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Title: FROM DUST TO PLANETESIMAL: THE SNOWBALL PHASE?

Abstract

The standard model of planet formation considers an initial phase in which planetesimals form from a dust disk, followed by a phase of mutual planetesimal-planetesimal collisions, leading eventually to the formation of planetary embryos. However, there is a potential transition phase (which we call the 'snowball phase'), between the formation of the first planetesimals and the onset of mutual collisions amongst them, which has often been either ignored or underestimated in previous studies. In this snowball phase, isolated planetesimals move in Keplerian orbits and grow solely via the direct accretion of subcentimeter-sized dust entrained with the gas in the protoplanetary disk. Using a simplified model in which planetesimals are progressively produced from the dust, we consider the expected sizes to which the planetesimals can grow before mutual collisions commence and derive the dependence of this size on a number of critical parameters, including the degree of disk turbulence, the planetesimal size at birth, and the rate of planetesimal creation. For systems in which turbulence is weak and the planetesimals are created at a low rate and with relatively small birth size, we show that the snowball growth phase can be very important, allowing planetesimals to grow by a factor ofmore » 10{sup 6} in mass before mutual collisions take over. In such cases, the snowball growth phase can be the dominant mode to transfer mass from the dust to planetesimals. Moreover, such growth can take place within the typical lifetime of a protoplanetary gas disk. A noteworthy result is that, for a wide range of physically reasonable parameters, mutual collisions between planetesimals become significant when they reach sizes {approx}100 km, irrespective of their birth size. This could provide an alternative explanation for the turnover point in the size distribution of the present-day asteroid belt. For the specific case of close binaries such as {alpha} Centauri, the role of snowball growth could be even more important. Indeed, it provides a safe way for bodies to grow through the problematic {approx}1-50 km size range for which the perturbed environment of the binary can prevent mutual accretion of planetesimals. From a more general perspective, these preliminary results suggest that an efficient snowball growth phase provides a large amount of 'room at the bottom' for theories of planet formation.« less

Authors:
;  [1]; ;  [2];  [3]
  1. Department of Astronomy, Nanjing University, Nanjing, Jiangsu 210093 (China)
  2. Department of Astronomy, University of Florida, Gainesville, FL 32611-2055 (United States)
  3. Observatoire de Paris, Section de Meudon, F-92195 Meudon Principal Cedex (France)
Publication Date:
OSTI Identifier:
21474487
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 724; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/724/2/1153; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTEROIDS; DUSTS; MASS TRANSFER; ORBITS; PHASE TRANSFORMATIONS; PLANETS; PROTOPLANETS; SOLAR SYSTEM EVOLUTION; TURBULENCE; EVOLUTION

Citation Formats

Jiwei, Xie, Jilin, Zhou, Payne, Matthew J, Jian, Ge, and Thebault, Philippe. FROM DUST TO PLANETESIMAL: THE SNOWBALL PHASE?. United States: N. p., 2010. Web. doi:10.1088/0004-637X/724/2/1153.
Jiwei, Xie, Jilin, Zhou, Payne, Matthew J, Jian, Ge, & Thebault, Philippe. FROM DUST TO PLANETESIMAL: THE SNOWBALL PHASE?. United States. https://doi.org/10.1088/0004-637X/724/2/1153
Jiwei, Xie, Jilin, Zhou, Payne, Matthew J, Jian, Ge, and Thebault, Philippe. Wed . "FROM DUST TO PLANETESIMAL: THE SNOWBALL PHASE?". United States. https://doi.org/10.1088/0004-637X/724/2/1153.
@article{osti_21474487,
title = {FROM DUST TO PLANETESIMAL: THE SNOWBALL PHASE?},
author = {Jiwei, Xie and Jilin, Zhou and Payne, Matthew J and Jian, Ge and Thebault, Philippe},
abstractNote = {The standard model of planet formation considers an initial phase in which planetesimals form from a dust disk, followed by a phase of mutual planetesimal-planetesimal collisions, leading eventually to the formation of planetary embryos. However, there is a potential transition phase (which we call the 'snowball phase'), between the formation of the first planetesimals and the onset of mutual collisions amongst them, which has often been either ignored or underestimated in previous studies. In this snowball phase, isolated planetesimals move in Keplerian orbits and grow solely via the direct accretion of subcentimeter-sized dust entrained with the gas in the protoplanetary disk. Using a simplified model in which planetesimals are progressively produced from the dust, we consider the expected sizes to which the planetesimals can grow before mutual collisions commence and derive the dependence of this size on a number of critical parameters, including the degree of disk turbulence, the planetesimal size at birth, and the rate of planetesimal creation. For systems in which turbulence is weak and the planetesimals are created at a low rate and with relatively small birth size, we show that the snowball growth phase can be very important, allowing planetesimals to grow by a factor of 10{sup 6} in mass before mutual collisions take over. In such cases, the snowball growth phase can be the dominant mode to transfer mass from the dust to planetesimals. Moreover, such growth can take place within the typical lifetime of a protoplanetary gas disk. A noteworthy result is that, for a wide range of physically reasonable parameters, mutual collisions between planetesimals become significant when they reach sizes {approx}100 km, irrespective of their birth size. This could provide an alternative explanation for the turnover point in the size distribution of the present-day asteroid belt. For the specific case of close binaries such as {alpha} Centauri, the role of snowball growth could be even more important. Indeed, it provides a safe way for bodies to grow through the problematic {approx}1-50 km size range for which the perturbed environment of the binary can prevent mutual accretion of planetesimals. From a more general perspective, these preliminary results suggest that an efficient snowball growth phase provides a large amount of 'room at the bottom' for theories of planet formation.},
doi = {10.1088/0004-637X/724/2/1153},
url = {https://www.osti.gov/biblio/21474487}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 724,
place = {United States},
year = {2010},
month = {12}
}