Åke Nordlund Centre for Star and Planet Formation and Niels Bohr Institute University of Copenhagen.

Åke Nordlund

Centre for Star and Planet Formationand

Niels Bohr Institute

University of Copenhagen

Brown Dwarfs and Massive Planets What’s the difference?

Brown Dwarf Formation Turbulent fragmentation Interrupted accretion

Planet Formation Core accretion Gravitational instability Cosmochemical evidence new and severe constraints new paradigm for planet formation

Star formation (vastly better understood than planet formation!)

Formation of GMCs in the Galaxy de Avillez et al 2004-2010

Formation of MCs in GMc Kritsuk et al 2010

Formation of stars in MCs Padoan & Nordlund 2010

10003 cells, Mach 9 supersonic MHD-turbulencePadoan & Nordlund (2010)

Brown Dwarfs are marked with black dots, more massive

stars with white dots.

Brown Dwarfs are marked with black dots, more massive

stars with white dots.

Padoan, Kritsuk, Norman (2005)

Padoan, Kritsuk, Norman (2005)

Padoan, Kritsuk, Norman (2005)

Mass accreting from the ’envelope’ is not likely to be distributed in a smooth and

symmetric fashion

Mass accreting from the ’envelope’ is not likely to be distributed in a smooth and

symmetric fashion

Core Accretion Barely fast enough in the SS; Jupiter (and Saturn?)

Very difficult to explain Jupiter’s abundance pattern Much too slow at current Uranus & Neptune

Enter Nice model... Much too slow for wide orbit M-dwarf gas giants

Hello Nice? Excentric and non-coplanar orbits

?? Type I migration

arbitrary (and large) pre-factors

Current Paradigm: Start out with planetisimals + some remnant gas So, separation must have happened earlier!? Let’s back up to that time then:

Gas + dust in a disk Can gas and dust be separated? Yes, easily!

Just read Weidenshilling (1977) Unfortunately, the Sun devours the Z, leaves an X+Y disk

The CAI and AOA inclusions have condensed out of a dense, 26Al rich gas phase

The CAI and AOA inclusions have condensed out of a dense, 26Al rich gas phase

CAI = Calcium Aluminum InclusionsCAI = Calcium Aluminum Inclusions

AOA= Amoeboid Olivine AggregatesAOA= Amoeboid Olivine Aggregates

26Al is radio-active, with a 750.000 yr half-life Can be used as a very accurate clock, if initially uniform

It was present in the early Solar System Enough to melt bodies larger than about 50-100 km Need this bodies to form quickly!

It originates in ordinary supernovae Was transported to the early Solar System in a few Myr

Now (in press) has shown to be subjected to ”thermal processing” (T > 1500 K) in the early SS

From the reproducibility btw samples, the time scale of

formation of the first solids in the Solar System was

only a few thousand yrs!

From the reproducibility btw samples, the time scale of

formation of the first solids in the Solar System was

only a few thousand yrs!

27

The conclusion from this correlation is that 26Al was

initially homogeously distrubuted, but suffered

thermal processing

The conclusion from this correlation is that 26Al was

initially homogeously distrubuted, but suffered

thermal processing

Cf. Johansen & Lacerda (2010) ”Pebble accretion” onto planetesimals ”Doubles the mass in less than 150 years”

Cf. Johansen & Lacerda (2010) ”Pebble accretion” onto planetesimals ”Doubles the mass in less than 150 years”

Why should it stop there? Technical reasons:

Periodic box constrained growth (Johansen) Planetesimal Hill radius not resolved (Boley)

No physical reasons: Hill radius keeps growing: volume proportional to mass Unlike the end of run-away growth; excitation does not kill it

Gas - Fractionation

Migration

XYZ - Gravity

Z / XY - Separation

Z - Accretion

Gas - Accretion

XYZ - Gravity

Z - Accretion

Gas – Fractionation

Z / XY - Separation

Z - Accretion

Gas - Accretion Z / XY - Separation

Approximate log-spacing of plants Gregory (1715) Titius (1766) Bode (1772) Hayes & Tremain (1998) Poveda & Lara (2008) Lovis et al (2010)

Consider the no. of Hill radii ...

Spacings are clearly approximately logarithmic

(including in the SS), but the number of Hill radii seems

superficially to have nothing to do with it

Spacings are clearly approximately logarithmic

(including in the SS), but the number of Hill radii seems

superficially to have nothing to do with it

However, if the total (XY+Z) initial mass is used, all gaps are

similar, in terms of Hill radii!

However, if the total (XY+Z) initial mass is used, all gaps are

similar, in terms of Hill radii!

Brown Dwarfs can form the same way other stars form Turbulent fragmentation in cold molecular gas BD mass fragments are exceedingly numerous, but ... ... only a tiny fraction are dense enough to collapse into BDs Successful fragments are confined by very large dynamic

pressure (smooth convergence + shock)

Brown Dwarfs and Massive Planets Similar structure, but two modes of formation

direct, gravitational, by turbulent compression indirect, assisted by (rapid!) core formation

Some massive ’planets’ in excentric, non-aligned orbits may form through the indirect (BD-like) mode