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Signatures of Life

Signatures of Life. Sara Seager Carnegie Institution of Washington. Signatures of Life. Spectra are required … … with observations from beyond Earth’s atmosphere Habitable exoplanets may already exist. atmosphere. habitability. L. Cook. surface. interior. Limits to Life on Earth.

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Signatures of Life

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  1. Signatures of Life Sara Seager Carnegie Institution of Washington

  2. Signatures of Life • Spectra are required … • … with observations from beyond Earth’s atmosphere • Habitable exoplanets may already exist

  3. atmosphere habitability L. Cook surface interior

  4. Limits to Life on Earth

  5. Life in the Universe All Life Chemical Energy Carbon-based Liquid water

  6. What is life? What does life do?

  7. Life Metabolizes

  8. Redox Reactions • All Earth life uses chemical energy generated from redox reactions • Life takes advantage of these spontaneous reactions that are kinetically inhibited

  9. Diversity of metabolisms rivals diversity of exoplanets Lane, Nature May 2006

  10. Chemical Energy Generation A huge amount of chemical energy is generated by photosynthesis from “light energy” Rosing 2005

  11. Earth Through Time Kasting Sci. Am. 2004 See Kaltenegger et al. 2006 Earth from the Moon Seager

  12. Signatures of Life • Spectra are required … • … from beyond Earth’s atmosphere • Habitable exoplanets may already exist

  13. Transiting Planet Science 10-3 10-4 10-2 Courtesy Lori Allen

  14. Transit Exoplanet Atmosphere Detection Scorecard

  15. Signatures of Life • Spectra are required … • … from beyond Earth’s atmosphere • Habitable may already exist

  16. Hot Super-Massive Earths • Ten exoplanets with Msini < 21 M • Short period • High chance to transit • What is their basic nature • Mini gas giants? • Ice giants? • Or rock giants?

  17. Exoplanet Bulk Composition • Transiting planets: densities will give exoplanet bulk composition • Large gas envelopes? • Ocean planets? • Silicate planets • Carbon planets … Seager, Kuchner, Hier-Majumder, Militzer

  18. Exoplanet Bulk Composition Current surveys MOST Corot/present RV Kepler/future RV Seager, Kuchner, Hier-Majumder, Militzer

  19. Exoplanet Bulk Composition Seager, Kuchner, Hier-Majumder, Militzer

  20. Generic Mass-Radius Relation Solid planets have a similar M-R relation EOSs of planetary materials are similar and approximately follow  = b+cPn. Seager, Kuchner, Hier-Majumder, Militzer

  21. Hot Super-Massive Earths • Ten exoplanets with Msini < 21 M • Short period • High chance to transit • Four orbit M stars • Tidally-locked • Day/night side -> hot/cold side?

  22. Atmospheric Circulation Venus • 1 day is almost the same as 1 year! (243 vs 225 days) • No day/night temperature gradient • Wind speed a few m/s up to 100s m/s

  23. Atmospheric Circulation Upsilon Andromedae b • Large thermal contrast at 24 m • We infer a global day-night temperature • and that the stellar energy is deposited high in the atmosphere R. Hurt/NASA/Caltech-JPL Harrington, Hansen, et al. 2006 Spitzer Space Telescope

  24. Habitable Zones on Tidally-Locked Exoplanets Planet diversity: • We expect the full range of planet day and night side temperatures! • Planets with hot/cold sides • Uniformly heated planets could be habitable 450-700K

  25. Liquid Water at High Pressure http://www.lsbu.ac.uk/water/phase.html

  26. Challenges to Life on Hot Exoplanets • Not necessarily the lack of liquid water • Kinetics may be too fast

  27. Signatures of Life • Spectra are required … • Metabolic byproducts cause chemical disequilibrium • … from beyond Earth’s atmosphere • Transit planet signal is smaller than changes in atmosphere • Theoretical limit to adaptive optics: 108 contrast • Telluric lines are a problem • Life on hot rocky exoplanets? • A range of T on tidally-locked super Earths • Liquid water can exist at high T and high P

  28. atmosphere habitability L. Cook surface interior

  29. Transit Planet Follow-up Lynnette Cook • Transit [Rp/R*]2 ~ 10-2 • Transit radius -> density • Emission spectra Tp/T*(Rp/R*)2 ~10-3 • Emitting atmosphere ~2/3 • Thermal phase curve • Temperature and T • Transmission spectra atm/R*2 ~10-4 • Upper atmosphere • Exosphere (0.05-0.15) • Reflection spectra p[Rp/a]2~10-5 • Albedo • Reflected light phase curve • Polarization • Scattering atmosphere Enabled by a differential measurement Seager et al. 2005 NASA/JPL-Caltech R. Hurt (SSC)

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