The Evolution of Earth-Approaching Binary Asteroids: A Monte Carlo Dynamical Model

doi:10.1006/icar.1995.1076

Icarus

Volume 115, Issue 1, May 1995, Pages 36-46

https://doi.org/10.1006/icar.1995.1076 Get rights and content

Abstract

We have developed a Monte Carlo model of the dynamical evolution of a binary asteroid crossing the Earth's orbit. At each close encounter with the Earth, the binary system undergoes impulsive variations of its orbital energy and angular momentum. Thus, after a great number of encounters, the system is dynamically evolved, and the two components may have either collided or escaped "to infinity." Tidal interactions between any two successive encounters also contribute to this dynamical evolution and change the original rotation rates of the components. We have carried out simulations of the evolution process under a variety of initial conditions and confirm that in general the characteristic evolution time is shorter than the typical lifetime of Earth-crossing asteroids vs collisions with the inner planets (≈ 100 Myr). The radar images obtained recently for several Earth-crossers reveal "bifurcated" structures which have been interpreted as contact binaries resulting from low-velocity collisions between two formerly separated components. In our scenario, such structures call be understood as resulting from dynamically evolved binary asteroids—although in the case of (4179) Toutatis the current rotation is so slow that it would require an unlikely cancellation of rotational and orbital angular momentum at the impact between the components. On the other hand, some other near-Earth objects with long rotation periods may be explained by tidal despinning within binary systems, followed by escape of the components. Moreover, collisions with the Earth of relatively young, well-separated binaries may explain the existence of doublet craters.

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Cited by (28)

The effect of planetary flybys on singly synchronous binary asteroids
2021, Icarus
Citation Excerpt :
In addition to the change in eccentricity, Collins et al. (2008) also derived the change in inclination. The change in energy of a perturbed binary system is studied by Farinella and Chauvineau (1993) and again in Chauvineua et al. (1995). Fang and Margot (2011) combined all these results and compared them to numerical simulations at a variety of encounter geometries.
The evolution of binary asteroid dynamics are not fully understood. The method of formation is widely accepted as spin-up and fission due to the YORP effect, but it is unclear why systems exist at a variety of energy levels. Binary asteroids are observed in states ranging from relaxed, synchronous equilibriums to chaotic dynamics. Previous planetary encounters may have an effect on the dynamic configuration of binary asteroids. We develop a model for the spherical restricted full three-body problem to simulate a binary asteroid perturbed by a planetary flyby, as well as a method of obtaining initial conditions for a relaxed, singly synchronous binary asteroid system. These are used in a numeric analysis employing a modified version of the General Use Binary Asteroid Simulator, where Monte Carlo simulations are leveraged to investigate how a range of Earth encounters affect the dynamic evolution of a generic binary asteroid system in a singly synchronous equilibrium. The results show that planetary flybys can disrupt the synchronous equilibrium, with the effects dropping off at far encounter distances and fast flyby speeds. After the impulsive perturbation of a planetary flyby, the binary asteroid spin-orbit coupling can prevent the system from settling into a new equilibrium, forcing the system to go through the energy dissipation process to re-equilibrate. It is therefore possible that planetary encounters may have a part in creating chaotic binary asteroid systems from previously relaxed equilibrated systems.
Morphology and population of binary asteroid impact craters
2013, Earth and Planetary Science Letters
Observational data show that in the Near Earth Asteroid (NEA) region 15% of asteroids are binary. However, the observed number of plausible doublet craters is 2–4% on Earth and 2–3% on Mars. This discrepancy between the percentage of binary asteroids and doublets on Earth and Mars may imply that not all binary systems form a clearly distinguishable doublet crater owing to insufficient separation between the binary components at the point of impact. We simulate the crater morphology formed in close binary asteroid impacts in a planetary environment and the range of possible crater morphologies includes: single (circular or elliptical) craters, overlapping (tear-drop or peanut shaped) craters, as well as clearly distinct, doublet craters. While the majority of binary asteroids impacting Earth or Mars should form a single, circular crater, about one in four are expected to form elongated or overlapping impact craters and one in six are expected to be doublets. This implies that doublets are formed in approximately 2% of all asteroid impacts on Earth and that elongated or overlapping binary impact craters are under-represented in the terrestrial crater record. The classification of a complete range of binary asteroid impact crater structures provides a template for binary asteroid impact crater morphologies, which can help in identifying planetary surface features observed by remote sensing.
Tidal interactions - Crude body model in dynamical investigations
2012, Planetary and Space Science
Citation Excerpt :
The phenomenon of tidal interactions was widely discussed in different models over last 160 years. Last decade of the XX century brought important papers which extensively explored the problem of tidal effects in a vicinity of planets (Chauvineau and Farinella, 1995; Bottke et al., 1999). Studies of small bodies dynamics in such region are usually made using the most complex physical body models which are able to give output in reasonable time scales.
The paper presents results of investigations of small bodies dynamics in a vicinity of giant planets. We used the most simple body model: gravitationally bounded, rotating contact binary affected by the tidal force acting from a planet. Spin variations of such binaries were extensively studied during planetary close encounters. Two main types of dynamical behaviour were observed: (i) huge but interim fluctuations of the angular velocity and (ii) permanent changes of a rotation during a close approach. The first type is observed mainly for fast rotators, while the second one was encountered in a population of slowly spinning objects with periods longer than 12 h. Conclusions on usability of such crude physical body models in dynamical investigations and a comparison to previous results were attached. The results allow us to formulate a thesis explaining the phenomenon of creation of the extremely slow rotators and an observational excess of such type of objects.
Binary asteroid systems: Tidal end states and estimates of material properties
2011, Icarus
Citation Excerpt :
Clearly, further research on the dynamical evolution of binary asteroid systems due to BYORP is required. In addition to BYORP, mass lofting could continuously expand the orbit (Harris et al., 2009; Fahnestock and Scheeres, 2009) while a close planetary encounter could impulsively expand the orbit and provide a moderate eccentricity (Chauvineau et al., 1995; Scheeres, 2007b). The short timescale for YORP spin-up could prevent some secondaries from synchronizing and may also be important in keeping the primary rotation rapid, hence fueling orbit expansion via mass lofting.
The locations of the fully despun, double synchronous end states of tidal evolution, where the rotation rates of both the primary and secondary components in a binary system synchronize with the mean motion about the center of mass, are derived for spherical components. For a given amount of scaled angular momentum J/J′, the tidal end states are over-plotted on a tidal evolution diagram in terms of mass ratio of the system and the component separation (semimajor axis in units of primary radii). Fully synchronous orbits may not exist for every combination of mass ratio and angular momentum; for example, equal-mass binary systems require J/J′ > 0.44. When fully synchronous orbits exist for prograde systems, tidal evolution naturally expands the orbit to the stable outer synchronous solution. The location of the unstable inner synchronous orbit is typically within two primary radii and often within the radius of the primary itself. With the exception of nearly equal-mass binaries, binary asteroid systems are in the midst of lengthy tidal evolutions, far from their fully synchronous tidal end states. Of those systems with unequal-mass components, few have even reached the stability limit that splits the fully synchronous orbit curves into unstable inner and stable outer solutions.
Calculations of material strength based on limiting the tidal evolution time to the age of the Solar System indicate that binary asteroids in the main belt with 100-km-scale primary components are consistent with being made of monolithic or fractured rock as expected for binaries likely formed from sub-catastrophic impacts in the early Solar System. To tidally evolve in their dynamical lifetime, near-Earth binaries with km-scale primaries or smaller created via a spin-up mechanism must be much weaker mechanically than their main-belt counterparts even if formed in the main belt prior to injection into the near-Earth region. Small main-belt binaries, those having primary components less than 10 km in diameter, could bridge the gap between the large main-belt binaries and the near-Earth binaries, as, depending on the age of the systems, small main-belt binaries could either be as strong as the large main-belt binaries or as weak as the near-Earth binaries. The inherent uncertainty in the age of a binary system is the leading source of error in calculation of material properties, capable of affecting the product of rigidity μ and tidal dissipation function Q by orders of magnitude. Several other issues affecting the calculation of μQ are considered, though these typically affect the calculation by no more than a factor of two. We also find indirect evidence within all three groups of binary asteroids that the semimajor axis of the mutual orbit in a binary system may evolve via another mechanism (or mechanisms) in addition to tides with the binary YORP effect being a likely candidate.
Radar observations and a physical model of contact binary Asteroid 4486 Mithra
2010, Icarus
Arecibo (2380 MHz, 12.6 cm) and Goldstone (8560 MHz, 3.5 cm) delay-Doppler radar images obtained in July and August of 2000 reveal that 4486 Mithra is an irregular, significantly bifurcated object, with a central valley ∼380 m deep and a long axis potentially exceeding 2 km. With its bimodal appearance, Mithra is a strong candidate for a contact binary asteroid. Sequences of Goldstone images spanning up to 3 h per day show very little rotation and establish that Mithra is an unusually slow rotator. We used Goldstone and Arecibo data to estimate Mithra’s 3D shape and spin state. We obtain prograde (λ = 337°, β = 19°) and retrograde (λ = 154°, β = −19°) models that give comparable fits, have very similar shapes roughly resembling an hourglass, and have a rotation period of 67.5 ± 6.0 h. The dimensions of these two models are very similar; for the prograde solution the maximum dimensions are X = 2.35 ± 0.15 km, Y = 1.65 ± 0.10 km, Z = 1.44 ± 0.10 km. Dynamical analysis of our models suggests that in the past, Mithra most likely went through a period of even slower rotation with its obliquity close to 90°. The spin rate is predicted to be increasing due to thermal torque (YORP), while the obliquity, which is currently +68° and +106° for the prograde and retrograde models, respectively, is predicted to move away from 90°.
Near-Earth Asteroid 2005 CR37: Radar images and photometry of a candidate contact binary
2006, Icarus
Citation Excerpt :
How did the shape of 2005 CR37 originate? Mechanisms thought capable of forming contact binaries include low-velocity collisions (Farinella, 1992; Hudson and Ostro, 1995; Chauvineau et al., 1995; Bottke and Melosh, 1996a, 1996b; Leinhardt et al., 2000), perhaps between components of true binaries, and spinup and shape distortion of gravitationally-bound agglomerates via either very close encounters with Earth and Venus (Asphaug and Benz, 1996; Richardson et al., 1998) or asymmetric solar absorption and re-emission (YORP; Bottke et al., 2002). Other explanations, such as a sequence of impacts that sculpted the object into its present shape, or an origin as an impact shard from catastrophic disruption of a larger progenitor, seem more contrived.
Arecibo (2380 MHz, 13 cm) radar observations of 2005 CR37 provide detailed images of a candidate contact binary: a 1.8-km-long, extremely bifurcated object. Although the asteroid's two lobes are round, there are regions of modest topographic relief, such as an elevated, 200-m-wide facet, that suggest that the lobes are geologically more complex than either coherent fragments or homogeneous rubble piles. Since January 1999, about 9% of NEAs larger than ∼200 m imaged by radar can be described as candidate contact binaries.

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Regular ArticleThe Evolution of Earth-Approaching Binary Asteroids: A Monte Carlo Dynamical Model

Abstract

Regular Article
The Evolution of Earth-Approaching Binary Asteroids: A Monte Carlo Dynamical Model