The Formation of Planets

Lecture by C.P. Dullemond

Institute for Theoretical Astrophysics

Heidelberg UniversityImage Credit: NASA

The Big Questions

After C. Mordasini

> 10 billion galaxies in the Universe

100 billion stars in eachgalaxy

several (?) planets aroundeach star

how many harbour life?

How did we come about?Are we alone in the Universe?

What is a planet?

Originally: „wandering star“The „star“ made trajectories with „epicycles“ across the sky

What is a planet?

Rocky planet:- Is round- Has solid surface- Sometimes an

atmosphere, too- In rare cases it has

liquid water- Consists mostly of rock

(silicates) in the outer parts and iron+nickel in the core

- All known rocky planets orbit a star

What is a planet?

Gas giant planet:- Is round- Has no solid surface- Presumably has rocky

core- Consist mostly of

Hydrogen and Helium- Mass >> Mearth- Most known gas giant

planets orbit a star- (Just this week the first

confirmed free-floating planet was announced: PSO J318.5-22)

What is a planet?

Ice giant planet:- Is round- Has no solid surface- Atmosphere is

Hydrogen and Helium- But interior is volatile

elements- Presumably has rocky

core too- Mearth < M < Mgasgp- All known ice giant

planets orbit a star

Immanuel Kant

Our Solar System

Why do all planets lie in the same plane?Why do they all have circular orbits?Why do they rotate all in the same direction?

Immanuel Kant and Pierre-Simon Laplacerealized that they must have formed from adisk around the young sun. Today we call thisthe „solar nebula“ or more general: a„protoplanetary disk“.

Today we know that protoplanetary disks exist

Today we know that protoplanetary disks exist

Constellation“Orion”

Today we know that protoplanetary disks exist

Constellation“Orion”

Today we know that protoplanetary disks exist

Today we know that protoplanetary disks exist

Hidden behind the far-end of the disk is the star

= 500 AU= 16x Distance Sun-Neptune

Today we know that protoplanetary disks exist

The ingredients of planet formation

Image Credit: NASA

Protoplanetary Disk

Dust (the raw material of rocky planets)

Comets (icy planetesimals)

Asteroids (rocky planetesimals)

Massive planets open up gaps in the disk(planet-disk interaction & disk hydrodyamics)

Planets grow through accretion of planetesimals

Dust coagulates to larger rocks, and eventually to planetesimals

Collisions are the driving process

Planets interact gravitationally: N-body dynamics

This lecture:

• ...focuses on the question „how did we come about?“, or more concretely: „how do planets form?“

• Active research area: Many of the main questions not yet solved.

• We will discuss the standard picture (for as much as a „standard picture“ exists at all)

• We will focus on physics• We will discuss mostly the formation of rocky

(earth like) planets, but also to some extent of gas giant planets.

Goals:

• Brief introduction to / reminder of:– Properties of the Solar System (the planets, asteroid belt, Kuiper belt,

comets, meteorites)

– Properties of Extrasolar Planetary Systems (methods of detection, current statistics)

– Glance over the standard model of planet formation

• Sharpening our tools:– Hydrodynamics and magnetohydrodynamics– Radiative transfer

Goals:

• Learn the physics of planet formation (part 1):– Protoplanetary disks (formation, structure, evolution, radiative transfer,

hydrodynamics, magnetohydrodynamics, turbulence, vortices, chemistry, planet-disk interaction)

– Growth of initial dust aggregates (“molecular” dynamics models, Smoluchowski equation: how to cover 40-orders of magnitude, processes: sticking, shattering, restructuring, porosity, evaporation/condensation, motion: drift, turbulence)

– Planetesimal formation (particle trapping, Roche density, Goldreich & Ward model, Kelvin-Helmholz turbulence, gravoturbulent PF, streaming instabilities)

– Restricted 3-body problem (Hill sphere, coorbital horseshoe region, Lagrange points, Jacobi integral, Tisserand relation, zero-velocity orbits, epicyclic motion, viscous stirring, chaos theory)

– Oligarchic growth of rocky planets (gravitational focusing, runaway growth, viscous stirring & dynamical friction, thermodynamic description, self-regulation leading to oligarchy)

– Mean motion resonances (resonant angles, libration, width of resonances, stability/instability)

Goals:

• Learn the physics of planet formation (part 2):– Internal structure of rocky bodies (gravitational compaction, internal

radioactive heating, differentiation, tectonics)

– Meteorite parent bodies (CAIs, chondrules, matrix, age determination)

– Gas giant planet formation (initial planetary core with acquired atmosphere, growth through accretion of planetesimals, collapse of atmosphere and runaway gas accretion, cooling problem, angular momentum problem, circumplanetary disk, origin of Saturn’s rings and giant planet moons)

– Planet-disk interaction & migration (spiral wave excitation and the resulting Lindblad torques, coorbital torques, saturation, role of disk viscosity, role of heating/cooling, gap opening, type I, II and III migration, migration as a “tool” to create hot Jupiters, to drive planets into resonances, migration traps)

– Planetary collisions (fully destructive collisions, hit-and-run collisions, mantel stripping, formation of binary and contact-binary bodies, mergers)

– Debris disks (collisional cascades, Poynting Robertsen drag, blow-out)

– Long-term dynamic evolution (the “Nice” model, Kozai cycles, stability)

Organization

• When: Each Monday, 14:15-16:00• Where: Philosophenweg 12, kleine Hörsaal• Web:

http://www.ita.uni-heidelberg.de/~dullemond/lectures/planetformation_2013/

• Moodle: via the web page (password=„Roche“)

• Registration: Please register on the Moodle, so that you are always up to date.

• Lecture material will be posted on the web page as much as possible. But some material may only be put on the Moodle (for copyright reasons).

Voluntary additional literature:

• Philip Armitage “Astrophysics of Planet Formation” (Cambridge University Press)– Lecture notes on which this book was based:

http://arxiv.org/abs/astro-ph/0701485v1

• The review ‘bibles’ of star and planet formation:– Protostars and Planets IV– Protostars and Planets V– Protostars and Planets VI. Book is not yet out.

Conference was in Heidelberg, July 2013. You can view the talks as movies:

http://www.mpia-hd.mpg.de/homes/ppvi/talks/

Other lecture material of interest:

• „Physics of accretion disks and planet formation“

by Christoph Mordasini (MPIA Heidelberg)

http://www.mpia-hd.mpg.de/homes/mordasini/lectureWS1112.html

• „Planetenentstehung“

by Willy Kley (University of Tübingen)

http://www.tat.physik.uni-tuebingen.de/~kley/lehre/planeten/index.html

Thanks to ...... for material

• Christoph Mordasini• Carsten Dominik• Willy Kley

The field of planet formation is quite an expansive field. I have received lots of very valuable information and material from the following people, to whom I am indebted:

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• Lecture „Astrobiologie und Astrobiophysik II“by Lisa Kaltenegger

Start: second week of this semester (next week)

Wednesdays, 17:15-18:45

INF 227, HS 2

Will cover lots of stuff about exoplanets!

Will be in German

Level = Bachelor