Towards initial mass functions for asteroids and Kuiper Belt Objects

By J. Cuzzi, R. Hogan, William Bottke. 2010

143 citations recorded by the source corpus.

Abstract 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 millimeter-size particles. We sketch a scenario that might help explain how this occurred, in which primary accretion of 10–100 km size planetesimals proceeds directly, if sporadically, from aerodynamically-sorted millimeter-size particles (generically “chondrules”). These planetesimal sizes are in general agreement with the currently observed asteroid mass peak near 100 km 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 100 km 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 10–100 km 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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/866ab7b1f87fb65ac54f1f360b8f429e901fe5ae

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Citations in the corpus

The Compositional Structure of the Asteroid Belt (2015, background): “Smaller objects move more rapidly, where drift rates scale roughly as 1/D, which means that where we find smaller objects now may simply be a waypoint on a drift across the Asteroid Belt (where a 1 km body might drift roughly 10-4 AU in 1 Myr).”
The effect of gas drag on the growth of protoplanets. Analytical expressions for the accretion of small bodies in laminar disks (2010, background): “…less well to the gas and relative velocities increase, culminating in the so called metersize barrier, which, at our current level of understanding, can best be overcome by the combined efforts of turbulent concentration and gravitational collapse (Johansen et al. 2007, 2009; Cuzzi et al. 2010).”
In search of the source of asteroid (101955) Bennu: Applications of the stochastic YORP model (2015, background): “This parent body was created by planetesimal formation mechanisms that may have involved the turbulent concentration of very small bodies in the primordial solar nebula (e.g., Johansen et al., 2007, 2012; Cuzzi et al., 2010).”
Building Terrestrial Planets (2012, background): “However, the formation of self-gravitating clumps of small particles is sporadic (Chambers 2010, Cuzzi et al. 2010); hence, planetesimal formation can, in principle, proceed over an extended period of time.”
Primordial oxygen isotope reservoirs of the solar nebula recorded in chondrules in Acfer 094 carbonaceous chondrite (2011, background): “A limited amount of radial migration might occur between separated disk regions (Cuzzi et al., 2010), which resulted in limited range of the D17O values among relict olivine grains in many chondrules.”
FORMATION OF KUIPER BELT BINARIES BY GRAVITATIONAL COLLAPSE (2010, background): “Instead, asteroids have probably formed by the GI-related processes (Johansen et al. 2007, Cuzzi et al. 2010).”
26Al‐26Mg isotope systematics of the first solids in the early solar system (2013, unknown): “The relative ages of CAIs, AOAs, and chondrules inferred from the 26Al-26Mg chronometer thus provide important constraints on the models of the solar protoplanetary disk evolution (e.g., Ciesla 2010; Cuzzi et al. 2010).”
Fossilized condensation lines in the Solar System protoplanetary disk (2015, background): “Instead, modern accretion models (e.g. Johansen et al., 2007, 2015; Cuzzi et al., 2010) and the observed size distributions in the asteroid belt and the Kuiper belt suggest that planetesimals formed from self-gravitating clumps of small particles, with characteristics sizes of 100 km or larger (Morb”