Transcript Fortney_JJF_Aspen2005

Reflection Spectra
of Giant Planets
With an Eye Towards TPF
(and EPIC & ECLIPSE)
Jonathan J. Fortney
Mark S. Marley
NASA Ames Research Center
2005 Aspen Winter Conference on
Astrophysics: Planet Formation
and Detection
February 11, 2005
EGP Characterization with an Eye Towards TPF-C
If TPF-C planetary
system targets
will be older than
1 Gyr…
And if technical
limitations will only
allow characterization
~1-5 AU from the
parent star…
This constrains
Teff < 400 K
and gravity:
1 gSaturn - 10 gJupiter
for gas giants
Burrows, et al. (2001)
T-P profiles for
planets in orbit
around the Sun
Tint=400K, 1 AU
Tint=250K, 3 AU
Tint=100K, 5 AU
Teff < 400 K constrains expected
dominant chemical species:
Carbon- CH4 Nitrogen- NH3 Oxygen- H2O
Expected cloud species: H2O & NH3
The atmosphere code
has been used extensively
to model the atmospheres
of brown dwarfs and solar
system planets
Jupiter’s
Atmosphere
from the Galileo
Entry Probe
Fairly good agreement with Jupiter’s profile from Galileo Entry Probe
Our equilibrium chemistry ignores photochemically produced species
that control the heat balance in the Jupiter’s stratosphere.
Jupiter
Model
TOP: CH4 absorption
coeffs. (Karkoschka,1994)
BOTTOM: Normalized Flux (at 0.5 µm),
Observed vs. Model with solar abunds,
no tweaked parameters or hazes.
At long “visible”
wavelengths, for
the hotter and
younger objects,
thermal radiation
dominates over
reflected stellar
light
Stellar flux is our Sun
What information
can be obtained
from a few filters?
Are clouds and
Teff detectable?
• 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
Color-Color Diagrams
BOLD=10X Jupiter g
THIN= Jupiter g
V,X0,X1 are a diagnostic for
clouds. B (~0.45 µm) is better
than X0, but perhaps too short in λ
X2,V,I are an
excellent Teff
diagnostic from
400-250K, and
fair from 100250K.
Conclusions
EGPs of ages > 1 Gyr, masses below ~ 10 MJ, d > 1 AU are
limited 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 helped
if 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