The Formation of Planets
Lecture by C.P. Dullemond
Institute for Theoretical Astrophysics
Heidelberg University
Image Credit: NASA
The Big Questions
> 10 billion galaxies in the Universe
how many harbour life?
100 billion stars in each
galaxy
several (?) planets around
each star
How did we come about?
Are we alone in the Universe?
After C. Mordasini
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
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 Laplace
realized that they must have formed from a
disk around the young sun. Today we call this
the „solar nebula“ or more general: a
„protoplanetary disk“.
Immanuel Kant
Today we know that protoplanetary disks exist
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 farend of the disk is the star
= 500 AU
= 16x Distance Sun-Neptune
The ingredients of planet formation
Protoplanetary Disk
Comets (icy planetesimals)
Dust (the raw material
of rocky planets)
Planets grow through accretion
of planetesimals
Collisions are the driving process
Planets interact
gravitationally:
N-body dynamics
Asteroids (rocky planetesimals)
Dust coagulates to larger rocks,
and eventually to planetesimals
Massive planets open up gaps in the disk
(planet-disk interaction & disk hydrodyamics)
Image Credit: NASA
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.uniheidelberg.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
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:
• Christoph Mordasini
• Carsten Dominik
• Willy Kley
Advertisement:
• 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