Lecture “Planet Formation”

Topic:

Overview of the standard modelof planet formation

Lecture by: C.P. Dullemond

Standard Model1. A star is formed, surrounded by a disk of dust and gas2. The dust particles coagulate forming ever larger dust

aggregates, rocks, boulders3. ...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 grows6. Nearby embryos collide and merge to form a rocky planet7. 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. BateExeterUK

Very dense Molecular Cloud: very aggressive star formation

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‘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

1m 1mm 1m 1km 1000km

Gravitykeeps/pulls

bodiestogether

Gas isaccreted

Aggregation(=coagulation)

First growth phase Final phase

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 thestratosphere with a U2 airplane

Particles move......because protoplanetary disks are turbulent, and turbulent gas stirsup the dust....and because of drift (more on that during the lecture).

What happens when they collide?

Paszun & Dominik 2009See also Wada et al. 2009, Suyama, Wada & Tanaka 2008

Small sizes:a = 10 μm

Numerical models

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What happens when they collide?Laboratory experiments

From the laboratoryof J. Blum, Braunschweig

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Movie fromNASA

Next phase: Growth by gravity

Thanks to Sean Raymond for lending me his movie

Next phase: Growth by gravity

Thanks to Sean Raymond for lending me his movie

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Collision of two planets or moons

Image credit:Don Davis

ARTIST IMPRESSION

Collision of two planets or moons

Asphaug & Reufer 2013http://vimeo.com/50778094

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Accretion of smaller bodies onto big ones

Stewart (2011)http://www.fas.harvard.edu/~planets/sstewart/Movies.html

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On to final planets

Figure from C. Mordasini‘s lecture

Formation of gas giants

Figure from C. Mordasini‘s lecture

(if sufficient gas is present)

Formation of gas giants(if sufficient gas is present)

Artist‘s impression byMoonrunner DesignNational Geographic

http://science.nationalgeographic.com/science/wallpaper/planet-formation.html

Alternative GGP formation scenarioGravitational instabilities in the disk

Model byThomas Quinn

http://www.psc.edu/science/quinn.html

Alternative GGP formation scenarioGravitational instabilities in the disk

Model bygroup ofRichard Durisen

http://hydro.astro.indiana.edu

Planet-disk interaction & migration

Kley & Nelson (2012) Annual Reviews of Astronomy & Astrophysicshttp://vimeo.com/45256035

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Planet formation synthesis models

Mordasini et al. (2009)

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