Planetesimal formation: when, where, how many?

Lund07-05-2015

collaboration:Kees DullemondFredrik WindmarkSatoshi Okuzumi

Joanna Drążkowska

Introduction

plan

ets!

Growth barriers

collisional radial drift● bouncing: mm- to cm-size● fragmentation: cm- to m-size

● m-size at 1 AUmm-size at 100 AU

Map of the growth barriers

Birnstiel+ 2012

drift dominatedfragmentation dominated

Ideas facilitating planetesimal formation

Pressure bump (+ sweep-up growth)

● Only <1% of dust particles are able to grow to planetesimal sizes

● Planetesimal formation only in the pressure bump

● Timescale of planetesimal growth: ~105 yrs

Drążkowska+ 2013, see also: Brauer+ 2008, Haghighipour 2005

Sweep-up growth triggered by the impact velocity distribution

Windmark+ 2012Garaud+ 2013

Drążkowska, Windmark & Okuzumi 2014

Sweep-up growth triggered by the impact velocity distribution

● Planetesimal formation is local and happens only inside of 1 AU● ~4% of dust turned to planetesimals● Growth is very fast, some planetesimals form in 100 yrs

Previous SI models: heavy hydrodynamical simulations with restricted size distributions

Streaming instability

● Planetesimal formation is only possible outside the snow line (due to the bouncing barrier)

Streaming instability

● Planetesimal formation requires enhanced metallicity and/or reduced pressure support => pressure bumps!

dust

-to-

gas

ratio

(pressure gradient)

Streaming instability

● It does never happen that 100%of dust is turned to planetesimals, typical value is 10%

Streaming instability

Drążkowska & Dullemond 2014

Summary

This picture is very different from what is used as the working hypothesis for planetesimal accretion and planet population synthesis models!

1. Drążkowska, Windmark & Dullemond 2013, A&A, 556, A37 2. Drążkowska, Windmark & Dullemond 2014, A&A, 567, A383. Drążkowska, Windmark & Okuzumi 2014, Proceedings of the IAUS 3104. Drążkowska & Dullemond 2014, A&A, 572, A78