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Planetesimal Growth and Planet Formation Planet Formation Planetesimal growth and Planetesimal growth and planet formation planet formation Anders Johansen Planet formation Planetesimals Streaming instability Metallicity Self-gravity Conclusions Anders Johansen (Leiden University! Lund) \Exoplanets Rising: Astronomy and Planetary Science at the Crossroads" Kavli Institute for Theoretical Physics, March{April 2010 Collaborators: Andrew Youdin, Thomas Henning, Hubert Klahr, Wlad Lyra, Mordecai-Mark Mac Low, Jeff Oishi Hydrodynamical models of planetesimal formation exhibit similar sharp dependence on metallicity Exoplanet-metallicity connection Planetesimal growth and planet First planet around (Gonzalez 1997; Santos et al. 2004; formation solar-type star found in Fischer & Valenti 2005) Anders Johansen 1995 (Mayor & Queloz 1995) Planet formation Today more than 400 Planetesimals exoplanets known Streaming instability ) Exoplanet probability Metallicity increases sharply with Self-gravity metallicity of host star Conclusions Exoplanet-metallicity connection Planetesimal growth and planet First planet around (Gonzalez 1997; Santos et al. 2004; formation solar-type star found in Fischer & Valenti 2005) Anders Johansen 1995 (Mayor & Queloz 1995) Planet formation Today more than 400 Planetesimals exoplanets known Streaming instability ) Exoplanet probability Metallicity increases sharply with Self-gravity metallicity of host star Conclusions Hydrodynamical models of planetesimal formation exhibit similar sharp dependence on metallicity ! ! ! ! . Planet formation Planetesimal Planetesimal hypothesis of Safronov 1969: growth and planet formation Planets form in protoplanetary discs from dust grains that collide Anders and stick together Johansen 1 Planet Dust to planetesimals formation µm ! cm: contact forces during collision lead to sticking Planetesimals cm ! km : ??? Streaming instability 2 Planetesimals to protoplanets Metallicity km ! 1,000 km: gravity Self-gravity 3 Protoplanets to planets 6 7 Conclusions Gas giants: 10 M⊕ core accretes gas (< 10 {10 years) Terrestrial planets: protoplanets collide (107{108 years) ! ! ! . Planet formation Planetesimal Planetesimal hypothesis of Safronov 1969: growth and planet formation Planets form in protoplanetary discs from dust grains that collide Anders and stick together Johansen 1 Planet Dust to planetesimals formation µm ! cm: contact forces during collision lead to sticking Planetesimals cm ! km : ??? Streaming instability 2 Planetesimals to protoplanets Metallicity km ! 1,000 km: gravity Self-gravity 3 Protoplanets to planets 6 7 Conclusions Gas giants: 10 M⊕ core accretes gas (< 10 {10 years) Terrestrial planets: protoplanets collide (107{108 years) ! ! ! Planet formation Planetesimal Planetesimal hypothesis of Safronov 1969: growth and planet formation Planets form in protoplanetary discs from dust grains that collide Anders and stick together Johansen 1 Planet Dust to planetesimals formation µm ! cm: contact forces during collision lead to sticking Planetesimals cm ! km : ??? Streaming instability 2 Planetesimals to protoplanets Metallicity km ! 1,000 km: gravity Self-gravity 3 Protoplanets to planets 6 7 Conclusions Gas giants: 10 M⊕ core accretes gas (< 10 {10 years) Terrestrial planets: protoplanets collide (107{108 years) ! ! . ! Planet formation Planetesimal Planetesimal hypothesis of Safronov 1969: growth and planet formation Planets form in protoplanetary discs from dust grains that collide Anders and stick together Johansen 1 Planet Dust to planetesimals formation µm ! cm: contact forces during collision lead to sticking Planetesimals cm ! km : ??? Streaming instability 2 Planetesimals to protoplanets Metallicity km ! 1,000 km: gravity Self-gravity 3 Protoplanets to planets 6 7 Conclusions Gas giants: 10 M⊕ core accretes gas (< 10 {10 years) Terrestrial planets: protoplanets collide (107{108 years) ! ! ! . Planet formation Planetesimal Planetesimal hypothesis of Safronov 1969: growth and planet formation Planets form in protoplanetary discs from dust grains that collide Anders and stick together Johansen 1 Planet Dust to planetesimals formation µm ! cm: contact forces during collision lead to sticking Planetesimals cm ! km : ??? Streaming instability 2 Planetesimals to protoplanets Metallicity km ! 1,000 km: gravity Self-gravity 3 Protoplanets to planets 6 7 Conclusions Gas giants: 10 M⊕ core accretes gas (< 10 {10 years) Terrestrial planets: protoplanets collide (107{108 years) ! ! ! ! . Planet formation Planetesimal Planetesimal hypothesis of Safronov 1969: growth and planet formation Planets form in protoplanetary discs from dust grains that collide Anders and stick together Johansen 1 Planet Dust to planetesimals formation µm ! cm: contact forces during collision lead to sticking Planetesimals cm ! km : ??? Streaming instability 2 Planetesimals to protoplanets Metallicity km ! 1,000 km: gravity Self-gravity 3 Protoplanets to planets 6 7 Conclusions Gas giants: 10 M⊕ core accretes gas (< 10 {10 years) Terrestrial planets: protoplanets collide (107{108 years) ! ! ! ! . Recipe for making planets? Planetesimal growth and (Paszun & Dominik) planet Hydrogen and Helium (98,5%) µm formation Anders Dust and ice (1,5%) Johansen Coagulation (dust growth) Planet formation ) Planets? Planetesimals Streaming instability Metallicity mm Self-gravity Conclusions (Blum & Wurm 2008) Recipe for making planets? Planetesimal growth and (Paszun & Dominik) planet Hydrogen and Helium (98,5%) µm formation Anders Dust and ice (1,5%) Johansen Coagulation (dust growth) Planet formation ) Planets? No Planetesimals Streaming instability Metallicity \Meter barrier": mm Self-gravity Growth to mm or cm, but not larger Conclusions The problem: small dust grains stick readily with each other { sand, pebbles and rocks do not (Blum & Wurm 2008) Overview of planets Planetesimal growth and planet Protoplanetary discs formation Anders Johansen Planet Dust grains formation Gas giants and Planetesimals ice giants Streaming instability Metallicity Self-gravity Pebbles Conclusions Terrestrial planets Dwarf planets+More than 400 exoplanets + Countless asteroids and Kuiper belt objects + Moons of giant planets Planetesimal formation must 1 proceed quickly 2 not rely on sticking between large solids 3 operate in a turbulent environment Planetesimals Planetesimal Kilometer-sized objects massive enough growth and planet to attract each other by gravity formation (two-body encounters) Anders Johansen Assembled from colliding dust grains Planet Building blocks of planets formation Planetesimals Problems: Streaming Pebbles, rocks and boulders: instability - drift rapidly through the disc William K. Hartmann Metallicity - have terrible sticking properties Self-gravity Conclusions Protoplanetary discs are turbulent Planetesimals Planetesimal Kilometer-sized objects massive enough growth and planet to attract each other by gravity formation (two-body encounters) Anders Johansen Assembled from colliding dust grains Planet Building blocks of planets formation Planetesimals Problems: Streaming Pebbles, rocks and boulders: instability - drift rapidly through the disc William K. Hartmann Metallicity - have terrible sticking properties Self-gravity Conclusions Protoplanetary discs are turbulent Planetesimal formation must 1 proceed quickly 2 not rely on sticking between large solids 3 operate in a turbulent environment Streaming instability Planetesimal growth and Youdin & Goodman 2005: (see also Goodman & Pindor 2000) planet formation Gas orbits slightly slower than Keplerian Anders Johansen Particles lose angular momentum due to headwind Planet Particle clumps locally reduce headwind and are fed by formation isolated particles Planetesimals Streaming instability Metallicity Self-gravity Conclusions v Kep (1− η ) F F GP Clumping Planetesimal Linear and non-linear evolution of radial drift flow of growth and planet meter-sized boulders: formation −1 −1 t=40.0 Ω t=80.0 Ω +20.0 +20.0 Anders Johansen +10.0 +10.0 ) ) r r Planet η +0.0 +0.0 η /( /( formation z z Planetesimals −10.0 −10.0 Streaming −20.0 −20.0 instability −20.0 −10.0 +0.0 +10.0 +20.0 −20.0 −10.0 +0.0 +10.0 +20.0 x/(ηr) x/(ηr) t=120.0 Ω−1 t=160.0 Ω−1 Metallicity +20.0 +20.0 Self-gravity +10.0 +10.0 Conclusions ) ) r r η +0.0 +0.0 η /( /( z z −10.0 −10.0 −20.0 −20.0 −20.0 −10.0 +0.0 +10.0 +20.0 −20.0 −10.0 +0.0 +10.0 +20.0 x/(ηr) x/(ηr) Strong clumping in non-linear state of the streaming instability (Youdin & Johansen 2007; Johansen & Youdin 2007; also Bai & Stone in preparation) Why clump? Planetesimal growth and planet formation Anders Johansen Planet formation Planetesimals Streaming instability Metallicity Self-gravity Conclusions Clumping in 3-D Planetesimal 3-D evolution of the streaming instability: growth and planet Particle size: formation 30 cm @ 5 AU or 1 cm @ 40 AU Anders Johansen Simulation box Disc Planet formation Planetesimals Streaming instability Metallicity Self-gravity Conclusions Particle clumps have up to 100 times the gas density Clumps dense enough to be gravitationally unstable But still too simplified: ) no vertical gravity and no self-gravity ) single-sized particles The streaming instability can provide the necessary ingredients for planetesimal formation Clumps readily contract gravitationally to form 100 km radius planetesimals Clumping depends on metallicity in a way that matches observed correlation between host star metallicity and exoplanets This talk Planetesimal growth and planet ) 3-D hydrodynamical simulations of particle sedimentation, formation Anders including multiple sizes, clumping
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