How to form planetesimals from mm-sized chondrules and chondrule aggregates

By D. Carrera, Anders Johansen, M. Davies. 2015

223 citations recorded by the source corpus.

The size distribution of asteroids and Kuiper belt objects in the solar system is difficult to reconcile with a bottom-up formation scenario due to the observed scarcity of objects smaller than $\sim$100 km in size. Instead, planetesimals appear to form top-down, with large $100-1000$ km bodies forming from the rapid gravitational collapse of dense clumps of small solid particles. In this paper we investigate the conditions under which solid particles can form dense clumps in a protoplanetary disk. We use a hydrodynamic code to model the interaction between solid particles and the gas inside a shearing box inside the disk, considering particle sizes from sub-millimeter-sized chondrules to meter-sized rocks. We find that particles down to millimeter sizes can form dense particle clouds through the run-away convergence of radial drift known as the streaming instability. We make a map of the range of conditions (strength of turbulence, particle mass-loading, disk mass, and distance to the star) which are prone to producing dense particle clumps. Finally, we estimate the distribution of collision speeds between mm-sized particles. We calculate the rate of sticking collisions and obtain a robust upper limit on the particle growth timescale of $\sim$$10^5$ years. This means that mm-sized chondrule aggregates can grow on a timescale much smaller than the disk accretion timescale ($\sim$$10^6 - 10^7$ years). Our results suggest a pathway from the mm-sized grains found in primitive meteorites to fully formed asteroids. We speculate that asteroids may form from a positive feedback loop in which coagualation leads to particle clumping driven by the streaming instability. This clumping, in turn reduces collision speeds and enhances coagulation.} Future simulations should model coagulation and the streaming instability together to explore this feedback loop further.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/aba0c451529d72df76c4323b20062dda14d6b264

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Citations in the corpus

SOAR TESS Survey. I. Sculpting of TESS Planetary Systems by Stellar Companions (2019, background): “These high-density regions can subsequently seed the formation of planetesimals (Carrera et al. 2015).”
Evidence for the formation of comet 67P/Churyumov-Gerasimenko through gravitational collapse of a bound clump of pebbles (2017, background): “The streaming instability is capable of concentrating dust particles with Stokes numbers around St ≈ 0.1 (Carrera et al. 2015; Yang et al. 2016).”
Close-in planetesimal formation by pile-up of drifting pebbles (2016, result): “Similar results were presented recently by Carrera et al. (2015), who also included dependence of the Zcrit on the Stokes number of particles.”
Planetesimal formation near the snowline: in or out? (2017, background): “Carrera et al. (2015) have investigated for what values of the solids-to-gas column density ratio streaming instability occurs, as function of the stopping time of the solid particles.”
The nature of the TRAPPIST-1 exoplanets. (2018, background): “…Birnstiel et al. 2012), 10-100 km-scale planetesimals form by a hydrodynamical instability (such as the streaming instability; (Youdin & Goodman 2005; Johansen et al. 2014)) in regions where the local solids-to-gas ratio is sufficiently high (Dra̧żkowska & Dullemond 2014; Carrera et al. 2015).”
THE MASS AND SIZE DISTRIBUTION OF PLANETESIMALS FORMED BY THE STREAMING INSTABILITY. I. THE ROLE OF SELF-GRAVITY (2015, methodology): “The streaming instability can produce strong clumping of solids across a wide region in the parameter space of metallicity, radial gas pressure gradient and particle size (Bai & Stone 2010c; Carrera et al. 2015).”
Planetesimal formation starts at the snow line (2017, methodology): “More recently, Carrera et al. (2015) and Yang et al. (2016) suggested that streaming instability is also possible for smaller grains, albeit at higher metallicity.”
Dust Evolution and the Formation of Planetesimals (2016, background): “Particle concentration by the streaming instability also appears problematic for mm-sized particles in the asteroid belt (Carrera et al. 2015).”
Fossilized condensation lines in the Solar System protoplanetary disk (2015, background): “, 2015) and they are also very inefficient in triggering the streaming instability (Youdin and Goodman, 2005; Bai and Stone, 2010a,b; Carrera et al., 2015).”
Pebble-isolation mass: Scaling law and implications for the formation of super-Earths and gas giants (2018, background): “However, an increased pebble-to-gas ratio will trigger the streaming instability (Bai & Stone 2010; Carrera et al. 2015), transforming the pebbles into planetesimals.”
Concentrating small particles in protoplanetary disks through the streaming instability (2016, methodology): “…we find that a grid of at least 512×512 with a simulation time of at least 400P is necessary to properly establish the saturation state of the solid concentration for particles of τs = 10−2, a condition which was not Article number, page 6 of 16 satisfied by the models of Carrera et al. (2015).”