1. Advantages and Strategies for Direct Imaging and Characterization of Exoplanets: 5-minute Summary
Wesley A. Traub
Jet Propulsion Laboratory, California Institute of Technology
The Search for Life in the Universe Symposium
STScI May 2009

2. Outline The Goals: Earths, Super-Earths, Search for Life
Detection: Transits, RV, Astrometry, Imaging
Characterization: Transit & Imaging Spectroscopy
Primary Transit
Secondary Transit
Direct Imaging

3. Observed vs Expected Planets
Corot, Kepler, (TESS): How many Earths & Super-Earths?
Ref.: (left) Extrasolar Planets Encyclopaedia (2009); (right) Multi-Planet Study (2009)

4. Astrometry & RV Can Find All Nearby Earths
HIP 1475
HIP 56997
HIP 67275
GAIA (70 µas)
1 m/s
TPF-C
(8 m) M2 K2 G2 F2
Planets ~Tidally Locked
Concentrate observing time (40% on a small number ~60 for SIM-Lite) over a 5 year mission.
To achieve sensitivity to 1 (1 AU) scaled to the luminosity of the star

5. Transits probably cannot characterize an Earth
Signal/Noise values:
Nearest examples:
Most probably transit will be at pc,
so 100 times fainter,
& 10 times smaller SNR
Primary Transit
Secondary Transit
Direct Imaging
Ref.: Kaltenegger & Traub 2009

6. Planets vs zodi: telescope size matters
HST 2.4-m
JWST 6.5-m
ATLAST 8-m
ATLAST 16-m
1.5 m
2.4 m
4 m
10 m
Ref.: (upper) M. Postman et al., ATLAST study; (lower) W. Cash et al., NWO study.

7. Habitability of an Earth-like Planet
Molecular
column
Mass
IR flux
IR color
Vis flux
Vis & IR
spectra
Eff temp.
Radius
Albedo
Greenhouse
warming
Density
of planet
Surface
gravity
Surface & cloud
reflectances
pressure
Scale height
of atmos.
Lapse rate
Temp.
TPF-C
TPF-C & TPF-I
TPF-I
SIM
measured
derived
Type of
planet
Likelihood of
plate tectonics &
atmos retention
Presence
of H2O
Cumulus,
cirrus, ice,
rock, sand,
water
implied

8. Species SNRs & abundance uncertainties
Bottom line:
An 8-m telescope can characterize nearby Earths,
and search for signs of life.
Ref.: M. Postman et al. 2009, ATLAST study.

9. Overall Summary Detection:
Transits will tell us the distribution function of Earths/Jupiters,
but not the addresses of the nearest Earths & Super-Earths.
Astrometry & RV can tell us the addresses of the nearest Earths.
Zodi:
We need to measure the zodi around nearby stars.
Characterization:
Transits will not characterize Earths or Super-Earths,
unless we are very lucky.
Direct optical imaging, with a large telescope, is needed to
characterize nearby Earths, and to search for signs of life on them.