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

Carrera, Daniel LU ; Johansen, Anders LU and Davies, Melvyn B LU (2015) In Astronomy & Astrophysics 579.
Abstract
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 similar to 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 used a hydrodynamic code to model the interaction between solid particles and the gas inside a shearing box inside the disk, considering particle sizes from submillimeter-sized chondrules to meter-sized rocks. We found that particles down... (More)
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 similar to 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 used a hydrodynamic code to model the interaction between solid particles and the gas inside a shearing box inside the disk, considering particle sizes from submillimeter-sized chondrules to meter-sized rocks. We found 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 made a map of the range of conditions (strength of turbulence, particle mass-loading, disk mass, and distance to the star) that are prone to producing dense particle clumps. Finally, we estimate the distribution of collision speeds between mm-sized particles. We calculated the rate of sticking collisions and obtain a robust upper limit on the particle growth timescale of similar to 10(5) years. This means that mm-sized chondrule aggregates can grow on a timescale much smaller than the disk accretion timescale (similar to 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. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
planets and satellites: terrestrial planets, asteroids: general, minor planets, planets and satellites: formation, protoplanetary disks, hydrodynamics, methods: numerical
in
Astronomy & Astrophysics
volume
579
publisher
EDP Sciences
external identifiers
  • wos:000358877100055
  • scopus:84933517385
ISSN
0004-6361
DOI
10.1051/0004-6361/201425120
language
English
LU publication?
yes
id
d7a28222-177a-4078-b758-6f0d83f9c66e (old id 7984934)
date added to LUP
2015-09-25 13:32:18
date last changed
2017-10-29 03:48:09
@article{d7a28222-177a-4078-b758-6f0d83f9c66e,
  abstract     = {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 similar to 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 used a hydrodynamic code to model the interaction between solid particles and the gas inside a shearing box inside the disk, considering particle sizes from submillimeter-sized chondrules to meter-sized rocks. We found 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 made a map of the range of conditions (strength of turbulence, particle mass-loading, disk mass, and distance to the star) that are prone to producing dense particle clumps. Finally, we estimate the distribution of collision speeds between mm-sized particles. We calculated the rate of sticking collisions and obtain a robust upper limit on the particle growth timescale of similar to 10(5) years. This means that mm-sized chondrule aggregates can grow on a timescale much smaller than the disk accretion timescale (similar to 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.},
  articleno    = {A43},
  author       = {Carrera, Daniel and Johansen, Anders and Davies, Melvyn B},
  issn         = {0004-6361},
  keyword      = {planets and satellites: terrestrial planets,asteroids: general,minor planets,planets and satellites: formation,protoplanetary disks,hydrodynamics,methods: numerical},
  language     = {eng},
  publisher    = {EDP Sciences},
  series       = {Astronomy & Astrophysics},
  title        = {How to form planetesimals from mm-sized chondrules and chondrule aggregates},
  url          = {http://dx.doi.org/10.1051/0004-6361/201425120},
  volume       = {579},
  year         = {2015},
}