Formation of planetesimals from mm-sized grains Daniel Carrera - PowerPoint PPT Presentation

Formation of planetesimals from mm-sized grains Daniel Carrera Supervisors: Anders Johansen Melvyn B. Davies Lund Observatory, Sweden Carrera, D. , Johansen, A., & Davies, M. B. 2015, A&A, 579, A43 arXiv:1501.05314

Context: Giant planet formation (core accretion) Mass must grow x10 41 in ~3Myr. giant planets Bitsch+ 2015 accretion, migration Lambrechts+ 2014 pebble accretion planet cores Mustill+ 2015 Size ~ 10 M ⊕ dynamical evolution Carrera+ 2015 streaming instability planetesimals ~ 100 km mm - cm (Vesta) coagulation Disc Phase µ m Time 3 Myr

Streaming instability: Planetesimal formation planetesimal . . . (Vesta) 2009 simulation with particle size ~ 1 m Problem: ~1m bodies cannot form by coagulation Azimuthal direction Sun color = Σ solid Johansen+ (2009) Radial direction

Goals / Aims (1) What are the smallest particles that form particle clumps? R = ? (2) What are the conditions needed for the streaming instability? Streaming instability (i.e. planetesimals) Parameter Particle density sweep No streaming instability Particle size

Methods Protoplanetary Disk Star Pencil Code Brandenburg & Dobler (2002) Vertical direction ● Gas: 128 2 static grid ● Solids: particles 0 ● Box size: 0.2 H x 0.2 H ● Gas mass: 0.5 M earth ● Solid mass: 0.4 M moon Radial direction around the entire ring

Results (1) What are the smallest particles that form particle clumps? R = 1 – 4 mm (at 3 AU) (2) What are the conditions needed to form particle clumps? Carrera+ (2015) Clumping Streaming instability is active R = 1 – 4 mm at 3 AU No Σ solid No clumping Z = clumping Σ gas +Σ solid τ f = t f Ω kep Stopping time τ f = Orbital timescale No clumping Stokes number ( τ f )

Results / Application M disk , R particle , Z Planetesimal formation region Carrera+ (2015)

Summary (1) Jupiter has to form in ~3 Myr => planetesimals must form quickly. (2) When it works , the streaming instability can form planetesimals quickly. (3) We have found the conditions needed for the streaming instability. (4) We have shown that the streaming instability works for small particles (R ~ 1 – 4 mm at 3 AU) if the disc can concentrate particles well enough (Z ~ 0.04 – 0.07).

Extra slide 1: Resolution test Particle size: τ f = 0.003 / R ~ 2.5 mm τ f = 0.010 / R ~ 8 mm Resolution: 128 2 256 2 128 2 256 2 Simulation time ( t / Orbits ) Radial coordinate ( x / H )

Extra slide 2: Chondrule aggregates Ormel, Cuzzi, Tielens 2008 Aggregate Turbulence Size α = 10 -4 R ~ 1.2 mm α = 10 -6 R = 2-7 mm

Extra slide 3: Time between sticking collisions Time between sticking collisions: fraction of collisions that result in sticking relative speed − 1 t stick ≈ (σ v rel n F ) Particle with radius: r Collision cross section: number density cross section σ ~ π (2r) 2