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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

Young jupiters are faint

Young jupiters are faint

“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)

Young jupiters are faint

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)

Young jupiters are faint

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)

Young jupiters are faint

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