX, and the CODAM-Paris observatory facilities. Based on these spectra mineralogical solutions were proposed for each asteroid. The taxonomic classification of five of these objects was reviewed and a corresponding type was assigned to the other three asteroids that were not classified before. Four of the observed objects have delta - V lower than 7 km/sec, which make them suitable targets in terms of propulsion for a future spacecraft mission. The asteroid (5620) Jasonwheeler exhibits spectral behaviors similar to the carbonaceous chondrite meteorites. I observed and modeled six Main Belt Asteroids. (9147) Kourakuen, (854) Frostia, (10484) Hecht and (31569) 1999 FL18 show the characteristics of V-type objects, while (1333) Cevenola, (3623) Chaplin belong to S-complex. Some of them have some peculiar properties: (854) Frostia is a binary asteroid, (10484) Hecht and (31569) 1999 FL18 have pairs, (1333) Cevenola, (3623) Chaplin show large amplitude lightcurves. The taxonomic classification, the comparisons to the meteorite spectra from the Relab database and the mineralogical analysis converged to the same solutions for each of these objects, allowing to find important details for the chemical compositions and resemblances to the Howardite-Eucrite-Diogenite class of meteorites.
... These are too large, with diameters greater than 100 km, to have gained angular momentum from thermal effects and collision simulations do not typically create such systems (Durda et al. 2004). They have very large angular momentum content, owing to the similar-sized components (Pravec and Harris 2007; Descamps et al. 2007; Michałowski et al. 2004). Antiope is notable as it is among the largest fragments in an asteroid family owing to the exceptional size of Themis and its family. ...
Satellites of asteroids have been discovered in nearly every known small body
population, and a remarkable aspect of the known satellites is the diversity of
their properties. They tell a story of vast differences in formation and
evolution mechanisms that act as a function of size, distance from the Sun, and
the properties of their nebular environment at the beginning of Solar System
history and their dynamical environment over the next 4.5 Gyr. The mere
existence of these systems provides a laboratory to study numerous types of
physical processes acting on asteroids and their dynamics provide a valuable
probe of their physical properties otherwise possible only with spacecraft.
Advances in understanding the formation and evolution of binary systems have
been assisted by: 1) the growing catalog of known systems, increasing from 33
to nearly 250 between the Merline et al. (2002) Asteroids III chapter and now,
2) the detailed study and long-term monitoring of individual systems such as
1999 KW4 and 1996 FG3, 3) the discovery of new binary system morphologies and
triple systems, 4) and the discovery of unbound systems that appear to be
end-states of binary dynamical evolutionary paths.
Specifically for small bodies (diameter smaller than 10 km), these
observations and discoveries have motivated theoretical work finding that
thermal forces can efficiently drive the rotational disruption of small
asteroids. Long-term monitoring has allowed studies to constrain the system's
dynamical evolution by the combination of tides, thermal forces and rigid body
physics. The outliers and split pairs have pushed the theoretical work to
explore a wide range of evolutionary end-states.
... For example, the Ida-Dactyl system is a large asteroid with a small companion (D p =D s ¼ 22:4, where D p and D s are the diameter of primary and satellite, respectively) with a small system semi-major axis that is only 3.44 D p (Belton et al., 1994(Belton et al., , 1995, while 90 Antiope is a large (D p = 87.80, Johnston, 2013) binary asteroid system with nearly equal size components (D p =D s ¼ 1:05) separated by 117 km (Merline et al., 2000;Descamps et al., 2007). In contrast to these larger systems, 1509 Esclangona is thought to be composed of two small asteroids (D s =D p ¼ 0:5) with D p ¼ 8:0 AE 0:8 km and D s ¼ 4 AE 0:7 km (Marchis et al., 2012). ...
... For DE430 and DE431, asteroid mass parameter estimates from other techniques were included as a priori constraints. Estimates were included based on close encounters between asteroids [90,91], masses of binary asteroids [92][93][94][95], and masses determined from radio tracking of spacecraft directly affected by the gravity of individual asteroids [96][97][98][99]. The mass parameters used for DE430/DE431 are given in Table 12. ...
The planetary and lunar ephemerides DE430 and DE431 are generated by fitting numerically integrated orbits of the Moon and planets to observations. The present-day lunar orbit is known to submeter accuracy through fitting lunar laser ranging data with an updated lunar gravity field from the Gravity Recovery and Interior Laboratory (GRAIL) mission. The orbits of the inner planets are known to subkilometer accuracy through fitting radio tracking measurements of spacecraft in orbit about them. Very long baseline interferometry measurements of spacecraft at Mars allow the orientation of the ephemeris to be tied to the International Celestial Reference Frame with an accuracy of 0''.0002. This orientation is the limiting error source for the orbits of the terrestrial planets, and corresponds to orbit uncertainties of a few hundred meters. The orbits of Jupiter and Saturn are determined to accuracies of tens of kilometers as a result of fitting spacecraft tracking data. The orbits of Uranus, Neptune, and Pluto are determined primarily from astrometric observations, for which measurement uncertainties due to the Earth's atmosphere, combined with star catalog uncertainties, limit position accuracies to several thousand kilometers. DE430 and DE431 differ in their integrated time span and lunar dynamical modeling. The dynamical model for DE430 included a damping term between the Moon's liquid core and solid mantle that gives the best fit to lunar laser ranging data but that is not suitable for backward integration of more than a few centuries. The ephemeris DE431 is similar to DE430 but was fit without the core/mantle damping term, so the lunar orbit is less accurate than in DE430 for times near the current epoch, but is more suitable for times more than a few centuries in the past. DE431 is a longer integration (covering years -13,200 to +17,191) than DE430 (covering years 1550 to 2650).
... The spin vector was derived from an iterative procedure based on the estimation of the epoch corresponding to a nearly perfect edge-on aspect of the system. This method was described carefuly in Descamps et al. (2007b). In the present case, we initially guessed that this epoch was around September−December 2005, given the high magnitude drops recorded in the lightcurves during this period of time. ...
CCD photometry of 809 Lundia obtained between September 2005 and January 2006 at Borowiec and Pic du Midi Observatories demonstrates that this object is a synchronous binary system with an orbital period of 15.418 ± 0.001 h. In this paper, we present the results of photometric observations of Lundia from two oppositions in 2005/2006 and 2007, as well as the first modelling of the system. For simplicity we assumed a fluid-like nature for each component with a modified Roche model and a triaxial ellipsoid shape in kinematic models. Our models provided similar results. Poles of the orbit in ecliptic coordinates are lambda = 119 ± 2°, beta = 28 ± 4° (modified Roche) or lambda = 120 ± 5°, beta = 18 ± 12° (kinematic). Triaxial ellipsoid shape solutions and a separation between components of 15.8 km are given after taking an equivalent diameter of 9.1 km from H = 11.8 mag and assuming an albedo of 0.4. The orbital period of the Lundia system obtained from modelling is the same as from the lightcurve analysis i.e., 15.418 ± 0.001 h. The bulk density of both components is 1.64 or 1.71 ± 0.01 g/cm^3. The double system of Lundia probably originates from the fission process of a single body that could have been spun up by the YORP effect. The predicted lightcurves for future oppositions are also presented.
... With this assumption, and with equilibrium shapes for fluid binaries obtained by invoking the ''Roche binary approximation " ofLeone et al. (1985), a binary system's ellipsoidal model is optimized by matching simulated light-curves with actual ones. This approach, christened as ''Roche formalism " by Descamps (2008), was followed byCellino et al. (1985)to provide shape models and density estimates of ten suspected binaries: 15Eunomia; 39 Laetitia; 43 Ariadne; 44 Nysa; 61 Danae; 63 Ausonia; 82 Alkeme; 192 Nausikaa; 216 Kleopatra; 624 Hektor.Recent investigations include several main belt binary systems: 3169 Ostro (Descamps et al., 2007a); 90 Antiope (Descamps et al., 2007b); 69230 Hermes, 617 Patroclus and 854 Frostia (Descamps, 2008); 216 Kleopatra (Takahashi et al., 2004), Trojan Asteroids: 624 Hektor (Lacerda and Jewitt, 2007;Mann et al., 2007); Asteroids (17365) and (29314) (Mann et al., 2007), and alsoFig. 13. ...
Binaries are in vogue; many minor-planets like asteroids are being found to be binary or contact-binary systems. Even ternaries like 87 Sylvia have been discovered. The densities of these binaries are often estimated to be very low, and this, along with suspected accretionary origins, hints at a rubble interior. As in the case of fluid objects, a rubble-pile is unable to sustain all manners of spin, self-gravitation, and tidal interactions. This motivates the present study of the possible ellipsoidal shapes and mutual separations that members of a rubble-pile binary system may achieve. Conversely, knowledge of a granular binary’s shape and separation will constrain its internal structure – the ability of the binary’s members to sustain elongated shapes and/or maintain contact will hint at appreciable internal frictional strength. Because the binary’s members are allowed to be of comparable mass, the present investigation constitutes an extension of the second classical Darwin problem to granular aggregates.
... Several articles are based on observations using various techniques, namely radar (Ostro et al. 2000(Ostro et al. , 2002Magri et al. 2007), adaptive optics (Marchis et al. 2005), adaptive optics combined with light-curve photometry (Descamps et al. 2007) and light-curve photometry (Pravec et al. 2002;Behrend et al. 2006). ...
Near-infrared spectroscopy can play a key role in establishing the mineralogical composition of objects and supporting other physical data obtained by complementary observational techniques such as adaptive optics, radar and photometry. The objective of our survey was asteroids that present large variations in their light curves. We report observations for asteroids (854) Frostia, (1333) Cevenola and (3623) Chaplin carried out in the 0.8–2.5 μm spectral range using SpeX/Infrared Telescope Facility (IRTF) in LowRes mode. The spectral modelling of these asteroids gives new insights into these peculiar objects in the main belt. (854) Frostia is a V-type asteroid, and its spectral properties are similar to those of basalts. The most probable mineralogical solution Wo8Fs43En49 was calculated for Frostia. (1333) Cevenola was estimated to have an Sq spectral type, in agreement with its membership of the Eunomia family. (3623) Chaplin is an S-type asteroid, in agreement with the taxonomic type of the Koronis family.
... We can now draw a convincing picture of Kleopatra's story, born from the aftermath of a reaccumulation process following the violent disruption of a parent body and sped up fast enough to deform according to the rough guidelines given by the equilibrium sequences of a spinning liquid mass. Such a scenario was already invoked to account for the way the synchronous double system of (90) Antiope, endowed with the same total specific angular momentum, was formed (Descamps et al., 2007Descamps et al., , 2009b). This does not mean that the interiors are liquid but only that the loosely packed internal structure may interact and react in a similar manner as a liquid mass does over a long period of time. ...
To take full advantage of the September 2008 opposition passage of the M-type Asteroid (216) Kleopatra, we have used near-infrared adaptive optics (AO) imaging with the W.M. Keck II telescope to capture unprecedented high resolution images of this unusual asteroid. Our AO observations with the W.M. Keck II telescope, combined with Spitzer/IRS spectroscopic observations and past stellar occultations, confirm the value of its IRAS radiometric radius of 67.5 km as well as its dog-bone shape suggested by earlier radar observations. Our Keck AO observations revealed the presence of two small satellites in orbit about Kleopatra (see Marchis, F. et al. [2008a]. (3749) Balam. In: Green, D.W.E. (Ed.), IAU Circ. 8928; Marchis, F., Descamps, P., Berthier, J., Emery, J.P. [2008b]. S/2008 ((216)) 1 and S/2008 ((216)) 2. In: Green, D.W.E. (Ed.), IAU Circ. 8980). Accurate measurements of the satellite orbits over a full month enabled us to determine the total mass of the system to be 4.64 ± 0.02 × 1018 kg. This translates into a bulk density of 3.6 ± 0.4 g/cm3, which implies a macroscopic porosity for Kleopatra of ∼30–50%, typical of a rubble-pile asteroid. From these physical characteristics we measured its specific angular momentum, very close to that of a spinning equilibrium dumbbell.Research highlights► In this study we observed and modelled the Asteroid (216) Kleopatra through different technics. ► The work revealed two moonlets orbiting Kleopatra. ► From these observations we derived the equivalent radius of Kleopatra and its macroscopic bulk density.
PRAIA – Package for the Reduction of Astronomical Images Automatically – is a suite of photometric and astrometric tasks designed to cope with huge amounts of heterogeneous observations with fast processing, no human intervention, minimum parametrization and yet maximum possible accuracy and precision. It is the main tool used to analyse astronomical observations by an international collaboration involving Brazilian,
French and Spanish researchers under the Lucky Star umbrella for Solar System studies. Here, we focus on the concepts of differential aperture photometry and digital coronagraphy underneath PRAIA, used in the reduction of stellar occultations, rotational light curves, mutual phenomena and natural satellite observations. We highlight novelties developed by us and never before reported in the literature, which significantly enhance the precision and automation of photometry and digital coronagraphy, such as: (a) PRAIA’s pixelized aperture photometry (PCAP), which avoids pixel sub-sampling or fractioning; (b) fully automatic object
detection and aperture determination (BOIA), which abolishes the use of arbitrary sky background sigma factors, and finds better apertures than by using subjective FWHM factors; (c) better astrometry improving the aperture and coronagraphy centres, including the new Photogravity Center Method besides circular and elliptical Gaussian and Lorentzian generalized profiles; (d) coronagraphy of faint objects close to bright ones and vice-versa; e) use of elliptical rings for the coronagraphy of elongated profiles; (f) refined quartile ring statistics; (g) multiprocessing image capabilities for faster computation speed. We give examples showing the photometry performance, discuss the advantages of PRAIA over other popular packages for Solar System differential photometric observations, point out the uniqueness of its digital coronagraphy in comparison with other coronagraphy tools and methods, and comment about future planed implementations. Besides Solar System works, PRAIA can also be used in the differential photometry of variable and cataclysmic stars and transient phenomena like exoplanet transits and microlensing, and in the digital coronagraphy of astrophysical observations. PRAIA codes and input files are publicly available for the first time at:
https://ov.ufrj.br/en/PRAIA/.
Context. Every population of small bodies in the Solar System contains a sizable fraction of multiple systems. Of these, the Jupiter Trojans have the lowest number of known binary systems and they are the least well characterized.
Aims. We aim to characterize the reported binary system (17365) Thymbraeus, one of only seven multiple systems of Jupiter Trojans known.
Methods. We conducted light curve observing campaigns in 2013, 2015, and 2021 with ground-based telescopes. We modeled these light curves using dumbbell figures of equilibrium.
Results. We show that Thymbraeus is unlikely a binary system. Its light curves are fully consistent with a bilobated shape: a dumbbell equilibrium figure. We determine a low density of 830 ± 50 kg m ⁻³ , consistent with the reported density of other Jupiter-Trojan asteroids and small Kuiper belt objects. The angular velocity of Thymbraeus is close to fission. If separated, its components would become a similarly sized double asteroid, like the Jupiter-Trojan (617) Patroclus.
Over the last couple decades, numerous papers based on lightcurve observations of asteroids have derived shapes that were claimed to represent “contact binary” or fluid equilibrium figures. From these shapes, the authors then presumed to derive densities, or density limits, on such bodies. In this paper we remind that it is well established, theoretically as well as observationally, that lightcurve analysis alone, under practical limitations of phase angle and aspect range, in most cases cannot establish concavities of a figure, i.e., the resultant shape inversion is a convex hull, not an actual shape. Therefore, it is generally not possible to infer “bilobed” or “contact binary” shapes from lightcurve analysis alone, let alone infer densities from such analysis. We also show that even “rubble pile” strength overrides fluid equilibrium for all but the very largest asteroids or TNOs. As a result, supposing Jacobi ellipsoidal or Roche near-contact figures and inferring densities therefrom is not justified.
In this paper, we present masses of 103 asteroids deduced from their perturbations on the orbits of the inner planets, in particular Mars and the Earth. These determinations and the INPOP19a planetary ephemerides are improved by the recent Mars orbiter navigation data and the updated orbit of Jupiter based on the Juno mission data. More realistic mass estimates are computed by a new method based on random Monte Carlo sampling that uses up-to-date knowledge of asteroid bulk densities. We provide masses with uncertainties better than 33${{\ \rm per\ cent}}$ for 103 asteroids. Deduced bulk densities are consistent with those observed within the main spectroscopic complexes.
Disk-integrated photometric data of asteroids do not contain accurate information on shape details or size scale. Additional data such as disk-resolved images or stellar occultation measurements further constrain asteroid shapes and allow size estimates. We aim to use all available disk-resolved images of about forty asteroids obtained by the Near-InfraRed Camera (Nirc2) mounted on the W.M. Keck II telescope together with the disk-integrated photometry and stellar occultation measurements to determine their volumes. We can then use the volume, in combination with the known mass, to derive the bulk density. We download and process all asteroid disk-resolved images obtained by the Nirc2 that are available in the Keck Observatory Archive (KOA). We combine optical disk-integrated data and stellar occultation profiles with the disk-resolved images and use the All-Data Asteroid Modeling (ADAM) algorithm for the shape and size modeling. Our approach provides constraints on the expected uncertainty in the volume and size as well. We present shape models and volume for 41 asteroids. For 35 asteroids, the knowledge of their mass estimates from the literature allowed us to derive their bulk densities. We clearly see a trend of lower bulk densities for primitive objects (C-complex) than for S-complex asteroids. The range of densities in the X-complex is large, suggesting various compositions. Moreover, we identified a few objects with rather peculiar bulk densities, which is likely a hint of their poor mass estimates. Asteroid masses determined from the Gaia astrometric observations should further refine most of the density estimates.
In the previous chapter, we investigated the equilibrium of rubble-pile satellites. This extended Darwin’s first problem, viz., the equilibrium shapes of fluid satellites of massive aspherical primaries to granular aggregates. We now proceed to generalize Darwin’s second problem by investigating the ellipsoidal equilibrium shapes of rubble binaries. We will apply the results to several known binary near-Earth asteroids.
We present an overview of the scientific potential of MATISSE, the Multi Aperture mid-Infrared SpectroScopic Experiment for the Very Large Telescope Interferometer. For this purpose we outline selected case studies from various areas, such as star and planet formation, active galactic nuclei, evolved stars, extrasolar planets, and solar system minor bodies and discuss strategies for the planning and analysis of future MATISSE observations. Moreover, the importance of MATISSE observations in the context of complementary high-angular resolution observations at near-infrared and submillimeter/millimeter wavelengths is highlighted.
Spectroscopic investigations of primitive asteroid families constrain family evolution and composition and conditions in the solar nebula, and reveal information about past and present distributions of volatiles in the solar system. Visible and near-infrared studies of primitive asteroid families have shown spectral diversity between and within families. Here, we aim to better understand the composition and physical properties of two primitive families with vastly different ages: ancient Themis (~2.5 Gyr) and young Veritas (~8 Myr). We analyzed the 5 - 14 μm Spitzer Space Telescope spectra of 11 Themis-family asteroids, including eight previously studied by Licandro et al. (2012), and nine Veritas-family asteroids, for a total of 20 asteroids in our sample. We detect a broad 10-μm emission feature, attributed to fine-grained and/or porous silicate regolith, in all 11 Themis-family spectra and six of nine Veritas-family asteroids, with 10-μm spectral contrast ranging from 1% ± 0.1% to 8.5% ± 0.9%. We used thermal modeling to derive diameters, beaming parameters and albedos for our sample. Asteroids in both families have beaming parameters near unity and geometric albedos in the range 0.03 - 0.14. Spectral contrast of the 10-μm silicate emission feature is correlated with beaming parameter and rotation period in the Themis family, and may be related to near-infrared spectral slope for both families. We see no correlations of 10-μm emission with diameter or albedo for either family. Comparison with laboratory spectra of primitive meteorites suggests these asteroids are similar to meteorites with relatively low abundances of phyllosilicates. Overall, our results suggest the Themis and Veritas families are primitive asteroids with variation in composition and/or regolith properties within both families.
Many members of the Themis family show evidence of hydration in the form of oxidized iron in phyllosilicates (Florczak, M. et al. [1999]. Astron. Astrophys. Suppl. Ser. 134, 463–471), and OH-bearing minerals (Takir, D., Emery, J.P. [2012]. Icarus 219, 641–654). The largest member, (24) Themis, has H2O ice covering its surface (Campins, H. et al. [2010]. Nature 464, 1320–1321; Rivkin, A.S., Emery, J.P. [2010]. Nature 464, 1322–1323). We have investigated the second largest Themis-family asteroid, (90) Antiope, which Castillo-Rogez and Schmidt (Castillo-Rogez, J.C., Schmidt, B.E. [2010]. Geophys. Res. Lett. 37, L10202) predict to have a composition that includes water ice and organics. We obtained 2–4-μm spectroscopy of (90) Antiope in 2006 and 2008, and we find an absorption in the 3-μm region clearly present in our 2008 spectrum and likely in our 2006 spectrum. Both spectra have rounded, bowl-shaped absorptions consistent with those ascribed to water ice as in the spectrum of Asteroid (24) Themis. We also present and compare Spitzer 8–12-μm mid-infrared spectra of (24) Themis and (90) Antiope. We find that (90) Antiope is lacking a “fairy castle” dusty surface, which is in contrast to (24) Themis, other Themis family members (Licandro, J. et al. [2012]. Astron. Astrophys. 537, A73), and Jupiter Trojans (e.g. Emery, J.P., Cruikshank, D.P., Van Cleve, J. [2006]. Icarus 182, 496–512). We conclude that the surface structure of (90) Antiope is most similar to Cybele Asteroid (121) Hermione (Hargrove, K.D. et al. [2012]. Icarus 221, 453–455).
This paper investigates the periodic motion of a particle in the doubly synchronous binary asteroid systems. Two typical doubly synchronous systems, 809 Lundia and 3169 Ostro, are discussed in detail. Under the Roche figure assumption, the two bodies of doubly synchronous system can be modeled as two triaxial ellipsoids. The Ivory’s theorem is used to derive the gravitational potential of the system. Then, a global numerical method, which combines grid searching and differential correction, is developed for systematically searching periodic orbits in the doubly synchronous systems. A total of 30 and 28 families of periodic orbits around Lundia and Ostro are found, respectively. Furthermore, on the basis of the analysis of morphology, stabilities and invariant manifolds, the potential applications of these periodic orbit families are studied. Several quasi-circular orbit families with low instability index are found to be suitable for the observation of the two typical binary systems. The invariant manifolds of some periodic orbits near the equilibrium points can provide the fuel-free trajectories to achieve the ballistic landing to the surface of the asteroids and transfer between the binary asteroids.
In this work, we investigate the equilibrium figures of a dumb-bell-shaped sequence with which we are still not well acquainted. Studies have shown that these elongated and nonconvex figures may realistically replace the classic “Roche binary approximation” for modeling putative peanut-shaped or contact binary asteroids. The best-fit dumb-bell shapes, combined with the known rotational period of the objects, provide estimates of the bulk density of these objects. This new class of mathematical figures has been successfully tested on the observed light curves of three noteworthy small bodies: main-belt Asteroid 216 Kleopatra, Trojan Asteroid 624 Hektor and Edgeworth–Kuiper-belt object 2001 QG298. Using the direct observations of Kleopatra and Hektor obtained with high spatial resolution techniques and fitting the size of the dumb-bell-shaped solutions, we derived new physical characteristics in terms of equivalent radius, 62.5 ± 5 km and 92 ± 5 km, respectively, and bulk density, 4.4 ± 0.4 g cm−3 and 2.43 ± 0.35 g cm−3, respectively. In particular, the growing inadequacy of the radar shape model for interpreting any type of observations of Kleopatra (light curves, AO images, stellar occultations) in a satisfactory manner suggests that Kleopatra is more likely to be a dumb-bell-shaped object than a “dog-bone.”
We present a new non-convex model of the 90 Antiope binary asteroid, derived with a modified version of the Shaping Asteroids
with Genetic Evolution (SAGE) method using disc-integrated photometry only. A new variant of the SAGE algorithm capable of
deriving models of binary systems is described. The model of 90 Antiope confirms the system's pole solution (λ = 199°, β = 38°,
σ = ±5°) and the orbital period (16.505 046 ± 0.000 005 h). A comparison between the stellar occultation chords obtained during
the 2011 occultation and the projected shape solution has been used to scale the model. The resulting scaled model allowed
us to obtain the equivalent radii (R1 = 40.4 ± 0.9 km and R2 = 40.2 ± 0.9 km) and the distance between the two system components (176 ± 4 km), leading to a total system mass of (9.14 ±
0.62) · 1017 kg. The non-convex shape description of the components permitted a refined calculation of the components’ volumes, leading
to a density estimation of 1.67 ± 0.23 g cm−3. The intermediate-scale features of the model may also offer new clues on the components’ origin and evolution.
Recently, the spinning tethered system is regarded as a typical and
fundamental space structure attracting great interest of the aerospace
engineers, and has been discussed primarily for specific space missions in past
decades, including on-orbit capture and propellantless orbit transfer etc. The
present work studies the dynamical behaviours of a fast spinning tethered
binary system under central gravitational field, and derives principles of the
basic laws of orbital maneuver. Considering the characteristics of coupled
librational and orbital motions, an averaging method is introduced to deal with
the slow-fast system equation, thus a definite equivalent model is derived. The
general orbit motion is completely determined analytically, including the orbit
geometry, periodicity, conversations and moving region etc. Since the
possibility of orbit control using tether reaction has been proved by previous
studies, special attention is paid to the transportation mode of angular
momentum and mechanical energy between the orbit and libration. The effect of
tether length change on the orbit shape is verified both in the averaged model
and original model. The results show the orbit angular momentum and mechanical
energy can be controlled independently, and the operating principles of tether
reactions are derived for special modification of orbit shape.
Telescopic observation of binary system of (809) Lundia in the in the 0.8–2.5 μm spectral range is presented in order to determine
its physical and mineralogical parameters. Observations covering several oppositions were performed using NASA telescope Infrared
Telescope Facility and SpeX spectrograph. One of these spectra was observed during a mutual event (an occultation between
components). A detailed analysis of spectra was performed using m4ast tools. (809) Lundia complex is a V-type object having similar mineralogy on both components of the system. By applying different
mineralogical models a composition similar to the one of howardite–diogenite meteorites was found. The comparison of composite
visible and near-infrared spectra with meteorites from Relab data base confirms this solution. From this comparison a surface
covered by fine dusty regolith with grain size less than 100 μm was found. Orthopyroxene is the most abundant pyroxene of
the regolith. Howarditic and diogenitic minerals seem to be the most abundant on the surface of (809) Lundia. The discrepancy
between howardite–eucrite–diogenite meteorite bulk density and the one computed for the binary system suggests a rubble pile
structure of both components.
PRAIA performs high precision differential photometry and astrometry on
digitized images (CCD frames, Schmidt plate surveys, etc). The package
main characteristics are automation, accuracy and processing speed.
Written in FORTRAN 77, it can run in scripts and interact with any
visualization and analysis software. PRAIA is in cope with the ever
growing amount of observational data available from private and public
sources, including data mining and next generation fast telescope all
sky surveys, like SDSS, Pan-STARRS and others. PRAIA was officially
assigned as the astrometric supporting tool for participants in the
GAIA-FUNSSO activities and will be freely available for the astronomical
community.
At the IAU XXVI General Assembly in 2006, the Division I decided to
create the Working Group on Astrometry by Small Ground-Based Telescopes
(WG-ASGBT). Its scientific goals are to foster the follow-up of small
bodies detected by the large surveys including the NEOs; to set-up a
dedicated observation network for the follow-up of objects which will be
detected by Gaia; to contribute to the observation campaigns of the
mutual events of natural satellites, stellar occultations, and binary
asteroids; and to encourage teaching astrometry for the next generation.
The present report gives the main activities carried out in these areas
with small telescopes (diameter less than 2m).
In this paper, we discuss dust motion and investigate possible mass transfer of charged particles in a binary asteroid system, in which the asteroids are electrically charged due to solar radiation. The surface potential of the asteroids is assumed to be a piecewise function, with positive potential on the sunlit half and negative potential on the shadow half. We derive the nonautonomous equations of motion for charged particles and an analytic representation for their lofting conditions. Particle trajectories and temporary relative equilibria are examined in relation to their moving forbidden regions, a concept we define and discuss. Finally, we use a Monte Carlo simulation for a case study on mass transfer and loss rates between the asteroids.
We describe a new approach to estimate asteroid masses from planetary range measurements. The approach significantly simplifies the process of parameter estimation and allows an effective control of systematic errors introduced by the omission of asteroids from the dynamical model. All asteroid masses are adjusted individually thus avoiding the usual distinction between masses considered individually and masses based on densities within the C, S and M taxonomic classes. Regularization is achieved by accounting, on each mass, for a prior uncertainty determined from available estimations of asteroid diameters and densities.The new approach is used to fit the asteroid model of the JPL planetary ephemeris to Mars range data. The adjusted planetary solutions exhibit similar extrapolation capacity as previous releases of the JPL ephemeris. Up to 27 asteroid masses are determined to better than 35%. The masses agree well with estimates obtained independently by other authors. The determined masses are also robust with respect to cross-validation on a dataset with a shorter time-span and with respect to a different selection of asteroids in the model.
This document is part of Subvolume B ‘Solar System’ of Volume 4 ‘Astronomy, Astrophysics, and Cosmology’ of Landolt-Börnstein - Group VI ‘Astronomy and Astrophysics’. It contains: 4.3.1.1 Asteroid discoveries 4.3.1.2 Dynamical groupings 4.3.1.3 Asteroid taxonomy 4.3.1.4 Near-Earth asteroids and potentially hazardous asteroids 4.3.1.5 Asteroid families 4.3.1.6 Asteroids with satellites and asteroid densities 4.3.1.7 Asteroids with comet-like characteristics 4.3.1.8 Dwarf planets 4.3.1.9 Rendezvous and fly-by missions to asteroids 4.3.1.10 Asteroid naming conventions/numbering
We model the geophysical evolution of the Themis family parent body. This study is motivated by the recent detection of water ice at the surface of 24 Themis, the first detection of free water on the surface of an asteroid. The Themis family members display a variety of spectral properties and densities, a possible indication that their parent was differentiated at the time of break-up. Differentiation of the parent body is better explained if it accreted as a mixture of ice within a few My after the production of CAIs. From these models we highlight a number of issues that provide a strong rationale for further ground-based and future space exploration of that family.
Non-destructive, non-contaminating, and relatively simple procedures can be used to measure the bulk density, grain density, and porosity of meteorites. Most stony meteorites show a relatively narrow range of densities, but differences within this range can be useful indicators of the abundance and oxidation state of iron and the presence or absence of volatiles. Typically, ordinary chondrites have a porosity of just under 10%, while most carbonaceous chondrites (with notable exceptions) are more than 20% porous. Such measurements provide important clues to the nature of the physical processes that formed and evolved both the meteorites themselves and their parent bodies. When compared with the densities of small solar system bodies, one can deduce the nature of asteroid and comet interiors, which in turn reflect the accretional and collisional environment of the early solar system.
Many small ground-based telescopes (with diameter less than 2m) allow us to perform programs of observations well adapted to astrometric measurements. The improvement of limiting magnitudes thanks to the use of CCD detector and their availability make them very useful for follow-up programs or observations on alert. This communication gives several examples of research carried out by members of the IAU working group “Astrometry by small ground-based telescopes”. We also propose setting up of a network of observers for the Gaia follow-up observations.
As an application of our recent observational error model, we present the astrometric masses of 26 main-belt asteroids. We also present an integrated ephemeris of 300 large asteroids, which was used in the mass determination algorithm to model significant perturbations from the rest of the main belt. After combining our mass estimates with those of other authors, we study the bulk porosities of over 50 main-belt asteroids and observe that asteroids as large as 300 km in diameter may be loose aggregates. This finding may place specific constraints on models of main-belt collisional evolution. Additionally, we observe that C-group asteroids tend to have significantly higher macroporosity than S-group asteroids.
We show that candidate contact binary asteroids can be efficiently identified from sparsely sampled photometry taken at phase angles α > 60°. At high phase angle, close/contact binary systems produce distinctive light curves that spend most of the time at maximum or minimum (typically >1 mag apart) brightness with relatively fast transitions between the two. This means that a few (approximately five) sparse observations will suffice to measure the large range of variation and to identify candidate contact binary systems. This finding can be used in the context of all-sky surveys to constrain the fraction of contact binary near-Earth objects. High phase angle light-curve data can also reveal the absolute sense of the spin.
The techniques described in an earlier paper were used to determine masses of 104 asteroids by the method of asteroid-asteroid gravitational interaction. For each of the 104 perturbers, 4 large sets of test particles selected by different criteria were used to calculate 4 mass values from a weighted mean of individual results within each set. The sheer number of test particles and observations ameliorates the effects of random observational errors and the type of systematic errors known to have affected specific observatories at specific times. It also reduces the effect of mismodeled attractions by perturbers other than the one being estimated, because the various test particles are affected to different degrees and in different directions. For most of the perturbers that have been analyzed by others, the results of this study agree reasonably well with values published in the past decade, giving credence to the approach. Thirty-eight of the results appear to be the first published masses for the respective asteroids, and 12 are the first determinations based on asteroid-asteroid interactions. Unrealistic and/or negative masses were obtained for some perturbers. Causes for this phenomenon are discussed and various means to obtain reasonable numbers are evaluated.
Many binary minor planets (BMPs; both binary asteroids and binary trans-Neptunian objects) are known to exist in the solar system. The currently observed orbital and physical properties of BMPs hold essential information and clues about their origin, their evolution, and the conditions under which they evolved. Here, we study the orbital properties of BMPs with currently known mutual orbits. We find that BMPs are typically highly inclined relative to their orbit around the Sun, with a distribution consistent with an isotropic distribution. BMPs not affected by tidal forces are found to have high eccentricities with non-thermal eccentricity distribution peaking at intermediate eccentricities (typically 0.4-0.6). The high inclinations and eccentricities of the BMPs suggest that BMPs evolved in a dense collisional environment, in which gravitational encounters in addition to tidal and secular Kozai effects played an important role in their orbital evolution.
In order to gain further insight into their surface compositions and relationships with meteorites, we have obtained spectra for 17 C and X complex asteroids using NASA's Infrared Telescope Facility and SpeX infrared spectrometer. We augment these spectra with data in the visible region taken from the on-line databases. Only one of the 17 asteroids showed the three features usually associated with water, the UV slope, a 0.7 mu m feature and a 3 mu m feature, while five show no evidence for water and 11 had one or two of these features. According to DeMeo et al. (2009), whose asteroid classification scheme we use here, 88% of the variance in asteroid spectra is explained by continuum slope so that asteroids can also be characterized by the slopes of their continua. We thus plot the slope of the continuum between 1.8 and 2.5 mu m against slope between 1.0 and 1.75 mu m, the break at similar to 1.8 mu m chosen since phyllosilicates show numerous water-related features beyond this wavelength. On such plots, the C complex fields match those of phyllosilicates kaolinite and montmorillonite that have been heated to about 700 degrees C, while the X complex fields match the fields for phyllosilicates montmorillonite and serpentine that have been similarly heated. We thus suggest that the surface of the C complex asteroids consist of decomposition products of kaolinite or montmorillonite while for the X complex we suggest that surfaces consist of decomposition products of montmorillonite or serpentine. On the basis of overlapping in fields on the continuum plots we suggest that the CI chondrites are linked with the Cgh asteroids, individual CV and CR chondrites are linked with Xc asteroids, a CK chondrite is linked with the Ch or Cgh asteroids, a number of unusual CI/CM meteorites are linked with C asteroids, and the CM chondrites are linked with the Xk asteroids. The associations are in reasonable agreement with chondrite mineralogy and albedo data.
The results of photometric observations of (87) Sylvia, 2006 VV2, (90) Antiopa, and (39) Laetitia asteroids in 2006–2008 are
presented. The specific features of light curves are considered for each object. In particular, for asteroid (87) Sylvia,
possible mutual phenomena in this triple system are identified. Asteroid 2006 VV2 manifests a strong dependence of the light
curve on the filter color, which testifies to the presence of inhomogeneities on its surface. The previously unknown brightness
variation period with a duration of about three days was obtained for this asteroid. For binary asteroid (90) Antiopa, the
strong dependence of its brightness on the phase angle was noticed; this may testify to the very flattened shape of its components.
Considerable time variations of the shape of the light curve for asteroid (39) Laetitia may testify either to its complex
shape or to its binary character.
Radar is a uniquely powerful source of information about the physical properties and orbits of asteroids. Measurements of the distribution of echo power in time delay (range) and Doppler frequency (radial velocity) produce two-dimensional images that can provide spatial resolution as fine as a decameter if the echoes are strong enough. With adequate orientational coverage, such images can be used to construct detailed three-dimensional models, define the rotation state precisely, and constrain the object's internal density distribution. As of May 2002, radar signatures have been measured for 75 main-belt asteroids (MBAs) and 105 near-Earth asteroids (NEAs). We summarize specific results for radar-detected asteroids, which span 4 orders of magnitude in diameter and rotation period. Radar has revealed both stony and metallic objects, principal-axis and complex rotators, smooth and extremely rough surfaces, objects that must be monolithic and objects that probably are not, spheroids and highly elongated shapes, contact-binary shapes, and binary systems. Radar also has expanded accurate orbit-prediction intervals for NEAs by as much as several centuries.
The original idea of Farinella et al. [1] that rubble pile asteroids can have figures of equilibrium, is rehabilitated. Albeit asteroids generally have a broad distribution of shapes and do not follow sequences of (hydrostatic) equilibrium, we show that some asteroids are indeed Jacobi or Darwin ellipsoids. Such statement is obtained from an analysis of their ellipsoidal shape (a:b:c) together with recent measures of their mass and bulk density [2,3]. This means that both their shape and adimensional rotation frequency sbond Omega =Omega /(pi rho G) follow sequences of equilibrium [4,5]. Jacobi and Darwin figures are obtained for uniformly rotating mass of (inviscid as well as compressible) fluids and relatively large angular momentum. Interestingly these objects appear to preferably be binaries. We moreover show that the porosity of such objects is relatively large (approx. 40%) indicating that they are loose rubble piles, yet with dense packing. Last we show that, given the observed bulk-densities, these bodies must be homogeneous bodies of uniform density distribution. Thus, though solid-solid friction must occur in such aggregates, the surface of these bodies is a surface of level similar to that of inviscid fluids. Comparison to other asteroids of similar mass either possessing a moonlet or with no known satellites should shed light on their formation history and/or constrains on collisional evolution. Binaries with low eccentricities and inclination (hence prograde orbit) should preferably be the outcome of catastrophic disruption as is supposed for members of dynamical family [6,7]. Future work and analysis of the typical reaccumulation time scales, typical angular momentum, possible post-reaccumulation cosmic shaking, etc. shall help to know how the fate of collisions or catastrophic breakup of a parent body can differ yielding to binaries with equilibrium figures. In any case the existence of a figure of equilibrium appears to be highly correlated to the presence of a moonlet or companion. We give a list of possible additional candidates that will be analysed in future observations with the HST/FGS interferometer. References: [1] Farinella P. et al. (1981). Icarus 46, 114. [2] Marchis F. et al. (2005). ACM. O-11.1. [3] Merline W. (2002). In: Asteroids III. p. 289. [4] Chandrasekhar S. (1987). Ellipsoidal figures of equilibrium. Dover. [5] Lai D. et al. (1993). ApjS 88, 205. [6] Michel P. et al. (2001). Science 295, 1696. [7] Michel P. et al. (2003). Nature 421, 608.
Lightcurves of the binary asteroid 90 Antiope were obtained at two observatories (Borowiec and Pic du Midi) on 14 nights in September through November 2000. The synodical period was found to be 16.496 +/- 0.001 hours and the observed amplitude of brightness variation was 0.08 mag. This amplitude was due to the noncircular shapes of the components of the binary system rather than to mutual occultations. Some predictions of a possibility of observations of the eclipsing events during future oppositions have also been made.
Three hypotheses concerning the origin of asteroids were examined, viz. that the asteroids are collisional fragments deriving from a few primaeval planetoids; that they are the remnants of a planet which disrupted; and that they are in process of forming a single body by random aggregation.
Monte Carlo simulations and theoretical arguments were used to predict mass distributions and rotation periods. It was found that the accretion hypothesis was not in good agreement with observations; but that both the collisional fragmentation and exploded planet theories were consistent with the observed asteroidal rotations and mass distribution.
Physical arguments were used to show that accretion within the asteroid belt, through the intermediary of jet stream formation, is probably not taking place, and that the exploded planet hypothesis meets with severe difficulties.
It was concluded that, most probably, the asteroids are debris arising from the collisional shattering of a few primal bodies, some of which may still survive intact.
We present images of two asteroid companions from adaptive optics (AO)
observations. These detections bring to four the number of binary
systems ever imaged, the previous discoveries being 243 Ida/Dactyl by
Galileo in 1993 (Belton et al./ 1995, Nature 374, 785) and 45
Eugenia/Petit-Prince in 1998 (Merline et al./ 1999, Nature 401, 565). A
satellite of 762 Pulcova was discovered on 2000 Feb 22 UT at the
Canada-France-Hawaii Telescope (CFHT) and was later confirmed by
additional observations at CFHT and Keck II. The satellite is about 4
mag fainter than the primary and our fit to the orbit indicates that it
was inclined approximately 60 deg to the line-of-sight, with a
semi-major axis of 800 km (0.6\arcsec) and a period of 4.0 days. We
derive a density for this FC-type primary of 1.8 g cm-3,
higher than our nominal value of 1.2 g cm-3 for F-type
Eugenia. On 2000 Aug 10 UT, Keck AO observations revealed that the
C-type 90 Antiope is a double asteroid, with similar-sized components,
separated by only 170 km (0.12\arcsec), with a brightness difference of
less than 0.1 mag. The co-orbiting pair was observed on 6 consecutive
nights and was found to have an orbital period of about 16.5 hours,
consistent with the established photometric ``rotation" period. While we
cannot rule out a very thin bridge of material connecting the two, we
show that it is not similar to the dumbbell-shaped 216 Kleopatra
reported by Ostro et al. 2000 (Science 288, 836). The two components are
clearly separated in the raw images, with a contrast consistent with the
PSF. We acquired similar images of Kleopatra before, during, and after
the radar observations of Ostro et al. Our Kleopatra images show a
bridge connecting the two components, but such a bridge is absent in our
Antiope images. This program is funded by NSF and NASA and uses CFHT
(French time), Keck Observatory (NASA time), and Mt. Wilson Observatory.
AbstractA review of observations and theories regarding binary asteroids and binary trans-Neptunian objects [collectively, binary minor planets (BMPs)] is presented. To date, these objects have been discovered using a combination of direct imaging, lightcurve analysis, and radar. They are found throughout the Solar System, and present a challenge for theorists modeling their formation in the context of Solar System evolution. The most promising models invoke rotational disruption for the smallest, shortest-lived objects (the asteroids nearest to Earth), consistent with the observed fast rotation of these bodies; impacts for the larger, longer-lived asteroids in the main belt, consistent with the range of size ratios of their components and slower rotation rates; and mutual capture for the distant, icy, trans-Neptunian objects, consistent with their large component separations and near-equal sizes. Numerical simulations have successfully reproduced key features of the binaries in the first two categories; ...
An asteroid family is a group of asteroids with similar orbits and spectra that was produced by a collisional breakup of a large parent body. To identify asteroid families, researchers look for clusters of asteroid positions in the space of proper orbital elements. These elements, being more constant over time than osculating orbital elements, provide a dynamical criterion of whether a group of bodies has a common ancestor. More than fifty asteroid families have been identified to date. Their analysis produced several important insights into the physics of large scale collisions, dynamical processes affecting small bodies in the Solar System, and surface and interior properties of asteroids.
We present a new method to solve the problem of initial orbit determination of any binary system. This method is mainly based
on the material available for an observer, for example relative positions at a given time of the couple in the “plane of sky”,
namely the tangent plane to the celestial sphere at the position of the primary component. The problem of orbit determination
is solved by splitting in successive stages in order to decorrelate the parameters of each other as much as possible. On one
hand, the geometric problem is solved using the first Kepler’s law from a single observing run and, on the other hand, dynamical
parameters are then inferred from the fit of the Kepler’s equation. At last, the final stage consists in determining the main
physical parameters involved in the secular evolution of the system, that is the spin axis and the J2 parameter of the primary if we assume that it is a quasi-spherical body. As a matter of fact there is no need to make too
restrictive initial assumptions (such as circular orbit or zero eccentricity) and initial guesses of parameters required by
a non-linear least-squares Levenberg–Marquardt algorithm are finally obtained after each stage. Such a protocol is very useful
to study systems like binary asteroids for which all of the parameters should be considered a priori as unknowns. As an example of application, we used our method to estimate the set of the Pluto–Charon system parameters from
observations collected in the literature since 1980.
Photometric data on 17 binary near-Earth asteroids (15 of them are certain detections, two are probables) were analysed and characteristic properties of the near-Earth asteroid (NEA) binary population were inferred. We have found that binary systems with a secondary-to-primary mean diameter ratio Ds/Dp⩾0.18 concentrate among NEAs smaller than 2 km in diameter; the abundance of such binaries decreases significantly among larger NEAs. Secondaries show an upper size limit of Ds=0.5–1 km. Systems with Ds/Dp⩽0.5 are abundant but larger satellites are significantly less common. Primaries have spheroidal shapes and they rotate rapidly, with periods concentrating between 2.2 to 2.8 h and with a tail of the distribution up to ∼4 h. The fast rotators are close to the critical spin for rubble piles with bulk densities about 2 g/cm3. Orbital periods show an apparent cut-off at Porb∼11 h; closer systems with shorter orbital periods have not been discovered, which is consistent with the Roche limit for strengthless bodies. Secondaries are more elongated on average than primaries. Most, but not all, of their rotations appear to be synchronized with the orbital motion; nonsynchronous secondary rotations may occur especially among wider systems with Porb>20 h. The specific total angular momentum of most of the binary systems is similar to within ±20% and close to the angular momentum of a sphere with the same total mass and density, rotating at the disruption limit; this suggests that the binaries were created by mechanism(s) related to rotation near the critical limit and that they neither gained nor lost significant amounts of angular momentum during or since formation. A comparison with six small asynchronous binaries detected in the main belt of asteroids suggests that the population extends beyond the region of terrestrial planets, but with characteristics shifted to larger sizes and longer periods. The estimated mean proportion of binaries with Ds/Dp⩾0.18 among NEAs larger than 0.3 km is 15±4%. Among fastest rotating NEAs larger than 0.3 km with periods between 2.2 and 2.8 h, the mean proportion of such binaries is (66+10−12)%.
The study of the equilibrium and stability of spinning ellipsoidal fluid bodies with gravity began with Newton in 1687, and continues to the present day. However, no smaller bodies of the Solar System are fluid. Here I model those bodies as elastic–plastic solids using a cohesionless Mohr–Coulomb yield envelope characterized by an angle of friction. This study began in Holsapple 2001. Here new closed-form algebraic formulas for the spin limits of ellipsoidal shapes are derived using an energy method. The fluid results of Maclaurin and Jacobi are again recovered as special cases. I then consider the stability of those equilibrium states. For elastic–plastic solids the common methods cannot be used, because the constitutive equations lack sufficient smoothness at the limiting plastic states. Therefore, I propose and study a new measure of the stability of dynamic processes in general bodies. An energy-based approach is introduced which is shown to include stability approaches used in the statics of nonlinear elastic and elastic–plastic bodies, spectral definitions and the Liapunov methods used for finite-dimensional dynamical systems. The method is applied to spinning, solid, strained bodies. In contrast to the special fluid case, it is found that the strain energy term of solid materials generally induces stability of all equilibrium shapes, except for two possible cases. First, strain softening in the elastic–plastic law can result in instability at the plastic limit spin. Second, a loss of shear stiffness can give unstable states at specific spins less than the limit equilibrium spins. In the latter case, a solid spinning ellipsoidal body without elastic shear stiffness can spin no faster than with a period of about 3.7 hr, else it will fail by shearing deformations. That is distinctly slower than the oft-quoted limit of 2.1 hr at which material would be flung off the equator by tensile forces. However, the final conclusion is that neither cohesion nor tensile strength is required for the shapes and spins of almost all of the larger observed asteroids: we cannot rule out rubble-pile structures.
The bodies of the Solar System exist in a variety of irregular shapes. Studies of those shapes are conducted to infer information about the internal composition, structure, and history of those bodies. However, such inferences require knowing how the composition and structure or history relates to the shape and internal forces. That connection is known only for fluid bodies, where the permissible equilibrium states were discovered centuries ago by Newton, Maclaurin, Jacobi, Poincaré, and Roche. While others have given results for linear elastic solid bodies, the elastic problem is not uniquely posed, since elastic solutions depend on an implicit assumption about the existence and shape of an initial stress-free state. The present states of Solar System bodies are a culmination of complicated past histories, possibly involving collisions, disruption, melting, accumulation, and large-scale yielding and reshaping. Such processes create underlying residual stress fields that cannot be known.
CCD observations of the binary asteroid 90 Antiope were carried out at seven observatories (Borowiec, Kharkiv, Pic du Midi, Chateau Renard, Les Engarouines, Ottmarsheim, and Durtal) on 31 nights from December 2002 through April 2003. The results show two-component lightcurves with each showing the same period of $16.505 \pm 0.002$ h. The first component is associated with the rotation of the two non-spherical bodies of the system; the second one is due to eclipses/occultations in the binary system. The lightcurves suggest that Antiope is an 'almost synchronous system' with orbital period of $16.5051 \pm 0.0002$ h and a little shorter rotational one of $16.5047 \pm 0.0002$ h. The ecliptic coordinates of the pole of the orbit system are $\lambda_{n} = 17\degr \pm 5\degr$ and $\beta_{n} = 25\degr \pm 5\degr$. A possibility of the observation of the eclipsing events during two future oppositions (April 2004 and July 2005) has been predicted.
Context. Aims.We present evidence that four minor planets of the main belt are binary systems. Methods.These discoveries are based on CCD photometric measurements made by many observers coordinated in a network of observatories. Results.Orbital and physical properties are derived from a total of 134 partial light curves involving 26 stations. (854) Frostia, (1089) Tama, (1313) Berna, and (4492) Debussy show mutual eclipses features on their light curves. In all cases, rotation and revolution are synchronous. Synodic periods are 37.728, 16.444, 25.464 and 26.606 h respectively. From a simple model, we have derived their bulk densities as follows: 0.89 $\pm$ 0.14, 2.52 $\pm$ 0.30, 1.22 $\pm$ 0.15 and 0.91 $\pm$ 0.10 g cm$^{-3}$ respectively. Uncertainties in the bulk densities, arising from scattering and shadow effects are not taken into account. These could increase the density estimates by a factor up to 1.6. Our method of determining bulk density is completely independent of their mass and their diameter estimates. The low rotational periods and the low bulk densities clearly imply a collisional process to explain this kind of binary asteroid. Based on our database of a few thousand light curves of minor planets, the population of similar-sized objects in the main belt is estimated to $6\pm 3$ percent in the 10–50 km diameter class. Conclusions.
The recent discovery of a binary asteroid during a spacecraft fly-by generated keen interest, because the orbital parameters of binaries can provide measures of the masses, and mutual eclipses could allow us to determine individual sizes and bulk densities. Several binary near-Earth, main-belt and Trojan asteroids have subsequently been discovered. The Kuiper belt-the region of space extending from Neptune (at 30 astronomical units) to well over 100 AU and believed to be the source of new short-period comets-has become a fascinating new window onto the formation of our Solar System since the first member object, not counting Pluto, was discovered in 1992 (ref. 13). Here we report that the Kuiper-belt object 1998 WW31 is binary with a highly eccentric orbit (eccentricity e approximately 0.8) and a long period (about 570 days), very different from the Pluto/Charon system, which was hitherto the only previously known binary in the Kuiper belt. Assuming a density in the range of 1 to 2 g cm-3, the albedo of the binary components is between 0.05 and 0.08, close to the value of 0.04 generally assumed for Kuiper-belt objects.
After decades of speculation, the existence of binary asteroids has been observationally confirmed, with examples in all minor planet populations. However, no triple systems have hitherto been discovered. Here we report the unambiguous detection of a triple asteroidal system in the main belt, composed of a 280-km primary (87 Sylvia) and two small moonlets orbiting at 710 and 1,360 km. We estimate their orbital elements and use them to refine the shape of the primary body. Both orbits are equatorial, circular and prograde, suggesting a common origin. Using the orbital information to estimate its mass and density, 87 Sylvia appears to have a rubble-pile structure with a porosity of 25-60 per cent. The system was most probably formed through the disruptive collision of a parent asteroid, with the new primary resulting from accretion of fragments, while the moonlets are formed from the debris, as has been predicted previously.
The Trojan population consists of two swarms of asteroids following the same orbit as Jupiter and located at the L4 and L5 stable Lagrange points of the Jupiter-Sun system (leading and following Jupiter by 60 degrees ). The asteroid 617 Patroclus is the only known binary Trojan. The orbit of this double system was hitherto unknown. Here we report that the components, separated by 680 km, move around the system's centre of mass, describing a roughly circular orbit. Using this orbital information, combined with thermal measurements to estimate the size of the components, we derive a very low density of 0.8(- 0.1)+0.2 g cm(-3). The components of 617 Patroclus are therefore very porous or composed mostly of water ice, suggesting that they could have been formed in the outer part of the Solar System.
After years of speculation, satellites of asteroids have now been shown
definitively to exist. Asteroid satellites are important in at least two
ways: (1) They are a natural laboratory in which to study collisions, a
ubiquitous and critically important process in the formation and
evolution of the asteroids and in shaping much of the solar system, and
(2) their presence allows to us to determine the density of the primary
asteroid, something which otherwise (except for certain large asteroids
that may have measurable gravitational influence on, e.g., Mars) would
require a spacecraft flyby, orbital mission, or sample return. Binaries
have now been detected in a variety of dynamical populations, including
near-Earth, main-belt, outer main-belt, Trojan, and transneptunian
regions. Detection of these new systems has been the result of improved
observational techniques, including adaptive optics on large telescopes,
radar, direct imaging, advanced lightcurve analysis, and spacecraft
imaging. Systematics and differences among the observed systems give
clues to the formation mechanisms. We describe several processes that
may result in binary systems, all of which involve collisions of one
type or another, either physical or gravitational. Several mechanisms
will likely be required to explain the observations.
CCD observations of the binary asteroid 90 Antiope were carried out at four observatories (Borowiec, Pic du Midi, Kharkiv, and Chateau Renard) on 26 nights from October 2001 through February 2002. The results show a two-component lightcurve with each showing the same period of 16.505 +/- 0.002 hours. The first component (with the amplitude of 0.10 mag) is associated with the rotation of two non-spherical bodies of the system; the second one, showing two sharp minima (with the amplitude in the range 0.05-0.12 mag, depending linearly on the phase angle) is due to eclipses in the binary system. The lightcurve suggests a synchronous rotation. The orientation of the system's orbit has been determined from the analysis of both the amplitudes and the duration of the eclipses. Some predictions of the possibility of observations of the eclipsing events during future oppositions have also been made.
We present an analysis of the distribution of asteroid spin rates vs. size. The existence of significant populations of both slow and fast rotators among asteroids smaller than D=40 km, and especially below 10 km (where our sample is mostly near-Earth asteroids), is shown. We have found that the excess of slow rotators is present at spin rates below ≈0.8 rev/day, and the group of fast rotators occupies the range of spin rates >7 rev/day. The fast rotators show interesting characteristics: The lack of objects rotating faster than 2.2 h period among asteroids with absolute magnitude H
Among the most fundamental physical characteristics of any planetary body are its density and porosity. Our data base of meteorite and density measurements have some interesting implications for future meteorite and asteroid studies.
We report on a campaign of adaptive optics observations which focuses on
121 Hermione, 45 Eugenia, and 90 Antiope binary asteroids performed with
ESO-VLT and Keck II telescopes in 2003-2004. A precessing Keplerian
model was used to describe the motion of their companion. The orbital
elements are determined accurately using data spanning more than 2
years. The satellite of 121 Hermione revolves at a= 775+/-14 km from the
primary in P=2.5714+/-0.001 days with a low eccentricity
(e=0.008+/-0.004) and retrograde orbit w.r.t. to the primary's equator
(i=175+/-4 deg considering a pole solution (1.9,13.2) deg in ecliptic
EQJ2000). The sense of revolution was unambiguously estimated from
images separated by a few hours. Keck AO data taken in December 2003
revealed the bi-lobated shape of the primary. The nominal bulk density
as derived from observed size of the primary and its 209 km IRAS
diameter is 1.2+/-0.3 g/cm3 (Marchis et al., Icarus, 2004). Future
observations with better angular resolution will allow us to see if 121
Hermione is a triple system. The orbit of Petit-Prince, moonlet of 45
Eugenia, was constrained using Feb. and Mar. 2004 AO data recorded at
the VLT (a=1196+/-4 km, P= 4.7244+/-0.001 days, e=0, i=163+/-6 deg with
a pole solution (133+/-3,-40+/-3 deg) in ecliptic B1950), leading to a
bulk density of 1.17 g/cm3 considering its 215 km IRAS diameter. Both
models predict successfully the positions reported for the discovery of
Petit-Prince on Nov. 1998 and of S/2001 (121) 1 by Merline et al. (1999
and 2002). We will also present results on the same-size binary asteroid
90 Antiope, using the same analysis. Feb. and Mar. 2004 VLT-NACO data
confirmed that both components are similar (with a Dm 2.4 and a diameter
of 110+/-16 km). A preliminary analysis of Feb. and Mar. 2004 VLT data
confirms that both components, separated by 170+/-1 km, with a
revolution period P=16.5268 +- 0.0001h, are quasi-similar (with a Dm
˜ 2.4% and a diameter of 110+/-16 km) leading to a low bulk
density of 0.6+/-0.2 g/cm3. NIR colors, shape of the primary, and
motions of the apsidal lines of these binaries will be discussed. This
work supported by the National Science Foundation Science and Technology
Center for Adaptive Optics, is based on observations collected at the
European Southern Observatory, Chile and Keck telescope, Hawaii.
The discovery of a probable satellite of a minor planet during the
occultation of a star on 7 June 1978 and additional photoelectric events
during another such occultation on 11 December 1978 have led to the
realization that anomalous sightings during previous occultations of
stars by minor planets are possibly also due to satellites. Some
features of minor planet lightcurves may be modeled in terms of the
rotation of contact binary asteroids, or in terms of eclipsing and
shadowing events by orbiting satellites. Calculations show that
satellites are gravitationally bound out to distances of about 100 times
the diameter of the primary. Although the large satellites are probably
collisionally stable over the solar system's lifetime, the time scales
for tidal evolution are much smaller, typically 10,000 to 10,000,000 yr.
A dynamical model for a minor planet, and by extension one for comets
and fireballs, is presented.
Asteroid 90 Antiope is binary, with widely separated equal-mass
components. Its high angular momentum may be due to a low-velocity
impact among Themis family members, but the probability of such a
collision is low, suggesting it is unique.
There is a growing view among planetary scientists that many if not most
of the small bodies of the solar system (including asteroids and comets)
are ``rubble piles'' held together by self-gravity rather than material
strength. In several cases, though, the assumption that asteroid rubble
piles should conform to figures of hydrostatic equilibrium leads to
unrealistically high inferred densities for those objects. I suggest
here that rubble piles should instead be explicitly considered as
granular materials, which behave very differently from fluids even on
large scales (as anyone who has walked among sand dunes can testify). I
demonstrate that even completely cohesionless particulate assemblies can
maintain shapes that are significantly different from figures of
hydrostatic equilibrium, so long as: 1) the difference between the local
surface normal and the local acceleration vector does not exceed the
angle of repose; and 2) internal stresses do not crush individual
particles.
Laboratory experiments and computer modeling are used to predict the
development of regoliths on all asteroids more than a few tens of
kilometers in diameter, allowing for a wide range in the intrinsic
strength of asteroidal surface materials. The high frequency of
interasteroid collisions requires nearly all asteroids to be fragments
of precursors.
Models of binary asteroids based on spherical components are inadequate
to analyze lightcurve data, since if the shape is determined by
self-gravitation, significant tidal distortions are present. On the
other hand, equilibrium binary models proposed so far (e.g. for 624
Hektor and 216 Kleopatra) are based on the arbitrary assumption of
equal-sized components. The authors present sequences of equilibrium
Roche binaries for values of the mass ratio between 0.01 and 1, and
discuss the application of these models to real asteroids. Two items of
particular interest are: (1) for asteroids of known rotational
properties, the equilibrium models allow to constrain the admissible
values of the mass ratio and density; (2) the models allow to describe
qualitatively the expected light curve morphology.
The discovery that many trans-Neptunian objects exist in pairs, or binaries, is proving invaluable for shedding light on the formation, evolution and structure of the outer Solar system. Based on recent systematic searches it has been estimated that up to 10 per cent of Kuiper-belt objects might be binaries. However, all examples discovered to date are unusual, as compared with near-Earth and main-belt asteroid binaries, for their mass ratios of the order of unity and their large, eccentric orbits. In this article we propose a common dynamical origin for these compositional and orbital properties based on four-body simulations in the Hill approximation. Our calculations suggest that binaries are produced through the following chain of events. Initially, long-lived quasi-bound binaries form by two bodies getting entangled in thin layers of dynamical chaos produced by solar tides within the Hill sphere. Next, energy transfer through gravitational scattering with a low-mass intruder nudges the binary into a nearby non-chaotic, stable zone of phase space. Finally, the binary hardens (loses energy) through a series of relatively gentle gravitational scattering encounters with further intruders. This produces binary orbits that are well fitted by Kepler ellipses. Dynamically, the overall process is strongly favoured if the original quasi-bound binary contains comparable masses. We propose a simplified model of chaotic scattering to explain these results. Our findings suggest that the observed preference for roughly equal-mass ratio binaries is probably a real effect; that is, it is not primarily due to an observational bias for widely separated, comparably bright objects. Nevertheless, we predict that a sizeable population of very unequal-mass Kuiper-belt binaries is probably awaiting discovery.
The Yarkovsky–O'Keefe–Radzievskii–Paddack (YORP) effect may spin up or spin down 5-km-radius asteroids on a 108-year timescale. Smaller asteroids spin up or down even faster due to the radius-squared dependence of the YORP timescale. The mechanism is the absorption of sunlight and its re-emission as thermal radiation from an irregularly shaped asteroid. This effect may compete with impacts and tidal encounters as a way of changing rotation rates for small asteroids, especially in the near-Earth region. The YORP effect may explain the rapid rotation of 1566 Icarus and the slow tumbling of 4179 Toutatis. It may explain to some extent the slow rotation of 253 Mathilde. Meteoroids spin up or down on timescales fast compared to their cosmic ray exposure ages.
We present a physical model to explain the existence of a class of large-lightcurve-amplitude, rapidly rotating asteroids found most commonly among objects in the size range 100–300 km diameter. A significant correlation between rotation period and lightcurve amplitude exists for asteroids in this size range in the sense that those with larger amplitudes spin more rapidly and hence these objects have high rotational angular momenta. Since this is a property of Jacobi ellipsoids, we have investigated whether these asteriods might be examples of triaxial equilibrium ellipsoids. We find that objects rotating with periods of 6 hr must have densities between 1.1 and 1.4 g cm−3, while those rotating in 4 hr would have densities between 2.4 and 3.2 g cm−3. If this model is valid then at least some of these asteroids have rather low mean densities. The reality of this result and its interpretation in terms of collisional evolution of the asteroids is discussed.
We present numerical simulations of near-Earth asteroid (NEA) tidal disruption resulting in bound, mutually orbiting systems. Using a rubble pile model we have constrained the relative likelihoods for possible physical and dynamical properties of the binaries created. Overall 110,500 simulations were run, with each body consisting of ∼1000 particles. The encounter parameters of close approach distance and velocity were varied, as were the bodies' spin, elongation and spin axis direction. The binary production rate increases for closer encounters, at lower speeds, for more elongated bodies, and for bodies with greater spin. The semimajor axes for resultant binaries are peaked between 5 to 20 primary radii, and there is an overall trend for high eccentricity, with 97% of binaries having e > 0.1. The secondary-to-primary size ratios of the simulated binaries are peaked between 0.1 and 0.2, similar to trends among observed asteroid binaries. The spin rates of the primary bodies are narrowly distributed between 3.5- and 6-h periods, whereas the secondaries' periods are more evenly distributed and can exceed 15-h periods. The spin axes of the primary bodies are very closely aligned with the angular momenta of the binary orbits, whereas the secondary spin axes are nearly random. The shapes of the primaries show a large distribution of axis ratios, where those with low elongation (ratio of long and short axis) are both oblate and prolate, and nearly all with large elongation are prolate. This work presents results that suggest tidal disruption of gravitational aggregates can make binaries physically similar to those currently observed in the NEA population. As well, tidal disruption may create an equal number of binaries with qualities different from those observed, mostly binaries with large separation and with elongated primaries.
The rotation period, pole direction, and scattering parameters of an asteroid can be deduced from its lightcurves simultaneously with the shape. Simulations and real data indicate that the result obtained with convex inversion is unique and stable if several lightcurves obtained at various geometries are available. Since the parameters of scattering laws such as the Hapke or Lumme–Bowell models cannot be determined well using lightcurves only, we introduce a simple empirical scattering law. This law can be applied in the computation of reference lightcurves and phase curves for further analysis of the physical properties of the surface. We present shape, pole, and period solutions for asteroids that have also been observed by space probes or radar.
We carried out new observations of the binary asteroid 22 Kalliope (S2/2001) with the Shane 3-m telescope of the Lick observatory in October and November 2001. With a FWHM (full width at half maximum) of 0″.2, Kalliope (apparent size of about 0″.15) was not resolved but it was possible to separate the secondary from its primary whose apparent separation was of the order of 0″.7 with a magnitude difference of 3.22±0.20. As each set of observations spanned a few days of time, they are well distributed along the secondary's orbit, enabling us to accurately estimate its orbit.The satellite orbits 22 Kalliope in a prograde manner with respect to Kalliope's rotational spin (which is in a retrograde sense relative to its orbit around the Sun), on a highly inclined (i=19.8±2.0 with respect to the equator of 22 Kalliope) and moderately eccentric orbit (e=0.07±0.02) with an orbital period of 3.58±0.08 days. The semi-major axis is 1020±40 km. Using Kalliope's diameter as determined from IRAS data, the asteroid's bulk density is about 2.03±0.16 g cm−3, suggestive of a highly porous body with a porosity of 70% considering that the grain density of its meteoritic analog is of ∼7.4 g cm−3. This suggests a rubble pile, rather than solid, body. The measured nodal precession rate of the secondary's orbit seems to be much higher than expected from Kalliope's oblateness, assuming a homogeneous body (constant density). This suggests that Kalliope may be 60% more elongated or 35% larger than presently believed or/and that its internal structure is highly inhomogeneous with a denser outer shell.
We report on Adaptive Optics observations of the satellite of Asteroid 121 Hermione with the ESO-Paranal UT4 VLT and the Keck AO telescopes. The binary system, belonging to the Cybele family, was observed during two observing campaigns in January 2003 and January 2004 aiming to confirm its trajectory and accurately determine its orbital elements. A precessing Keplerian model was used to describe the motion of S/2002 (121) 1. We find that the satellite of Hermione revolves at from the primary in days with a roughly circular and prograde orbit ( , w.r.t. equator primary). These extensive astrometric measurements enable us to determine the mass of Hermione to be and its pole solution ( , in ecliptic J2000). Additional Keck AO observations taken close to the asteroid opposition in December 2003 give us direct insight into the structure of the primary which presents a bilobated shape. Since the angular resolution is limited to the theoretical angular resolution of the telescope (43 mas corresponding to a spatial resolution of 80 km), two shape models (called snowman and peanut) are proposed based on the images which were deconvolved with MISTRAL deconvolution process. Assuming a purely synchronous orbit and knowing the mass of the primary, the peanut shape composed of two separated components is quite unlikely. Additionally the calculated from the analysis of the secondary orbit is not in agreement with the peanut model, but close to the snowman shape. The bulk density of the primary as derived from the observed size of the snowman shape is estimated to implying a porosity ∼14% for this C-type asteroid, corresponding to a fractured asteroid. Considering the IRAS diameter, the density is lower ( ) leading to a high porosity ( ) with a nominal value of , which indicates a completely loose rubble-pile structure for the primary. Further work is necessary to better constrain the size, shape, and then internal structure of Hermione's primary.
We present results of 161 numerical simulations of impacts into 100-km diameter asteroids, examining debris trajectories to search for the formation of bound satellite systems. Our simulations utilize a 3-dimensional smooth-particle hydrodynamics (SPH) code to model the impact between the colliding asteroids. The outcomes of the SPH models are handed off as the initial conditions for N-body simulations, which follow the trajectories of the ejecta fragments to search for the formation of satellite systems. Our results show that catastrophic and large-scale cratering collisions create numerous fragments whose trajectories can be changed by particle–particle interactions and by the reaccretion of material onto the remaining target body. Some impact debris can enter into orbit around the remaining target body, which is a gravitationally reaccreted rubble pile, to form a SMAshed Target Satellite (SMATS). Numerous smaller fragments escaping the largest remnant may have similar trajectories such that many become bound to one another, forming Escaping Ejecta Binaries (EEBs). Our simulations so far seem to be able to produce satellite systems qualitatively similar to observed systems in the main asteroid belt. We find that impacts of 34-km diameter projectiles striking at 3 km s−1 at impact angles of ∼30° appear to be particularly efficient at producing relatively large satellites around the largest remnant as well as large numbers of modest-size binaries among their escaping ejecta.
In order to systematically analyze the influence on asteroidal photometric lightcurves of large-scale deviations from triaxial ellipsoidal shapes, a general model is needed for which the variation of a few parameters can describe a wide range of irregular but “realistic” shapes. We adopted a model formed by merging together eight octants of ellipsoids having different semiaxes, with the constraint that adjacent octants must have two equal semiaxes in common. The corresponding lightcurves can then be computed by approximating the surface with a polyhedron formed by a finite number of plane facets. In several cases very irregular lightcurves are obtained, showing intriguing analogies with some puzzling lightcurves of real asteroids. In particular, the variation of lightcurve morphology with aspect angle can lead to changes in the number of extrema and/or an inversion of them, possibly implying an incorrect estimate of the spin axis direction and of the rotation period.
A sample of over 12,487 asteroid proper element triplets, computed by A. Milani and Z. Knežević (1994, Icarus 107, 219-254), has been searched for statistically significant and robust families by both the hierarchical clustering (HCM) and the wavelet analysis (WAM) automated techniques. The current sample includes almost 8000 unnumbered objects with relatively well-determined orbits, which allow us to extend the previous family classifications to much smaller asteroid sizes. With both clustering methods about one-third of the whole asteroid population is found to belong to groupings of varying significance and robustness. Nearly all the families identified in previous searches by Ph. Bendjoya (1993, Astron. Astrophys. Suppl. Ser. 102, 25-55) and V. Zappalà et al. (1994, Astron. J. 107, 772-801) are confirmed. Many more groupings are now recognized having a small number of members and/or a large percentage of unnumbered ones, particularly when the WAM technique is applied to asteroids located in the middle region of the main belt, between the 3:1 and the 5:2 Kirkwood gaps. Most of these new small families appear to derive from the (possibly recent) break-up of small parent asteroids, <50 km across. Some are very compact, suggesting ejection speeds not much in excess of the parent's escape velocity. Some fairly populous families can be readily interpreted as the outcome of giant cratering events, including those associated with (4) Vesta and (10) Hygiea. Others (e.g., Meliboea in the outer belt) are so depleted in small members that probably an old age is implied. Several populous families, and in particular those named "clans" (e.g., Eunomia, Vesta, Nysa), show a complex and size-dependent internal structure, suggesting a complex collisional history (i.e., multiple successive disruptive events). A problem with family searches applied to very numerous asteroid samples, such as the current one, is that neighboring, physically distinct groupings often partially overlap each other, and thus merge according to the clustering techniques.
We have performed new simulations of the formation of asteroid satellites by collisions, using a combination of hydrodynamical and gravitational dynamical codes. This initial work shows that both small satellites and ejected, co-orbiting pairs are produced most favorably by moderate-energy collisions at more direct, rather than oblique, impact angles. Simulations so far seem to be able to produce systems qualitatively similar to known binaries. Asteroid satellites provide vital clues that can help us understand the physics of hypervelocity impacts, the dominant geologic process affecting large main belt asteroids. Moreover, models of satellite formation may provide constraints on the internal structures of asteroids beyond those possible from observations of satellite orbital properties alone. It is probable that most observed main-belt asteroid satellites are by-products of cratering and/or catastrophic disruption events. Several possible formation mechanisms related to collisions have been identified: (i) mutual capture following catastrophic disruption, (ii) rotational fission due to glancing impact and spin-up, and (iii) re-accretion in orbit of ejecta from large, non-catastrophic impacts. Here we present results from a systematic investigation directed toward mapping out the parameter space of the first and third of these three collisional mechanisms.
A substantial body of indirect evidence suggests that some asteroids have satellites, although none has been detected unambiguously. Collisions between asteroids provide physically plausible mechanisms for the production of binaries, but these operate with low probability; only a small minority of asteroids are likely to have satellites. The abundance of binary asteorids can constrain the collisional history of the entire belt population. The allowed angular momentum of binaries and their rate of tidal evolution limit separations to no more than a few tens of the primary's radii. Their expected properties are consistent with failure to detect them by current imaging techniques.
The collisional evolution of various initial populations of asteroids is simulated numerically and compared with the present asteroid size-frequency distribution to find those populations which collisionally relax to the present belt. Both orbital and size distributions are treated, as well as the simultaneous evolution of two collisionally interacting populations with different physical properties. If the initial belt distribution was a power law, the initial belt population at the time when the present high-collision speed was established was probably only modestly larger than the present population. However, other distributions allow a more massive early belt. The rotational evolution due to collisions of asteroids with power-law distributions is also examined and compared with observations, leading to conclusions generally in agreement with those of size evolution. The high-collision speed in the present belt is likely due to Jupiter. Gravitational stirring by massive Jupiter-scattered planetesimals or secular resonances sweeping through the belt are the most probable mechanisms.
Results are presented for a general laboratory study of the limb darkening at small phase angles of various materials of planetary interest, with particular attention given to the wavelength dependence of limb darkening. Only substances stable at room temperature were measured, including basalt, graphite, mixtures of MgO and charcoal powders, olivine, goethite, bronzite, CaCO3, MgSO4, BaSO4, limonite, and hematite. Previous studies aimed at determining the nature of limb darkening at opposition for different common materials are reviewed. It is found that the scattering properties of most particulate materials near phase zero can be described adequately by Minnaert's law, but that such a representation is totally inadequate for materials that tend to fracture into flakes with mirrorlike surfaces (e.g., bronzite and graphite). The results also indicate that materials such as olivine have scattering properties within deep absorption bands which exhibit definite departures from Minnaert's law at large angles of incidence or emission.
The discovery of binaries in each of the major populations of minor bodies in the solar system is propelling a rapid growth of heretofore unattainable physical information. The availability of mass and density constraints for minor bodies opens the door to studies of internal structure, comparisons with meteorite samples, and correlations between bulk- physical and surface-spectral properties. The number of known binaries is now more than 70 and is growing rapidly. The relative sizes and separations of binaries in the different minor body populations point to more than one mechanism for forming bound pairs. Collisions appear to play a major role in the Main Belt. Rotational and/or tidal fission may be important in the Near Earth population. For the Kuiper Belt, capture in multi-body interactions may be the preferred formation mechanism. High angular resolution observations from space and from the ground are critical for detection of the relatively distant binaries in the Main Belt and the Kuiper Belt. Radar has been the most productive method for detection of Near Earth binaries. Lightcurve analysis is an independent technique that is capable of exploring phase space inaccessible to direct observations. Finally, spacecraft flybys have played a crucial paradigm-changing role with discoveries that unlocked this now-burgeoning field. Comment: 17 pages, 1 figure, 6 tables; Asteroids, Comets, Meteors 2005, Proceedings IAU Symposium 229
Discovery of companions to Asteroids 762 Pul-cova and 90 Antiope by direct imaging. Bull. Am. Astron. Soc. 32, 1017 Asteroids do have satellites
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Merline, W.J., Close, L.M., Dumas, C., Shelton, J.C., Menard, F., Chapman, C.R., Slater, D.C., 2000. Discovery of companions to Asteroids 762 Pul-cova and 90 Antiope by direct imaging. Bull. Am. Astron. Soc. 32, 1017. Abstract 13.06. Merline, W.J., Weidenschilling, S.J., Durda, D., Margot, J.L., Pravec, P., Storrs, A.D., 2002. Asteroids do have satellites. In: Bottke Jr., W.F., Cellino, A., Paolocchi, P., Binzels, R.P. (Eds.), Asteroids III. Univ. of Arizona Press, Tucson, pp. 289–312.
Figure of equilibrium among binary asteroids Equilibrium configurations of solid ellipsoidal cohe-sionless bodies
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Hestroffer, D., Tanga, P., 2005. Figure of equilibrium among binary asteroids. Bull. Am. Astron. Soc. 37, 1562. Holsapple, K.A., 2001. Equilibrium configurations of solid ellipsoidal cohe-sionless bodies. Icarus 154, 236–249.