1. Exoplanet Studies / Terrestrial Planets in Habitable Zones Ed Turner Princeton University Observatory Institute for the Physics and Mathematics of the Universe, University of Tokyo March 27, : Beyond STScI

2. “I should disclose and publish to the world the occasion of discovering and observing four Planets, never seen from the beginning of the world up to our own times, their positions, and the observations about their movements and their changes of magnitude; and I summon all astronomers to apply themselves to examine and determine their periodic times ” --- Galileo Galilei (March 1610) on his discovery, in the previous year, of the moons of Jupiter.

3. Four hundred years after Galileo’s discoveries via the first astronomical use of the telescope, the world’s astronomers are once again using powerful new instrumentation to make startling discoveries of and about new planets, quite literally other worlds, which promise to once again transform our understanding of the nature of the Earth and of life’s and humanity’s places in the cosmos.

4. An Ancient and Fundamental Question
"There are infinite worlds both like and unlike this world of ours...We must believe that in all worlds there are living creatures and plants and other things we see in this world." Epicurus (c. 300 BCE)
"Do there exist many worlds, or is there but a single world? This is one of the most noble and exalted questions in the study of Nature." --- Albertus Magnus (d. 1280)
"To consider the Earth as the only populated world in infinite space is as absurd as to assert that in an entire field of millet, only one grain will grow."
---Metrodorus of Chios (4th century B.C.)

5. The Characterization Problem: Determine atmospheric and surface properties with special attention to “biosignatures”.
Venus
Earth
Mars

6. Atmospheric pressure and composition of Solar System planets

7. Visible reflection spectrum
H2O O3
Absorption spectra of O3, O2, H2O dominate.
Rayleigh scattering will add to spectrum.

9. The Earth’s Diurnal Light Curve
No Clouds: high contrast between land and ocean

10. THE RED EDGE

11. wavelength (m)

12. wavelength (m)

13. SETP before SETI?? “Trees are the Earth’s endless
effort to speak to the listening
heaven.”
Fireflies (1928)
Rabindranath Tagore

15. Polarized Signal in Diurnal Light Curve
Coastline
Coastline
Coastline
Forest/Jungle
Ocean
Desert
Ocean
Small
continent
Large continent

16. Where is the Habitable Zone?

17. The Kasting, Whitmire & Reynolds (1993) Habitable Zone - Now Iconic & Canonical

18. The Pioneering Sophisticated HZ Calculation by Kasting et al. 1993
1-D atmospheric/climate evolution model
Mean planetary albedo
Two stream greenhouse approximation
Atmospheric chemistry: CO2/H2O/N2
Water loss by photolysis & H escape (inner)
CO2 condensation  clouds, lapse rate (outer)
Stellar luminosity evolution (Continuous HZ)
Minimum biologically interesting HZ lifetimes
Tidal locking of planets in HZ of low mass stars

19. and obliquity “seasons”

20. NaCl Salinity Effects on Freezing Point of Water (at 1 atm*)
Pure water: 273 K = 0 C
Mean terrestrial seawater (3.5%): 271 K = -2 C
~3x seawater (10%): 267 K = -6 C
Dead** Sea (~30%): 245 K = -28 C
(90% more fixed cost, 42% cheaper for equal # of targets)
*Only slightly P sensitive over a wide range
**Not actually dead: very low concentrations of a few bacterial & fungi species normal “bloom” of Dunaliella (algae) & halobacteria following heavy winter rains.

21. HZ Time Domain Issues - Seasons
At constant illumination (ergs/s/cm2) Porb ~ M*17/8
Consider an Earth-twin planet
A 1.9 M A-star has Porb ≈ 4 yrs & 1 yr long seasons
A 0.5 M K-star has Porb ≈ 84 days & 3 wk long seasons
Interaction with thermal times scales of the atmosphere, ocean surface layers and large land masses very different

22. Can we begin to answer these questions via Galilean science (i. e
Can we begin to answer these questions via Galilean science (i.e., empirically):
Are there other worlds which resemble the Earth?
If so, how common are they?
How are they similar?
How are they different?
Are any of them life-bearing?
If so, what forms does alien life take, how similar to or different from terrestrial life?
YES WE CAN!