1. 1 Lecture 17: How to Find Life on Exoplanets: Biosignatures

2. 2 Finding „Pale Blue Dots“ 1) Our place in the universe: finding habitable planets 2) Search for Life No place like home... ?

3. 3 2) Search for life... - as we know it

4. 4 Signs Of Life On An Earth-like Planet Vegetation Plant product Plant life Bacteria observed Water Oxygen Carbon dioxide Methane Nitrous oxide Ozone Needed for life Primordial; & bacteria product

5. 5 Features: 1) observables & 2) unique ??

6. 6 Spectral features (example IR)

7. 7 Take-out on another planet?

8. 8 Planets NOW & EARTH... Part of the Puzzle

9. 9 HUGE HOT GAS BALL Atmosphere by transits...

10. 10 Spectrum for HD 189733b Obtained by transit transmission & eclipse emission Wavelength Inverse Residual Flux

11. 11 A 2  m Spectrum for HD 189733b (Swain et al. 2008)

12. 12 Earth ? EARTH – the next step

13. 13 Super-Earths: two families Rocky vs. Water

14. 14 Super-Earths geochemistry, e.g. the Carbonate-silicate cycle, or Sulfur cycle, etc. Planets of different initial conditions can be “driven” to a set of geochemical equilibria by global geo-cycles over geological timescales.

15. 15 Dominant Sulfur outgasing: with JWST Kaltenegger & Sasselov (2009) SO 2 CO 2 No O 2 or O 3, but N 2, CO 2, & CH 4.

16. 16

17. 17 Our Generation Explorers… find our path in unscarred territories Spitzer, Kepler, Darwin (ESA), Terrestrial Planet Finder (NASA)… Will answer a 1000s year old question… are there other pale blue dots out there? Alone ? Bacterial worlds ? Humans never evolve ? Exciting times ahead