Near Earth Asteroids with measurable Yarkovsky effect
TL;DR: In this article, the Yarkovsky effect among near Earth asteroids (NEAs) was investigated by measuring the YARKovsky-related orbital drift from the orbital fit using a high precision dynamical model, including the Newtonian attraction of 16 massive asteroids and the planetary relativistic terms.
About: This article is published in Icarus.The article was published on 2013-05-01 and is currently open access. It has received 140 citations till now. The article focuses on the topics: Yarkovsky effect & Near-Earth object.
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TL;DR: In this paper, the authors describe the processing of the Gaia DR2 data, and describe the criteria used to select the sample published in Gaia DR 2, and explore the data set to assess its quality.
Abstract: Context. The Gaia spacecraft of the European Space Agency (ESA) has been securing observations of solar system objects (SSOs) since the beginning of its operations. Data Release 2 (DR2) contains the observations of a selected sample of 14,099 SSOs. These asteroids have been already identified and have been numbered by the Minor Planet Center repository. Positions are provided for each Gaia observation at CCD level. As additional information, complementary to astrometry, the apparent brightness of SSOs in the unfiltered G band is also provided for selected observations.Aims. We explain the processing of SSO data, and describe the criteria we used to select the sample published in Gaia DR2. We then explore the data set to assess its quality.Methods. To exploit the main data product for the solar system in Gaia DR2, which is the epoch astrometry of asteroids, it is necessary to take into account the unusual properties of the uncertainty, as the position information is nearly one-dimensional. When this aspect is handled appropriately, an orbit fit can be obtained with post-fit residuals that are overall consistent with the a-priori error model that was used to define individual values of the astrometric uncertainty. The role of both random and systematic errors is described. The distribution of residuals allowed us to identify possible contaminants in the data set (such as stars). Photometry in the G band was compared to computed values from reference asteroid shapes and to the flux registered at the corresponding epochs by the red and blue photometers (RP and BP).Results. The overall astrometric performance is close to the expectations, with an optimal range of brightness G ~ 12 − 17. In this range, the typical transit-level accuracy is well below 1 mas. For fainter asteroids, the growing photon noise deteriorates the performance. Asteroids brighter than G ~ 12 are affected by a lower performance of the processing of their signals. The dramatic improvement brought by Gaia DR2 astrometry of SSOs is demonstrated by comparisons to the archive data and by preliminary tests on the detection of subtle non-gravitational effects.
584 citations
TL;DR: The OSIRIS-REx asteroid sample return mission target, (101955) Bennu (formerly 1999 RQ 36), is a half-kilometer near-Earth asteroid with an extraordinarily well constrained orbit as mentioned in this paper.
238 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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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.
191 citations
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.
186 citations
TL;DR: In this article, the authors presented a new four-dimensional model of the near-Earth objects population that describes debiased steady-state distributions of semimajor axis, eccentricity, inclination, and absolute magnitude H in the range 17.962 − 56 + 52 + 52 ( 802 − 42 + 48 × 10 3 ) NEOs with H.
171 citations
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TL;DR: In this paper, a detailed thermophysical model (TPM) has been developed and extensively tested; this is the first detailed TPM shown to be applicable to NEA data, increasing the total number of NEAs with measured thermal inertia to 6.
Abstract: The subject of this work is the physical characterization of asteroids, focusing on the thermal inertia of near-Earth asteroids (NEAs). Thermal inertia governs the Yarkovsky effect, a non-gravitational force which significantly alters the orbits of asteroids up to \sim 20 km in diameter. Yet, very little has previously been known about the thermal inertia of small asteroids including NEAs. Observational and theoretical work is reported. The thermal emission of asteroids has been observed in the mid-infrared (5-35 {\mu}m) wavelength range using the Spitzer Space Telescope and the 3.0m IRTF. A detailed thermophysical model (TPM) has been developed and extensively tested; this is the first detailed TPM shown to be applicable to NEA data. Our main result is the determination of the thermal inertia of 5 NEAs, increasing the total number of NEAs with measured thermal inertia to 6. For two of our targets, previously available estimates are refined. Our results allow the first determination of the typical thermal inertia of NEAs, which is around 300 J s^{-1/2} K^{-1} m^{-2}, larger than the typical thermal inertia of large main-belt asteroids (MBAs) by more than an order of magnitude. In particular, thermal inertia appears to increase with decreasing asteroid diameter. Our results have been used by colleagues to estimate the size dependence of the Yarkovsky effect, thus explaining the apparent difference in the size-frequency distribution of NEAs and similarly sized MBAs. Thermal inertia is a very sensitive indicator for the presence or absence of particulate material on the surface. Our results indicate that even sub-km asteroids are covered with coarse regolith.
64 citations
"Near Earth Asteroids with measurabl..." refers background in this paper
...For instance, Golevka, Apollo, Toro, YORP, and Geographos are S/Q-type asteroids with an expected density between 2000 and 3000 kg/m3, while Ra-Shalom is a C-type so we expect a bulk density from 500 and 1500 kg/m3....
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...For Toro, Mueller (2012) reports a thermal inertia 200 Γ 1200 J m−2 s−0.5 K−1 but likely lower, which would result in a bulk density between 2000 and 4000 kg/m3....
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...Figure 9 shows the possible values of ρ as a function of Γ for asteroids Golevka, Apollo, Ra-Shalom, Toro, YORP, and Geographos....
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TL;DR: In this article, the authors used the lightcurve inversion method to model the shape and spin state of Geographos and obtained an excellent agreement between the model and observations, with the best-fit value υ = (1.15 ± 0.15) × 10 −8 rad d −2.
Abstract: Aims. The rotation state of small asteroids is affected by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) torque. The directly observable consequence of the YORP effect is the secular change of the asteroid’s rotation period. We carried out new photometric observations of asteroid (1620) Geographos in 2008 to extend the time line that, if long enough, would enable us to see possible deviations from a constant period rotation. Methods. We used the lightcurve inversion method to model the shape and spin state of Geographos. We assumed that the rotation rate evolves in time as ω(t) = ω0 + υt, where both the constant term of the rotation rate ω0 and the linear term υ are parameters to be optimized. In total, we used 94 lightcurves observed in 1969−2008. Results. We show that for υ = 0, a constant-period model, the whole dataset of lightcurves cannot be satisfactorily fitted. However, when relaxing υ in the optimization process we obtain an excellent agreement between the model and observations. The best-fit value υ = (1.15 ± 0.15) × 10 −8 rad d −2 implies that Geographos’ rotation rate accelerates by � 2. 7m s yr −1 . This is in agreement with the theoretically predicted value 1.4 × 10 −8 rad d −2 obtained from numerical integration of YORP torques acting on our convex shape model. Geographos is only the third asteroid (after (1862) Apollo and (54509) YORP) for which the YORP effect has been detected. It is also the largest object for which effects of thermal torques were revealed.
62 citations
Charles University in Prague1, University of Helsinki2, Jet Propulsion Laboratory3, University of Arizona4, University of Kharkiv5, Korea Astronomy and Space Science Institute6, University of Colorado Colorado Springs7, Academy of Sciences of Uzbekistan8, Keldysh Institute of Applied Mathematics9, Adam Mickiewicz University in Poznań10, University of Tokyo11
TL;DR: In this paper, the authors used the lightcurve inversion method to model the shape and spin state of Apollo and obtained a longer time line of the rotation period and its linear change in time.
Abstract: Aims. Asteroid (1862) Apollo is one of two asteroids in which the YORP effect was detected. We carried out new photometric observations of Apollo in April 2007 to enlarge the time line and to derive a more precise shape and spin state model. We also observed another YORP-candidate, asteroid (25143) Itokawa, in December 2006 and January 2007 to obtain a longer time line. An estimation of the YORP strength on Itokawa based on its precise shape model from the Hayabusa mission predicted the deceleration to be already observable during the 2007 apparition. Methods. We used the lightcurve inversion method to model the shape and spin state of Apollo. For Itokawa, the shape and pole direction are known to a high degree of accuracy from the Hayabusa mission, so we used a modified version of lightcurve inversion with only two free parameters – the rotation period and its linear change in time. Results. The new model of Apollo confirms earlier results. The observed acceleration of Apollo’s rotation rate is (5.5 ± 1.2) × 10 −8 rad d −2 , which is in agreement with the theoretically predicted value. For Itokawa, the theoretical YORP value is sensitive to the resolution of the shape model and lies in the range from − 2t o−3 × 10 −7 rad d −2 . This is inconsistent with results of lightcurve inversion that place an upper limit to the change of Itokawa’s rotation rate ∼1.5 × 10 −7 rad d −2 .
59 citations
TL;DR: In this article, the rotational and shape parameters of 50 asteroids were determined with a simultaneous least square fit on both the epochs and the amplitudes of the lightcurve data.
58 citations
TL;DR: In this article, the authors identify and quantified semi-major axis drifts in Near-Earth Asteroids (NEAs) by performing orbital fits to optical and radar astrometry of all numbered NEAs.
Abstract: We have identified and quantified semi-major axis drifts in Near-Earth Asteroids (NEAs) by performing orbital fits to optical and radar astrometry of all numbered NEAs. We focus on a subset of 54 NEAs that exhibit some of the most reliable and strongest drift rates. Our selection criteria include a Yarkovsky sensitivity metric that quantifies the detectability of semi-major axis drift in any given data set, a signal-to-noise metric, and orbital coverage requirements. In 42 cases, the observed drifts (~10^-3 AU/Myr) agree well with numerical estimates of Yarkovsky drifts. This agreement suggests that the Yarkovsky effect is the dominant non-gravitational process affecting these orbits, and allows us to derive constraints on asteroid physical properties. In 12 cases, the drifts exceed nominal Yarkovsky predictions, which could be due to inaccuracies in our knowledge of physical properties, faulty astrometry, or modeling errors. If these high rates cannot be ruled out by further observations or improvements in modeling, they would be indicative of the presence of an additional non-gravitational force, such as that resulting from a loss of mass of order a kilogram per second. We define the Yarkovsky efficiency f_Y as the ratio of the change in orbital energy to incident solar radiation energy, and we find that typical Yarkovsky efficiencies are ~10^-5.
57 citations