Lecture “Planet Formation”
Topic:
Overview of
the standard model
of planet formation
Lecture by: C.P. Dullemond
Standard Model
1. A star is formed, surrounded by a disk of dust and gas
2. The dust particles coagulate forming ever larger dust
aggregates, rocks, boulders
3. ...some miracle happens... and sizes of >km are reached
(as we will see later, this is a strange thing)
4. These planetesimals gravitationally interact leading to
„runaway growth“. A „planetary embryo“ is formed (~
1000 km)
5. The embryo accretes further planetesimals and grows
6. Nearby embryos collide and merge to form a rocky planet
7. IF the planet continues to grow to ~ 10 Mearth, then it will
attract gas from the disk and form a gas giant planet.
Birthplace of stars: Molecular Clouds
Ophiuchus Giant Molecular Cloud (by Loke Tan)
Birthplace of stars: Molecular Clouds
Ophiuchus Giant Molecular Cloud (by Loke Tan)
Forming stars from Molecular Clouds
M. Bate
Exeter
UK
MOVIE
Very dense
Molecular
Cloud: very
aggressive
star formation
‘Isolated’ Star Formation
M.Hogerheijde1998, after Shu et al. 1987
Observed protoplanetary disks
Credit: NASA
Observed protoplanetary disks
HST image of AB Aurigae by Carol Grady
The long road from dust to planets
First growth phase
Final phase
Gravity
keeps/pulls
bodies
together
Aggregation
(=coagulation)
1m
1mm
1m
1km
Gas is
accreted
1000km
Covers 13 orders of magnitude in size = 40 (!!) orders of magnitude in mass
Immanuel Kant already understood it!
“Der Anfang der sich bildenden Planeten ist nicht allein in der
Newtonschen Anziehung zu suchen. Diese würde bei einem
Partikelchen von so ausnehmender Feinigkeit gar zu langsam
und schwach sein. Man würde vielmehr sagen, dass in diesem
Raume die erste Bildung durch den Zusammenlauf einiger
Elemente, die sich durch die gewöhnlichen Gesetze des
Zusammenhangs vereinigen, geschehe, bis derjenige Klumpen,
der daraus entstanden, nach und nach so weit angewachsen,
dass die Newtonsche Anziehungskraft an ihm vermögend
geworden, ihn durch seine Wirkung in die Ferne immer mehr zu
vergrößern.”
Aus: Immanuel Kant „Allgemeine Naturgschichte und Theorie des
Himmels“ (1755)
http://www.deutschestextarchiv.de/book/show/kant_naturgeschichte_1755
(thanks to Willy Kley for pointing me to this amazing citation)
Immanuel Kant already understood it!
“The start of the formation of a planet is not to be sought only in
the Newtonian attractive forces. They would, for such small
particles, be too slow and too weak. One would more say that the
first phases of growth take place through the collision of elements
that aggregate through the usual laws of cohesion, until these
clumps eventuell have grown so much, that the Newtonian
attractive forces, with their long range of influence, spur their
growth ever further.“
English translation from Immanuel Kant „Allgemeine
Naturgschichte und Theorie des Himmels“ (1755)
http://www.deutschestextarchiv.de/book/show/kant_naturgeschichte_1755
(thanks to Willy Kley for pointing me to this amazing citation)
So, what is this „cosmic dust“?
• Difficult to know because we have no method
(yet) of collecting interstellar dust
• But there is „interplanetary dust“ from evaporating
comets.
• These Interplanetary Dust Particles are dust
aggregates
Collected from the
stratosphere with
a U2 airplane
Particles move...
...because protoplanetary disks are turbulent, and turbulent gas stirs
up the dust.
...and because of drift (more on that during the lecture).
What happens when they collide?
Numerical models
Small sizes:
a = 10 μm
MOVIE
Paszun & Dominik 2009
See also Wada et al. 2009, Suyama, Wada & Tanaka 2008
What happens when they collide?
Laboratory experiments
MOVIE
From the laboratory
of J. Blum, Braunschweig
Movie from
NASA
Next phase: Growth by gravity
Thanks to Sean Raymond for lending me his movie
Next phase: Growth by gravity
MOVIE
Thanks to Sean Raymond for lending me his movie
Collision of two planets or moons
ARTIST IMPRESSION
Image credit:
Don Davis
Collision of two planets or moons
MOVIE
Asphaug & Reufer 2013
http://vimeo.com/50778094
Accretion of smaller bodies onto big ones
MOVIE
Stewart (2011)
http://www.fas.harvard.edu/~planets/sstewart/Movies.html
On to final planets
Figure from C. Mordasini‘s lecture
Formation of gas giants
(if sufficient gas is present)
Figure from C. Mordasini‘s lecture
Formation of gas giants
(if sufficient gas is present)
Artist‘s impression by
Moonrunner Design
National Geographic
http://science.nationalgeographic.com/science/wallpaper/planet-formation.html
Alternative GGP formation scenario
Gravitational instabilities in the disk
Model by
Thomas Quinn
http://www.psc.edu/science/quinn.html
Alternative GGP formation scenario
Gravitational instabilities in the disk
Model by
group of
Richard Durisen
http://hydro.astro.indiana.edu
Planet-disk interaction & migration
MOVIE
Kley & Nelson (2012) Annual Reviews of Astronomy & Astrophysics
http://vimeo.com/45256035
Planet formation synthesis models
MOVIE
Mordasini et al. (2009)