Physical Properties of Near-Earth Objects

Binzel, Richard P.; Lupishko, D. F.; Martino, M. Di; Whiteley, Robert J.; Hahn, Gerhard

doi:10.2307/j.ctv1v7zdn4.24

Cited by 92 publications

(29 citation statements)

References 81 publications

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“…That is, while debate continues as to whether small amounts of melt might be found on the surfaces of many asteroids, which might be caused by impacts (e.g. Gaffey et al 1993Gaffey et al , 2002, only Vesta and a handful of other examples of fully melted basaltic objects have been found in spite of extensive searches (Binzel et al 2002;Moskovitz et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Toward Planetesimals: Dense Chondrule Clumps in the Protoplanetary Nebula

Cuzzi

Hogan

Shariff

2008

Astrophysical Journal

360

401

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We outline a scenario which traces a direct path from freely-floating nebula particles to the first 10-100km-sized bodies in the terrestrial planet region, producing planetesimals which have properties matching those of primitive meteorite parent bodies. We call this primary accretion. The scenario draws on elements of previous work, and introduces a new critical threshold for planetesimal formation. We presume the nebula to be weakly turbulent, which leads to dense concentrations of aerodynamically size-sorted particles having properties like those observed in chondrites. The fractional volume of the nebula occupied by these dense zones or clumps obeys a probability distribution as a function of their density, and the densest concentrations have particle mass density 100 times that of the gas. However, even these densest clumps are prevented by gas pressure from undergoing gravitational instability in the traditional sense (on a dynamical timescale). While in this state of arrested development, they are susceptible to disruption by the ram pressure of the differentially orbiting nebula gas. However, self-gravity can preserve sufficiently large and dense clumps from ram pressure disruption, allowing their entrained particles to sediment gently but inexorably towards their centers, producing 10-100 km "sandpile" planetesimals. Localized radial pressure fluctuations in the nebula, and interactions between differentially moving dense clumps, will also play a role that must be allowed for in future studies. The scenario is readily extended from meteorite parent bodies to primary accretion throughout the solar system.

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Section: Introductionmentioning

confidence: 99%

Toward Planetesimals: Dense Chondrule Clumps in the Protoplanetary Nebula

Cuzzi

Hogan

Shariff

2008

Astrophysical Journal

360

401

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“…Asteroids: Most of the S-type asteroids are probably related to ordinary (unmelted) chondrites (Binzel et al 2002, Clark et al 2002. This is not to say their interiors were never heated, or even partially melted (Elkins-Tanton and Weiss 2009) but there are only a few asteroid surfaces manifesting widespread and complete melting, as on Vesta.…”

Section: Introductionmentioning

confidence: 99%

Towards initial mass functions for asteroids and Kuiper Belt Objects

Cuzzi

Hogan

Bottke

2010

Icarus

160

195

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Our goal is to understand primary accretion of the first planetesimals. Some examples are seen today in the asteroid belt, providing the parent bodies for the primitive meteorites. The primitive meteorite record suggests that sizeable planetesimals formed over a period longer than a million years, each of which being composed entirely of an unusual, but homogeneous, mixture of mm-size particles. We sketch a scenario that might help explain how this occurred, in which primary accretion of 10-100km size planetesimals proceeds directly, if sporadically, from aerodynamically-sorted mm-size particles (generically "chondrules"). These planetesimal sizes are in general agreement with the currently observed asteroid mass peak near 100km diameter, which has been identified as a "fossil" property of the pre-erosion, pre-depletion population. We extend our primary accretion theory to make predictions for outer solar system planetesimals, which may also have a preferred size in the 100km diameter range. We estimate formation rates of planetesimals and explore parameter space to assess the conditions needed to match estimates of both asteroid and Kuiper Belt Object (KBO) formation rates. For parameters that satisfy observed mass accretion rates of Myr-old protoplanetary nebulae, the scenario is roughly consistent with not only the "fossil" sizes of the asteroids, and their estimated production rates, but also with the observed spread in formation ages of chondrules in a given chondrite, and with a tolerably small radial diffusive mixing during this time between formation and accretion. As previously noted, the model naturally helps explain the peculiar size distribution of chondrules within such objects. The optimum range of parameters, however, represents a higher gas density and fractional abundance of solids, and a smaller difference between keplerian and pressure-supported orbital velocities, than "canonical" models of the solar nebula. We discuss several potential explanations for these differences. The scenario also produces 10-100km diameter primary KBOs, and also requires an enhanced abundance of solids to match the mass production rate estimates for KBOs (and presumably the planetesimal precursors of the ice giants themselves). We discuss the advantages and plausibility of the scenario, outstanding issues, and future directions of research.

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“…Many scientists, e.g. Bottke et al (2002), Binzel et al (2002), and Weissman et al (2002), believe that asteroids are the main source of near-Earth objects (NEOs, i.e. objects with perihelion distance q<1.3 AU).…”

Section: Introductionmentioning

confidence: 99%

Comet and asteroid hazard to the terrestrial planets

Ипатов

Mather

2004

Advances in Space Research

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We estimated the rate of comet and asteroid collisions with the terrestrial planets by calculating the orbits of 13000 Jupiter-crossing objects (JCOs) and 1300 resonant asteroids and computing the probabilities of collisions based on random-phase approximations and the orbital elements sampled with a 500 yr step. The Bulirsh-Stoer and a symplectic orbit integrator gave similar results for orbital evolution, but may give different collision probabilities with the Sun. A small fraction of former JCOs reached orbits with aphelia inside Jupiter's orbit, and some reached Apollo orbits with semi-major axes less than 2 AU, Aten orbits, and inner-Earth orbits (with aphelia less than 0.983 AU) and remained there for millions of years. Though less than 0.1% of the total, these objects were responsible for most of the collision probability of former JCOs with Earth and Venus. We conclude that a significant fraction of near-Earth objects could be extinct comets that came from the trans-Neptunian region.

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Physical Properties of Near-Earth Objects

Cited by 92 publications

References 81 publications

Toward Planetesimals: Dense Chondrule Clumps in the Protoplanetary Nebula

Toward Planetesimals: Dense Chondrule Clumps in the Protoplanetary Nebula

Towards initial mass functions for asteroids and Kuiper Belt Objects

Comet and asteroid hazard to the terrestrial planets

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