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Journal ArticleDOI

Near Earth Asteroids with measurable Yarkovsky effect

01 May 2013-Icarus (Academic Press)-Vol. 224, Iss: 1, pp 1-13

AbstractWe seek evidence of the Yarkovsky effect among Near Earth Asteroids (NEAs) by measuring the Yarkovsky-related orbital drift from the orbital fit. To prevent the occurrence of unreliable detections we employ a high precision dynamical model, including the Newtonian attraction of 16 massive asteroids and the planetary relativistic terms, and a suitable astrometric data treatment. We find 21 NEAs whose orbital fits show a measurable orbital drift with a signal to noise ratio (SNR) greater than 3. The best determination is for asteroid (101955) 1999 RQ36, with an SNR ∼ 200. In some cases it is possible to constrain physical quantities otherwise unknown. Furthermore, the distribution of the detected orbital drifts shows an excess of retrograde rotators that can be connected to the delivery mechanism from the most important NEA feeding resonances and allows us to infer the obliquity distribution of NEAs. We discuss the implications of the Yarkovsky effect for impact predictions. In particular, for asteroid (29075) 1950 DA our results favor a retrograde rotation, which may have implications for the 2880 impact threat.

Topics: Yarkovsky effect (70%), Near-Earth object (58%), Retrograde motion (53%), Asteroid (53%), Orbit determination (51%)

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Citations
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Journal ArticleDOI
01 Jun 2014-Icarus
Abstract: The target asteroid of the OSIRIS-REx asteroid sample return mission, (101955) Bennu (formerly 1999 RQ 36), is a half-kilometer near-Earth asteroid with an extraordinarily well constrained orbit. An extensive data set of optical astrometry from 1999 to 2013 and high-quality radar delay measurements to Bennu in 1999, 2005, and 2011 reveal the action of the Yarkovsky effect, with a mean semimajor axis drift rate da=dt ¼ð � 19:0 � 0:1 Þ� 10

211 citations


Cites background or methods from "Near Earth Asteroids with measurabl..."

  • ...Given an estimated value of AT and the assumed value of d, one can readily derive the time-averaged da/dt using Gauss’ planetary equations (Farnocchia et al. 2013b)....

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  • ...As the Yarkovsky induced orbital drift depends on the osculating orbital elements (Farnocchia et al. 2013b), there are also commensurable variations in the da/dt evolution (see Fig....

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  • ...More recently Nugent et al. (2012) and Farnocchia et al. (2013b) have estimated the Yarkovsky effect for a few tens of near-Earth asteroids by using a formulation that depends on a single parameter to be determined from the orbital fit....

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  • ...The orbital predictions and the impact hazard assessment are then performed by a Monte Carlo simulation that accounts for both the Yarkovsky effect distribution and the orbital uncertainty (Farnocchia et al. 2013a; Farnocchia and Chesley 2014)....

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  • ...Importantly, it requires no information about the physical characteristics or spin state of the asteroid, and so it can be implemented readily in cases where only astrometric information is available (e.g., Vokrouhlický et al. 2008; Chesley et al. 2008; Nugent et al. 2012; Farnocchia et al. 2013b)....

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Journal ArticleDOI
01 Sep 2014-Icarus
TL;DR: A new approach to the asteroid family classification by combining the Hierarchical Clustering Method (HCM) with a method to add new members to existing families, which allows to solve some difficult cases of families overlapping in the proper elements space but generated by different collisional events.
Abstract: The number of asteroids with accurately determined orbits increases fast, and this increase is also accelerating. The catalogs of asteroid physical observations have also increased, although the number of objects is still smaller than in the orbital catalogs. Thus it becomes more and more challenging to perform, maintain and update a classification of asteroids into families. To cope with these challenges we developed a new approach to the asteroid family classification by combining the Hierarchical Clustering Method (HCM) with a method to add new members to existing families. This procedure makes use of the much larger amount of information contained in the proper elements catalogs, with respect to classifications using also physical observations for a smaller number of asteroids. Our work is based on a large catalog of high accuracy synthetic proper elements (available from AstDyS), containing data for >330,000 numbered asteroids. By selecting from the catalog a much smaller number of large asteroids, we first identify a number of core families; to these we attribute the next layer of smaller objects. Then, we remove all the family members from the catalog, and reapply the HCM to the rest. This gives both satellite families which extend the core families and new independent families, consisting mainly of small asteroids. These two cases are discriminated by another step of attribution of new members and by merging intersecting families. This leads to a classification with 128 families and currently 87,095 members. The number of members can be increased automatically with each update of the proper elements catalog; changes in the list of families are not automated. By using information from absolute magnitudes, we take advantage of the larger size range in some families to analyze their shape in the proper semimajor axis vs. inverse diameter plane. This leads to a new method to estimate the family age, or ages in cases where we identify internal structures. The analysis of the plot above evidences some open problems but also the possibility of obtaining further information of the geometrical properties of the impact process. The results from the previous steps are then analyzed, using also auxiliary information on physical properties including WISE albedos and SDSS color indexes. This allows to solve some difficult cases of families overlapping in the proper elements space but generated by different collisional events. The families formed by one or more cratering events are found to be more numerous than previously believed because the fragments are smaller. We analyze some examples of cratering families (Massalia, Vesta, Eunomia) which show internal structures, interpreted as multiple collisions. We also discuss why Ceres has no family.

180 citations


Journal ArticleDOI
14 Aug 2014-Nature
TL;DR: It is reported that the kilometre-sized asteroid (29075) 1950 DA is a rubble pile that is rotating faster than is allowed by gravity and friction and that the strengths of the forces are comparable to, though somewhat less than, the forces found between the grains of lunar regolith.
Abstract: Modelling and observations of the kilometre-sized asteroid (29075) 1950 DA reveal it to be a ‘rubble pile’ that is rotating faster than is allowed by gravity and friction; cohesive forces such as those in lunar regolith are required to prevent it breaking up. Some asteroids are solid bodies but others, known as 'rubble-pile' asteroids, are loose aggregates of sand- to boulder-sized components. The conventional view, that rubble piles are held together by gravitational and frictional forces alone, has recently been questioned. It has been suggested that small van der Waals forces between constituent grains may be an important factor. Here, Ben Rozitis et al. report that the kilometre-sized rubble-pile asteroid (29075) 1950 DA is rotating faster than the breakup limit for its density calculated assuming the action of gravity and friction alone. They conclude that inter-particle cohesive forces must be holding the asteroid together and that the forces are comparable to, though somewhat less than, those found between the grains of lunar regolith. Space missions1 and ground-based observations2 have shown that some asteroids are loose collections of rubble rather than solid bodies. The physical behaviour of such ‘rubble-pile’ asteroids has been traditionally described using only gravitational and frictional forces within a granular material3. Cohesive forces in the form of small van der Waals forces between constituent grains have recently been predicted to be important for small rubble piles (ten kilometres across or less), and could potentially explain fast rotation rates in the small-asteroid population4,5,6. The strongest evidence so far has come from an analysis of the rotational breakup of the main-belt comet P/2013 R3 (ref. 7), although that was indirect and poorly constrained by observations. Here we report that the kilometre-sized asteroid (29075) 1950 DA (ref. 8) is a rubble pile that is rotating faster than is allowed by gravity and friction. We find that cohesive forces are required to prevent surface mass shedding and structural failure, and that the strengths of the forces are comparable to, though somewhat less than, the forces found between the grains of lunar regolith.

154 citations


Journal ArticleDOI
01 Feb 2015-Icarus
Abstract: Asteroid (101955) Bennu, the target of NASA’s OSIRIS-REx sample return mission, is a D ≈ 0.5 km diameter low albedo near-Earth object. It has a spectral signature consistent with primitive carbonaceous chondrites, and an orbit similar to that of the Earth. A plausible evolution scenario for Bennu is that it migrated inward across the inner main belt from a low albedo family by Yarkovsky thermal forces over many hundreds of Myr. Eventually, it entered a resonance that took it into the terrestrial planet region, where a combination of planetary encounters and resonances took it to its current orbit over a few Myr to tens of Myr. When it departed the main belt, Bennu probably had an eccentricity 0.1 e 0.2 and an inclination 1 ° i 6 ° . Several low albedo families have the appropriate dynamical, color, albedo, and broad spectral characteristics to produce Bennu: Clarissa, Erigone, Eulalia, New Polana, and Sulamitis. Here we used a suite of numerical simulations to determine the ages of the families above, how Bennu reached its current orbit, and the most probable source family for Bennu. Specifically, we tracked test Bennu-like asteroids evolving in semimajor axis by the coupled Yarkovsky/YORP effects, incorporating a new formalism for how YORP torques modify the spin vector evolution of small asteroids. Using results and insights provided by Statler (Statler, T.S. [2009]. Icarus 202, 502–513), we assumed that modest shape changes to asteroids, produced by a variety of processes (e.g., crater formation, changes to asteroid rotational angular momentum by YORP), caused the test asteroids’ spin rates, but not their obliquities, to undergo a random walk. This “stochastic YORP” mechanism slows down how often asteroids reach YORP endstates (i.e., spinning up so fast that the asteroid sheds mass, spinning down so much the asteroid enters into a tumbling rotation state). This new model allowed us to reproduce the semimajor axis distribution of observed family members from Clarissa, Erigone, Eulalia, New Polana, and Sulamitis. In the process, we derived model family formation ages of ∼60 Myr old, 130 ± 30 Myr old, 830 - 100 + 370 Myr old, 1400 ± 150 Myr old, and 200 ± 40 Myr, respectively. Next, using a Monte-Carlo code to track millions of test asteroids from each of the families above to main belt escape routes capable of producing Bennu-like orbits, we found the most likely parent families for Bennu are Eulalia and New Polana. On average, more than twice as many 0.5 km objects from the New Polana family reach Bennu’s orbit as those from the Eulalia family. This corresponds to the New Polana and Eulalia families having a 70 - 4 + 8 % and 30 - 8 + 4 % probability of producing Bennu, respectively. Comparable runs to deduce the source of the Hayabusa 2 target, the low albedo 0.87 km diameter near-Earth object (162173) 1999 JU3, produced similar probabilities for both families. The former Marco-Polo-R target, the 1.9 km asteroid (175706) 1996 FG3, however, has a 85 - 83 + 4 % probability of coming from the Eulalia family and a 15 - 4 + 83 % probability of coming from the New Polana family. The reason for this switch is that 1996 FG3 may have been part of Yarkovsky/YORP-produced wave of like-sized bodies that is only now reaching the terrestrial planet region. We suggest that the top-like shape of Bennu is a byproduct of mass wasting and/or mass shedding events produced by YORP spin up during its long journey across the inner main belt.

124 citations


Cites background from "Near Earth Asteroids with measurabl..."

  • ...This leaves us with few direct constraints on the Yarkovsky drift rates of typical Bennu-sized bodies (e.g., Nugent et al., 2012; Farnocchia et al., 2013) and even less information on how they evolve in reaction to YORP (e.g., Vokrouhlický and Bottke, 2012)....

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  • ...Interestingly, the majority of NEOs like Bennu have retrograde spins ( 70%; La Spina et al., 2004; see also Nugent et al., 2012 and Farnocchia et al., 2013)....

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  • ...This leaves us with few direct constraints on the Yarkovsky drift rates of typical Bennu-sized bodies (e.g., Nugent et al., 2012; Farnocchia et al., 2013) and even less information on how they evolve in reaction to YORP (e....

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Journal ArticleDOI
15 Sep 2018-Icarus
Abstract: The debiased absolute-magnitude and orbit distributions as well as source regions for near-Earth objects (NEOs) provide a fundamental frame of reference for studies of individual NEOs and more complex population-level questions. We present a new four-dimensional model of the NEO population that describes debiased steady-state distributions of semimajor axis, eccentricity, inclination, and absolute magnitude H in the range 17 962 − 56 + 52 ( 802 − 42 + 48 × 10 3 ) NEOs with H

112 citations


References
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Abstract: New technological advances have made it feasible to conduct measurements with precision levels which are suitable for experimental tests of the theory of general relativity. This book has been designed to fill a new need for a complete treatment of techniques for analyzing gravitation theory and experience. The Einstein equivalence principle and the foundations of gravitation theory are considered, taking into account the Dicke framework, basic criteria for the viability of a gravitation theory, experimental tests of the Einstein equivalence principle, Schiff's conjecture, and a model theory devised by Lightman and Lee (1973). Gravitation as a geometric phenomenon is considered along with the parametrized post-Newtonian formalism, the classical tests, tests of the strong equivalence principle, gravitational radiation as a tool for testing relativistic gravity, the binary pulsar, and cosmological tests.

1,692 citations


Journal ArticleDOI
01 Apr 2002-Icarus
Abstract: The orbital and absolute magnitude distribution of the near-Earth objects (NEOs) is difficult to compute, partly because only a modest fraction of the entire NEO population has been discovered so far, but also because the known NEOs are biased by complicated observational selection effects. To circumvent these problems, we created a model NEO population which was fit to known NEOs discovered or accidentally rediscovered by Spacewatch. Our method was to numerically integrate thousands of test particles from five source regions that we believe provide most NEOs to the inner Solar System. Four of these source regions are in or adjacent to the main asteroid belt, while the fifth one is associated with the transneptunian disk. The nearly isotropic comets, which include the Halley-type comets and the long-period comets, were not included in our model. Test bodies from our source regions that passed into the NEO region (perihelia q<1.3 AU and aphelia Q≥0.983 AU) were tracked until they were eliminated by striking the Sun or a planet or were ejected out of the inner Solar System. These integrations were used to create five residence time probability distributions in semimajor axis, eccentricity, and inclination space (one for each source). These distributions show where NEOs from a given source are statistically most likely to be located. Combining these five residence time probability distributions with an NEO absolute magnitude distribution computed from previous work and a probability function representing the observational biases associated with the Spacewatch NEO survey, we produced an NEO model population that could be fit to 138 NEOs discovered or accidentally rediscovered by Spacewatch. By testing a range of possible source combinations, a best-fit NEO model was computed which (i) provided the debiased orbital and absolute magnitude distributions for the NEO population and (ii) indicated the relative importance of each NEO source region. Our best-fit model is consistent with 960±120 NEOs having H 2.8 AU), and ∼6% comes from the Jupiter-family comet region (2

687 citations


"Near Earth Asteroids with measurabl..." refers background or methods in this paper

  • ...This excess of retrograde rotators can be explained by the nature of resonance feeding into the inner Solar System (Bottke et al., 2002). Most of the primary NEA source regions (e.g., the 3:1 resonance, JFCs, Outer Belt, etc.) allow main belt asteroids to enter by drifting either inwards or outwards, but the m6 resonance is at the inner edge of the main belt and so asteroids can generally enter only by inwards drift, i.e., with retrograde rotation. Bottke et al. (2002) report that 37% of NEAs with absolute magnitude H < 22 arrive via m6 resonance. La Spina et al. (2004) point out that this implies 37% of NEAs have retrograde spin (via m6), plus half of the complement (via other pathways). Thus, the retrograde fraction should be 0.37 + 0.5 0.63 = 0.69, while La Spina et al. (2004) report 67% retrograde for their sample, which is dominated by large NEAs. Table 2 contains 81% retrograde rotators, which is larger than 69% and thus, at face value, appears to be inconsistent with the theory. The sample of asteroids shown in Table 2, however, is based on measured Yarkovsky mobility and is not a representative sample of the debiased NEA population as described by Bottke et al. (2002). For example, the sample is dominated by small PHAs (MOID < 0.05 AU) on fairly deep Earth-crossing orbits. We find that 9 of the 21 objects are Aten asteroids (43%), compared to the 6% fraction predicted for the debiased NEA population. Bottke et al. (2002) suggest that the majority of Atens ( 79%) should come from the innermost region of the main belt where the m6 resonance is located....

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  • ...This excess of retrograde rotators can be explained by the nature of resonance feeding into the inner Solar System (Bottke et al., 2002)....

    [...]

  • ...This excess of retrograde rotators can be explained by the nature of resonance feeding into the inner Solar System (Bottke et al., 2002). Most of the primary NEA source regions (e.g., the 3:1 resonance, JFCs, Outer Belt, etc.) allow main belt asteroids to enter by drifting either inwards or outwards, but the m6 resonance is at the inner edge of the main belt and so asteroids can generally enter only by inwards drift, i.e., with retrograde rotation. Bottke et al. (2002) report that 37% of NEAs with absolute magnitude H < 22 arrive via m6 resonance....

    [...]

  • ...This excess of retrograde rotators can be explained by the nature of resonance feeding into the inner Solar System (Bottke et al., 2002). Most of the primary NEA source regions (e.g., the 3:1 resonance, JFCs, Outer Belt, etc.) allow main belt asteroids to enter by drifting either inwards or outwards, but the m6 resonance is at the inner edge of the main belt and so asteroids can generally enter only by inwards drift, i.e., with retrograde rotation. Bottke et al. (2002) report that 37% of NEAs with absolute magnitude H < 22 arrive via m6 resonance. La Spina et al. (2004) point out that this implies 37% of NEAs have retrograde spin (via m6), plus half of the complement (via other pathways). Thus, the retrograde fraction should be 0.37 + 0.5 0.63 = 0.69, while La Spina et al. (2004) report 67% retrograde for their sample, which is dominated by large NEAs. Table 2 contains 81% retrograde rotators, which is larger than 69% and thus, at face value, appears to be inconsistent with the theory. The sample of asteroids shown in Table 2, however, is based on measured Yarkovsky mobility and is not a representative sample of the debiased NEA population as described by Bottke et al. (2002). For example, the sample is dominated by small PHAs (MOID < 0....

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  • ...Bottke et al. (2002) report that 37% of NEAs arrive via ν6 resonance....

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Journal ArticleDOI
Abstract: The Yarkovsky and YORP (Yarkovsky-O’Keefe-Radzievskii-Paddack) effects are thermal radiation forces and torques that cause small objects to undergo semimajor axis drift and spin vector modifications, respectively, as a function of their spin, orbit, and material properties. These mechanisms help to (a) deliver asteroids (and meteoroids) with diameter D < 40 km from their source locations in the main belt to chaotic resonance zones capable of transporting this material to Earth-crossing orbits; (b) disperse asteroid families, with drifting bodies jumping or becoming trapped in mean-motion and secular resonances within the main belt; (c) modify the rotation rates and obliquities of D < 40 km asteroids; and (d ) allow asteroids to enter into spin-orbit resonances, which affect the evolution of their spin vectors and feedback into the Yarkovsky-driven semimajor axis evolution. Accordingly, we suggest that nongravitational forces should now be considered as important as collisions and gravitational perturbations to our overall understanding of asteroid evolution.

587 citations


"Near Earth Asteroids with measurabl..." refers background in this paper

  • ...It is well known that nongravitational forces should be considered as important as collisions and gravitational perturbations for the overall understanding of asteroid evolution (Bottke et al., 2006)....

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01 Jan 1989
Abstract: The way an asteroid or other atmosphereless solar system body varies in brightness in response to changing illumination and viewing geometry depends in a very complicated way on the physical and optical properties of its surface and on its overall shape. This paper summarizes the formulation and application of recent photometric models by Hapke (1981, 1984, 1986) and by Lumme and Bowell (1981). In both models, the brightness of a rough and porous surface is parameterized in terms of the optical properties of individual particles, by shadowing between particles, and by the way in which light is scattered among collections of particles. Both models succeed in their goal of fitting the observed photometric behavior of a wide variety of bodies, but neither has led to a very complete understanding of the properties of asteroid regoliths, primarily because, in most cases, the parameters in the present models cannot be adequately constrained by observations of integral brightness alone over a restricted range of phase angles.

466 citations


Book
31 Jan 2003
Abstract: Foreword. Preface. Acknowledgments. Introduction. Time Scales and Time Differences. Planetary Ephemeris, Small-Body Ephemeris, and Satellite Ephemerides. Spacecraft Ephemeris and Partials File. Geocentric Space-Fixed Position, Velocity, and Acceleration Vectors of Tracking Station. Space-Fixed Position, Velocity, and Acceleration Vectors of a Landed Spacecraft Relative to Center of Mass of Planet, Planetary System, or the Moon. Algorithms for Computing ET-TAI. Light-Time Solution. Angles. Media and Antenna Corrections. Calculation of Precision Light Times and Quasar Delays. Partial Derivatives of Precision Light Times and Quasar Delays. Observables. References. Acronyms. Index.

364 citations