Escape of asteroids from the main belt

Abstract

Aims. We locate escape routes from the main asteroid belt, particularly into the near-Earth-object (NEO) region, and estimate the relative fluxes for different escape routes as a function of object size under the influence of the Yarkovsky semimajor-axis drift. Methods. We integrated the orbits of 78 355 known and 14 094 cloned main-belt objects and Cybele and Hilda asteroids (hereafter collectively called MBOs) for 100 Myr and recorded the characteristics of the escaping objects. The selected sample of MBOs with perihelion distance q > 1.3 au and semimajor axis a < 4.1 au is essentially complete, with an absolute magnitude limit ranging from H V < 15.9 in the inner belt (a < 2.5 au) to H V < 14.4 in the outer belt (2.5 au < a < 4.1 au). We modeled the semimajor-axis drift caused by the Yarkovsky force and assigned four different sizes (diameters of 0.1, 0.3, 1.0, and 3.0 km) and random spin obliquities (either 0 deg or 180 deg) for each test asteroid. Results. We find more than ten obvious escape routes from the asteroid belt to the NEO region, and they typically coincide with low-order mean-motion resonances with Jupiter and secular resonances. The locations of the escape routes are independent of the semimajor-axis drift rate and thus are also independent of the asteroid diameter. The locations of the escape routes are likewise unaffected when we added a model for Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) cycles coupled with secular evolution of the rotation pole as a result of the solar gravitational torque. A Yarkovsky-only model predicts a flux of asteroids entering the NEO region that is too high compared to the observationally constrained flux, and the discrepancy grows larger for smaller asteroids. A combined Yarkovsky and YORP model predicts a flux of small NEOs that is approximately a factor of 5 too low compared to an observationally constrained estimate. This suggests that the characteristic timescale of the YORP cycle is longer than our canonical YORP model predicts.

Infrared Spectroscopy of Large, Low‐Albedo Asteroids: Are Ceres and Themis Archetypes or Outliers?

“…Even if we consider the identifications of the compositions of Ceres and Themis to be unsettled, it is clear that there are important differences between their 3‐μm spectra and the CM meteorites and Ch asteroids, and those differences also can be seen among the eight large C‐complex asteroids we discuss and the meteorites. Objects are delivered to the near‐Earth object population from the entire asteroid belt, albeit with different efficiencies for different parts of the belt (Granvik et al, ). Given the relative abundance of these objects, it is not obvious why we should lack meteorites that are consistent with the Ceres and Themis types but have them from not only Pallas‐types but also, apparently, the high‐albedo objects >200 km (Vesta and howardite‐eucrite‐diogenite (HED) meteorites, and several S‐class asteroids and ordinary chondrites, mesosiderites, etc.…”

The Creston, California, meteorite fall and the origin of L chondrites

“…A model describing the evolution of small asteroids was developed that started with 92,449 test asteroids, distributed across the Main Belt (Granvik et al. , ). Of these, 70,708 evolved into NEO orbits.…”

“…In Main Belt, based only on size: possibly underestimated by factor of 3-5 (see text). developed that started with 92,449 test asteroids, distributed across the Main Belt (Granvik et al 2016(Granvik et al , 2017. Of these, 70,708 evolved into NEO orbits.…”

A Dark Asteroid Family in the Phocaea Region

“…Moreover, the Granvik et al (2016Granvik et al ( , 2017 NEO model predicts that the number of NEOs with 17 < H < 22 originating in the Phocaea region should be about 670, which represents about 3% of the entire NEO population. This is comparable to the fraction of objects originating in the outer main belt with a > 3 au (3.5%) and the Jupiter-family comets (2%).…”