Overview of Planetesimal Accretion German-Japanese Workshop Jena, 01.10.2010 Chris W. Ormel Max-Planck-Institute for Astronomy, Heidelberg, Germany with Kees Dullemond, Hubert Klahr, Marco Spaans MPIA + U. of Heidelberg U. of Groningen
Contents Planet formation in context Gravitational focusing Runaway & oligarchy growth Timescales Role of debris Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 2/24
Observational constraints, context Mamajek (2009) Timescales for (gas) disk disappearance Several Myr Abundance of gas-giants in exo-systems Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 3/24
Solar system Eros NASA Allende, Carsten Münker Chris Ormel: planetesimal accretion Jena 01.10.2010 4/24
Particle motions 1mm Gas moves subkeplerian radial drift Radial drift ~10 m/s 10 m/s m-size barrier 1 m/s cg~105 cm/s Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 5/24 1cm 1m
Mass Gas runaway accretion 10 ME 100 km Runaway bodies separate Oligarchic growth/ Core formation Runaway growth km?? Plts. form mm/cm m? Plts. Source peters out @isolation mass Time Chris Ormel: planetesimal accretion Jena 01.10.2010 6/24
Planet formation Disk Instability Gas in the disk collapses e.g. Boss papers Core accretion Dust to planetesimals Planetesimals to protoplanets Protoplanet growth/migration (protoplanet interactions) Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 7/24
Accretion unknowns How are planetesimal bodies formed? Several barriers: bouncing, radial drift, fragmentation, charge (Güttler/Zsom et al. 2010; Brauer et al 2007; Birnstiel et al. 2009; Okuzumi 2009) Particle concentration through turbulence Johansen et al. 2007, 2009; Cuzzi et al 2008, 2010 Initial size, formation timescale Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 8/24
Gravitational focusing col = R2 Chris Ormel: planetesimal accretion Jena 01.10.2010 9/24
Viscous stirring (VS) Total motion Feedback effects growth Low random motions Increase vesc Increase VS vtot = vkepl + vran; vran ~evkepl Total motion Large random motions Chris Ormel: planetesimal accretion Jena 01.10.2010 10/24
GF velocity regimes Low v Intermediate/ Classical Rcol,max Co ll is i on v v a= ~vh rad iu s h ac o r p Ap y cit o l ve Large v, va Rgeo Random velocity, v (eccentricity) Hill velocity Chris Ormel: planetesimal accretion Jena 01.10.2010 11/24 Escape velocity, vesc
Runaway and oligarchic growth Normal growth Log (mass) Runaway growth Log (mass) 2 component distribution of oligarchs & Planetesimals (Kokubo & Ida 1998) Semi major axis Oligarchic growth mass (Color indicates eccentricity/random motion) Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 12/24
RG/Oligarchy: physical processes Dynamical Viscous stirring; Dynamical friction; Gas drag; Scattering; Physical Accretion Fragmentation Growth: increases vesc Stirring: increases vran Ormel et al. (2010a): Runaway growth: GFF increase Oligarchy: GFF decrease/stabilize Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 13/24
1 AU simulation (Ormel et al 2010b) Indicated are: Radius plts. (X) Position plts. (Y) Group total mass: Area dot~m1/3tot; mtot = Ng midv Grav. focusing factor w.r.t. biggest particle (v/vh, color) Single body (Ng = 1) Hill radius Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 14/24 vh: Hill velocity of largest body, vh~r1
Analysis Oligarchy Runaway growth Preconditions Dynamically cold disk All mass in planetesimals Runaway Growth GFF increases Growth timescales ~ same (fast!) Gra (inve vita rse tio ) nal FF Myr Size distribution Oligarchy GFF increases (levels off) Radius of biggest body (evolutionary parameter) Slower growth 2 component Equate timescales to solve Rtr (Ormel et al 2010a)... Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 15/24
Ormel et al. 2010a For R0 = 10 km Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 16/24
Mass Gas runaway accretion 10 ME 100 km Runaway bodies separate Oligarchic growth/ Core formation Runaway growth km?? Plts. form mm/cm m? Plts. Source peters out @isolation mass Time Chris Ormel: planetesimal accretion Jena 01.10.2010 17/24
Growth timescales in oligarchic reg. Oligarchic growth is slow Eccentricities (random motions) strongly increase Protoplanets heat food, before eating (Goldreich ea 2004) Gas damping equilibrium (large) GFF e.g., Kokubo & Ida (2002) Depends slightly on planetesimal size Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 18/24
Core formation Σ ~ 10 g/cm^2 (surface density plts) 1 Mearth 5 AU Veq, Tgrowth from Kokubo & Ida (2002) Chris Ormel: planetesimal accretion Jena 01.10.2010 19/24
Growth timescales in oligarchic reg. Oligarchic growth is slow Eccentricities (random motions) strongly increase Protoplanets heat food first, before eating Gas damping equilibrium (large) GFF e.g., Kokubo & Ida 2001 Scattering, gap formation Levison et al. (2010) Expect planetesimals to fragment Study accretion behavior of (small) fragments Paardekooper (2007); Johansen & Lacerda (2010); Kobayashi et al. (2010); Ormel & Klahr (2010) Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 20/24
Accretion of debris/fragments Factors: Pre-planetesimal population is small Fragments settle in thin plane May speed up growth (Kenyon & Bromley 2009) Radial drift Removes fragments Large gravitational focusing factors (???) Not necessarily Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 21/24
Gas flow around small protoplanet y (azimuthal) Drag force large for small particles Small particles coupled to (head)wind Fdrag ~ F2b No energy conservation (orbital decay) Chris Ormel: planetesimal accretion Jena 01.10.2010 22/24 Fsun F2b Fdrag x (radial)
Interactions w/ gas friction eg Rp=10km; s=1cm @1au Rp=103km; s=1cm @1au St: size of test particles, s ζw: size of planets, Rp Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 23/24 Rp=103km; s=1m @1au
Fragment accretion timescales Accretion timescales 5 AU, MMSN cold debris No depletion fragments No trapping particles No atmospheres No turbulence (wake) Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 24/24
Summary/Neglected effects Identified the runaway growth & oligarchy stages Formation 10 Mearth core remains difficult Fragmentation; gap formation/resonances; trapping Planetary atmosphere; migration of solids/planet Gravitational focusing boost growth Requires low random motions Role of the debris & gas-solid interaction Chris Ormel: Overview of planetary accretion models Jena 01.10.2010 25/24