The effect of the radial pressure gradient in protoplanetary disks on planetesimal formation

Xue Ning Bai, James McLellan Stone

Research output: Contribution to journalArticlepeer-review

111 Scopus citations


The streaming instability provides a promising mechanism for planetesimal formation because of its ability to concentrate solids into dense clumps. The degree of clumping strongly depends on the height-integrated solid to gas mass ratio Z in protoplanetary disks. In this Letter, we show that the magnitude of the radial pressure gradient that drives the streaming instability (characterized by Π = ηνK/cs, where ηvK is the reduction of Keplerian velocity due to the radial pressure gradient and c s is the sound speed) also strongly affects clumping. We present local two-dimensional hybrid numerical simulations of aerodynamically coupled particles and gas in the midplane of protoplanetary disks. Magnetic fields and particle self-gravity are ignored. We explore three different radial pressure gradient values appropriate for typical protoplanetary disks: Π = 0.025, 0.05, and 0.1. For each Π value, we consider four different particle size distributions ranging from submillimeter to meter sizes and run simulations with solid abundance from Z = 0.01 up to Z = 0.07. We find that a small radial pressure gradient strongly promotes particle clumping in that: (1) at fixed particle size distribution, the critical solid abundance Zcrit above which particle clumping occurs monotonically increases with Π and (2) at fixed Z, strong clumping can occur for smaller particles when Π is smaller. Therefore, we expect planetesimals to form preferentially in regions of protoplanetary disks with a small radial pressure gradient.

Original languageEnglish (US)
Pages (from-to)L220-L223
JournalAstrophysical Journal Letters
Issue number2 PART 2
StatePublished - Oct 20 2010

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Diffusion
  • Hydrodynamics
  • Instabilities
  • Planets and satellites: formation
  • Protoplanetary disks
  • Turbulence


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