Reflection Spectraof Giant PlanetsWith an Eye Towards TPF (and EPIC & ECLIPSE)

Jonathan J. FortneyMark S. MarleyNASA Ames Research Center

2005 Aspen Winter Conference onAstrophysics: Planet Formationand Detection

February 11, 2005

Burrows, et al. (2001)

If TPF-C planetarysystem targetswill be older than1 Gyr…

And if technical limitations will onlyallow characterization~1-5 AU from the parent star…

This constrains Teff < 400 K and gravity: 1 gSaturn - 10 gJupiter

for gas giants

EGP Characterization with an Eye Towards TPF-C

Teff < 400 K constrains expecteddominant chemical species:Carbon- CH4 Nitrogen- NH3 Oxygen- H2OExpected cloud species: H2O & NH3

T-P profiles forplanets in orbitaround the Sun

Tint=400K, 1 AUTint=250K, 3 AUTint=100K, 5 AU

The atmosphere codehas been used extensivelyto model the atmospheresof brown dwarfs and solarsystem planets

Fairly good agreement with Jupiter’s profile from Galileo Entry Probe

Our equilibrium chemistry ignores photochemically produced speciesthat control the heat balance in the Jupiter’s stratosphere.

Jupiter’sAtmospherefrom the GalileoEntry Probe

TOP: CH4 absorptioncoeffs. (Karkoschka,1994)

BOTTOM: Normalized Flux (at 0.5 µm),Observed vs. Model with solar abunds,no tweaked parameters or hazes.

JupiterModel

At long “visible” wavelengths, forthe hotter andyounger objects,thermal radiationdominates overreflected stellarlight

Stellar flux is our Sun

• TPF-C: 0.5 – 0.8 µm encompasses a very limited spectral region • Signature of clouds is clear (for instance, ratio of X0/X1 filters)• Longer wavelengths, to ~1.04 µm, includes thermal radiation at high Teff

• Standard Visible Filters: UBVRI • I-band reaches to 1.04 µm

• X2 filter also reaches thermal radiation near Teff ~ 400 K

What informationcan be obtainedfrom a few filters?

Are clouds andTeff detectable?

Color-Color Diagrams

BOLD=10X Jupiter gTHIN= Jupiter g

X2,V,I are an excellent Teff

diagnostic from400-250K, andfair from 100-250K.

V,X0,X1 are a diagnostic forclouds. B (~0.45 µm) is betterthan X0, but perhaps too short in λ

Conclusions

EGPs of ages > 1 Gyr, masses below ~ 10 MJ, d > 1 AU arelimited in Teff < 400K

• All visible spectra dominated by gaseous CH4 absorption• “Clear” (what about hazes?), H2O cloud dominated, and NH3

cloud dominated, are expected (Sudarsky, et al 2000)

Discerning clear from cloudy atmospheres can be done from 0.5 – 0.8 µm• This can be done with low-res spectra or a few filters• Determining Teff in this spectral range will be difficult

Determining Teff for cloudy planets (Teff< 400K) will be greatly helpedif TPF-C bandpass is extended to at least to ~1.04 µm

• CH4 band depths will help gauge EGP (and perhaps the planetary system’s?) metallicity• I have not yet in detail examined farther into the near IR, but that should be promising, due to the greater thermal radiation