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Young Jupiters are Faint. Jonathan Fortney (NASA Ames) Mark Marley (Ames) , Olenka Hubickyj (Ames/UCSC) , Peter Bodenheimer (UCSC) , Didier Saumon (LANL). Don Davis. Review evolution at young ages Nucleated collapse models (Core accretion – Gas capture) Alternate early evolution

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Young jupiters are faint
Young Jupiters are Faint

  • Jonathan Fortney (NASA Ames)

  • Mark Marley (Ames), Olenka Hubickyj (Ames/UCSC),

  • Peter Bodenheimer (UCSC), Didier Saumon (LANL)

Don Davis

“Arbitrarily Hot Start”

Teff (K)

log Age (Gyr)

Burrows et al. 2001

Early model evolution
Early Model Evolution

  • Initial conditions are uncertain

    • initial radii too large for smallest masses

    • collapse & accretion not spherical

  • “...assigning an age to objects younger than a few Myr is totally meaningless when the age is based on models using oversimplified initial conditions.” Baraffe et al. (2003)

  • When can the models be trusted?

  • Can initial conditions be improved?

Nucleated collapse model
Nucleated Collapse Model

  • Model for accretion of giant planets

    • 10 to 20 M⊕core forms first, initiates collapse of nebula

    • Time to gas runaway sensitively depends on atmospheric opacity

    • Peak accretion luminosity, created by shock, is short lived

    • Gives initial boundary condition for subsequent evolution

Hubickyj, Bodenheimer & Lissauer (2005)

How long is the formation time?

  • Opacity of proto-atmosphere affects formation time, as does surface density of the nebula

  • Only Podolak (2003) has tried to calculate the opacity of the proto-atmospheres during formation

  • When does t = 0?

  • Agreement with standard cooling models is even worse if one assigns t=0 to the post-formation time

Hubickyj, et al (2005)

A potential application 2m1207 companion
A Potential Application: 2M1207 Companion

  • Companion to ~M8 brown dwarf in TW Hydrae (age ~ 8 Myr)

  • red J-K implies late L, Teff ~ 1250 K

  • Models give M = 5 ± 2 MJup

Chauvin et al. (2004)

Teff (K)

log Age (Gyr)

Burrows et al. 1997

Similar problem for other objects
Similar Problem for Other Objects?

AB Dor C

Reiners et al. (2005) – young M star

Close et al. (2005) – young M star

Mohanty et al. (2004a,b)

Comparisons with hi-res spectra

Masses down to deuterium burning limit

Zapatero Osorio et al. (2004)

Dynamical masses of GJ 569 Bab brown dwarfs




  • Discern mass from g, Teff indicators in spectra & colors, not luminosity at young ages (This was just done for GQ Lup b)

  • (Of course, this isn’t always easy…)

log g = 5.5

log g = 4

from Knapp et al. (2004)

Which Bandpasses to Search?

Jupiter’s M band flux has stories to tell!

M band Jupiter image courtesy Glenn Orton


  • Luminosity of young giant planets depends sensitively on initial conditions

  • Nucleated collapse models are cooler, dimmer, and smaller than generic ‘hot start’ evolution calculations. Differences...

    • persist longer than “a few million years”

    • are more significant at larger masses

  • Use of ‘hot start’ evolution may result in substantially underestimating mass of observed objects, depending on actual formation mechanism