Planetesimal growth and planet formation - growth and planet formation Anders Johansen Planet...

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Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Planetesimal growth andplanet formation

Anders Johansen (Leiden University Lund)

Exoplanets Rising: Astronomy and Planetary Science at the Crossroads

Kavli Institute for Theoretical Physics, MarchApril 2010

Collaborators: Andrew Youdin, Thomas Henning, Hubert Klahr, Wlad Lyra, Mordecai-Mark Mac Low, Jeff Oishi

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Exoplanet-metallicity connection

First planet aroundsolar-type star found in1995(Mayor & Queloz 1995)

Today more than 400exoplanets known

Exoplanet probabilityincreases sharply withmetallicity of host star

(Gonzalez 1997; Santos et al. 2004;Fischer & Valenti 2005)

Hydrodynamical models of planetesimalformation exhibit similar sharp dependence

on metallicity

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Exoplanet-metallicity connection

First planet aroundsolar-type star found in1995(Mayor & Queloz 1995)

Today more than 400exoplanets known

Exoplanet probabilityincreases sharply withmetallicity of host star

(Gonzalez 1997; Santos et al. 2004;Fischer & Valenti 2005)

Hydrodynamical models of planetesimalformation exhibit similar sharp dependence

on metallicity

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Planet formation

Planetesimal hypothesis of Safronov 1969:

Planets form in protoplanetary discs from dust grains that collideand stick together

1 Dust to planetesimalsm cm: contact forces during collision lead to stickingcm km : ???

2 Planetesimals to protoplanetskm 1,000 km: gravity

3 Protoplanets to planetsGas giants: 10 M core accretes gas (< 10

6107 years)Terrestrial planets: protoplanets collide (107108 years)

.

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Planet formation

Planetesimal hypothesis of Safronov 1969:

Planets form in protoplanetary discs from dust grains that collideand stick together

1 Dust to planetesimalsm cm: contact forces during collision lead to stickingcm km : ???

2 Planetesimals to protoplanetskm 1,000 km: gravity

3 Protoplanets to planetsGas giants: 10 M core accretes gas (< 10

6107 years)Terrestrial planets: protoplanets collide (107108 years)

.

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Planet formation

Planetesimal hypothesis of Safronov 1969:

Planets form in protoplanetary discs from dust grains that collideand stick together

1 Dust to planetesimalsm cm: contact forces during collision lead to stickingcm km : ???

2 Planetesimals to protoplanetskm 1,000 km: gravity

3 Protoplanets to planetsGas giants: 10 M core accretes gas (< 10

6107 years)Terrestrial planets: protoplanets collide (107108 years)

.

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Planet formation

Planetesimal hypothesis of Safronov 1969:

Planets form in protoplanetary discs from dust grains that collideand stick together

1 Dust to planetesimalsm cm: contact forces during collision lead to stickingcm km : ???

2 Planetesimals to protoplanetskm 1,000 km: gravity

3 Protoplanets to planetsGas giants: 10 M core accretes gas (< 10

6107 years)Terrestrial planets: protoplanets collide (107108 years)

.

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Planet formation

Planetesimal hypothesis of Safronov 1969:

Planets form in protoplanetary discs from dust grains that collideand stick together

1 Dust to planetesimalsm cm: contact forces during collision lead to stickingcm km : ???

2 Planetesimals to protoplanetskm 1,000 km: gravity

3 Protoplanets to planetsGas giants: 10 M core accretes gas (< 10

6107 years)Terrestrial planets: protoplanets collide (107108 years)

.

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Planet formation

Planetesimal hypothesis of Safronov 1969:

Planets form in protoplanetary discs from dust grains that collideand stick together

1 Dust to planetesimalsm cm: contact forces during collision lead to stickingcm km : ???

2 Planetesimals to protoplanetskm 1,000 km: gravity

3 Protoplanets to planetsGas giants: 10 M core accretes gas (< 10

6107 years)Terrestrial planets: protoplanets collide (107108 years)

.

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Recipe for making planets?

Hydrogen and Helium (98,5%)

Dust and ice (1,5%)

Coagulation (dust growth)

Planets?

(Paszun & Dominik)

(Blum & Wurm 2008)

m

mm

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Recipe for making planets?

Hydrogen and Helium (98,5%)

Dust and ice (1,5%)

Coagulation (dust growth)

Planets? No

Meter barrier:

Growth to mm or cm, but not larger

The problem: small dust grains stick

readily with each other sand,

pebbles and rocks do not

(Paszun & Dominik)

(Blum & Wurm 2008)

m

mm

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Overview of planets

Protoplanetary discs

Dust grains

Pebbles

Gas giants andice giants

Terrestrial planets

Dwarf planets+ More than 400 exoplanets+ Countless asteroids and Kuiper belt objects+ Moons of giant planets

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Planetesimals

Kilometer-sized objects massive enoughto attract each other by gravity(two-body encounters)

Assembled from colliding dust grains

Building blocks of planets

Problems:

Pebbles, rocks and boulders:

- drift rapidly through the disc- have terrible sticking properties

Protoplanetary discs are turbulent

William K. Hartmann

Planetesimal formation must

1 proceed quickly

2 not rely on sticking between large solids

3 operate in a turbulent environment

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Planetesimals

Kilometer-sized objects massive enoughto attract each other by gravity(two-body encounters)

Assembled from colliding dust grains

Building blocks of planets

Problems:

Pebbles, rocks and boulders:

- drift rapidly through the disc- have terrible sticking properties

Protoplanetary discs are turbulent

William K. Hartmann

Planetesimal formation must

1 proceed quickly

2 not rely on sticking between large solids

3 operate in a turbulent environment

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Streaming instability

Youdin & Goodman 2005: (see also Goodman & Pindor 2000)

Gas orbits slightly slower than Keplerian

Particles lose angular momentum due to headwind

Particle clumps locally reduce headwind and are fed byisolated particles

v (1 )Kep

FFG P

Planetesimalgrowth and

planetformation

AndersJohansen

Planetformation

Planetesimals

Streaminginstability

Metallicity

Self-gravity

Conclusions

Clumping

Linear and non-linear evolution