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Register a new userAsteroid migration due to the Yarkovsky effect and the distribution of the Eos family
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Yang-Bo Xu
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Based on a linearized model of the Yarkovsky effect, we investigate in this paper the dependence of the semimajor axis drift $Delta a$ of a celestial body on its size, spinning obliquity, initial orbit and thermal parameters on its surface. With appropriate simplification and approximation, we obtain the analytical solutions to the perturbation equations for the motion of asteroids influenced by the Yarkovsky effect, and they are then verified by numerical simulations of the full equations of motion. These solutions present explicitly the dependencies of $Delta a$ on the thermal and dynamical parameters of the asteroid. With these analytical formulae for $Delta a$, we investigate the combined seasonal and diurnal Yarkovsky effects. The critical points where the migration direction reverses are calculated and the consequent selective effects according to the size and rotation state of asteroids are discussed. %Solely the Yarkovsky effect is found to be able to produce some ring structure in the aged circumstellar debris disk. Finally, we apply the analytical formulae to calculate the migration of Eos family members. The space distribution of asteroids is well reproduced. Our calculations suggest that statistically the orientations of spin axes of family members satisfy a random-obliquity distribution, and the rotation rate $omega_{rm rot}$ of asteroid depends on its size $R$ by $omega_{rm rot}propto R^{-1}$.
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The Clarissa family is a small collisional family composed of primitive C-type asteroids. It is located in a dynamically stable zone of the inner asteroid belt. In this work we determine the formation age of the Clarissa family by modeling planetary perturbations as well as thermal drift of family members due to the Yarkovsky effect. Simulations were carried out using the Swift-rmvs4 integrator modified to account for the Yarkovsky and Yarkovsky-OKeefe-Radzievskii-Paddack (YORP) effects. We ran multiple simulations starting with different ejection velocity fields of fragments, varying proportion of initially retrograde spins, and also tested different Yarkovsky/YORP models. Our goal was to match the observed orbital structure of the Clarissa family which is notably asymmetrical in the proper semimajor axis. The best fits were obtained with the initial ejection velocities < ~20 m/s of diameter D=2 km fragments, 4:1 preference for spin-up by YORP, and assuming that 80% of small family members initially had retrograde rotation. The age of the Clarissa family was found to be 56+/-6 Myr for the assumed asteroid density 1.5 g/cm3. Small variation of density to smaller or larger value would lead to slightly younger or older age estimates. This is the first case where the Yarkovsky effect chronology has been successfully applied to an asteroid family younger than 100 Myr.
Any population of asteroids, like asteroid families, will disperse in semi-major axis due to the Yarkovsky effect. The amount of drift is modulated by the asteroid spin state evolution which determines the balance between the diurnal and seasonal Yarkovsky force. The asteroids spin state is, in turn, controlled in part by the YORP effect. The otherwise smooth evolution of an asteroid can be abruptly altered by collisions, which can cause impulsive changes in the spin state and can move the asteroid onto a different YORP track. In addition, collisions may also alter the YORP parameters by changing the superficial features and overall shape of the asteroid. Thus, the coupling between YORP and Yarkovsky is also strongly affected by the impact history of each body. To investigate this coupling we developed a statistical code modeling the time evolution of semi--major axis under YORP-Yarkovsky coupling. It includes the contributions of NYORP (normal YORP), TYORP (tangential YORP) and collisions whose effects are deterministically calculated and not added in a statistical way. We find that both collisions and TYORP increase the dispersion of a family in semi-major axis by making the spin axis evolution less smooth and regular. We show that the evolution of a familys structure with time is complex and collisions randomize the YORP evolution. In our test families we do not observe the formation of a YORP-eye in the semi-major axis vs. diameter distribution, even after a long period of time. If present, the YORP-eye might be a relic of an initial ejection velocity pattern of the collisional fragments.
Recent dynamical analyses suggest that some Jupiter family comets (JFCs) may originate in the main asteroid belt instead of the outer solar system. This possibility is particularly interesting given evidence that icy main-belt objects are known to be present in the Themis asteroid family. We report results from dynamical analyses specifically investigating the possibility that icy Themis family members could contribute to the observed population of JFCs. Numerical integrations show that such dynamical evolution is indeed possible via a combination of eccentricity excitation apparently driven by the nearby 2:1 mean-motion resonance with Jupiter, gravitational interactions with planets other than Jupiter, and the Yarkovsky effect. We estimate that, at any given time, there may be tens of objects from the Themis family on JFC-like orbits with the potential to mimic active JFCs from the outer solar system, although not all, or even any, may necessarily be observably active. We find that dynamically evolved Themis family objects on JFC-like orbits have semimajor axes between 3.15 au and 3.40 au for the vast majority of their time on such orbits, consistent with the strong role that the 2:1 mean-motion resonance with Jupiter likely plays in their dynamical evolution. We conclude that a contribution from the Themis family to the active JFC population is plausible, although further work is needed to better characterize this contribution.
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The Euphrosyne asteroid family occupies a unique zone in orbital element space around 3.15 au and may be an important source of the low-albedo near-Earth objects. The parent body of this family may have been one of the planetesimals that delivered water and organic materials onto the growing terrestrial planets. We aim to characterize the compositional properties as well as the dynamical properties of the family. We performed a systematic study to characterize the physical properties of the Euphrosyne family members via low-resolution spectroscopy using the IRTF telescope. In addition, we performed smoothed-particle hydrodynamics (SPH) simulations and N-body simulations to investigate the collisional origin, determine a realistic velocity field, study the orbital evolution, and constrain the age of the Euphrosyne family. Our spectroscopy survey shows that the family members exhibit a tight taxonomic distribution, suggesting a homogeneous composition of the parent body. Our SPH simulations are consistent with the Euphrosyne family having formed via a reaccumulation process instead of a cratering event. Finally, our N-body simulations indicate that the age of the family is 280 Myr +180/-80 Myr, which is younger than a previous estimate.
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