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Astronomy 340 – Fall 2009

Lecture 21 19 Nov 2009

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Neptune migration

Neptune scatters planetesimals increase in eccentricity end up under the influence of J, S scattered out of solar sytem net fffect is that N scatters material inward and migrates outward.

Fernandez & Ip 1986

Tsiganis et al. 2005

Giant Planet Atmospheres and Spectra   Atomic/Molecular Abundances

  For a given temperature, pressure, composition model the Gibbs free energy

  H, He, Li, Na, K, Rb, Cs, Al, Ca, Fe, MgH, H2, CO, SiO, CH4,…

  Calculate mixing ratios

  Mixing fractions

Burrows & Orton 2009

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Giant Planet Atmospheres and Spectra   Calculate opacities   Assume LTE, estimate line strength

terms: gi – statistical weight of ith energy level fij – oscillator strength of ij transition Fi, Fj – excitation energies Q(T) – partition function of species at T = Σgie-hcF/kT S – strength in cm2 s-1 species-1

Continued…   Rayleigh scattering – most important in blue   Albedo, phase angle

  A little more complicated because light is reflected and emitted all in same part of spectrum

  Fp/Fstar = Ag(Rp/a)2 ϕ(α)   Last term is “phase function” – a combination of all the angles you can

think of   Ag = geometric albedo, reflectivity

  Derive a model light curve   Θ= true anomaly of planet

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Last steps…   Do the radiative transfer:

  dI/dm = opacity x (I –S)   Function of frequency and angle of propagation   I = specific intensity, S = source function

W = dilution factor (Rstar/a)2

Spiegel et al. 2009

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Evolution of the luminosity of giant planets

  Release of gravitational energy, release of internal energy (see eqn 7.13 in your book)

  L = 4πR2 σ(Te4-T0

4) = -d(McvTi)/dt   Te = actual effective temp.   T0 = temperature in absence of internal sources (starlight)   Ti = average internal temperature   Simplifies to τ= Mcv/4L young planets are much more

luminous

  Works well for Jupiter, not Saturn (additional heating from He settling?), not Uranus

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From Fortney et al (2009)