1. Observing Venus as a transiting exoplanet David Ehrenreich Astronomical School of Odessa

2. Image we detect a transiting Earth-size exoplanet within or near the habitable zone of its star. How ‘‘Earth-like’’ could it be? Could it be habitable? ?

3. Observing Venus as a transiting exoplanet David Ehrenreich Mathieu Barthélemy Jean Lilensten......................................IPAG, Grenoble Alfred Vidal-Madjar Alain Lecavelier des Etangs..........................IAP, Paris Thomas Widemann...........................LESIA, Meudon Guillaume Gronoff..............................NASA, Langley Paolo Tanga.................................................O CA, Nice Luc Arnold................................Obs. Haute- Provence David K. Sing..................................................U. Exeter exoplanet scientists + planetary scientists

4. Observing Venus as a transiting exoplanet Why do we want to do that? How do we do it? What results can we expect?

5. Observing planetary transits around other stars 1. Detect new exoplanets ✒ Batalha et al. (2012)

6. Observing planetary transits around other stars 2. Enable detailed physical & chemical studies ✒ Seager & Deming (2010)

7. Observing planetary transitsaround other stars

8. ‘‘hot Jupiter’’ HD 209458b (Rp/Rs)2(Rp/Rs)2 HST/STIS ✒ Brown et al. (2001) Relative flux Time from mid-transit (days) RsRs RpRp Observing planetary transitsaround other stars

9. ‘‘hot Jupiter’’ HD 209458b Relative flux Time from mid-transit (days) Observing planetary transitsaround other stars

10. Transit spectroscopy ✒ Fortney et al. (2010) Wavelength (µm) Radius (Jupiters) 2500K 500K

11. Jupiter-size ~ BRIGHT STARS ONLY Transit spectroscopy 100 to 1000 ppm

12. long-term goal ? Transit spectroscopy Habitability Biomarkers Life? composition: H, C+, O(?), Na, K, H 2 (?), H 2 O(??), CO 2 (???), CO, CH 4 (??), TiO(??), VO(??) + diffusion, hazes/clouds, winds, temperature inversions, evaporation, condensation, ionisation, chemical disequilibrium 2 prototypical hot Jupiters: HD209458b & HD189733b

13. 100 to 1000 ppm Jupiter-size ~ Atmospheric signal = f(transit depth, planet properties) Transit spectroscopy Earth-size ~ 0.1 to 1 ppm x10 geometrical effect ‘‘our’’ Venus from the Earth

14. Venus as a telluric exoplanet = An Earth-size planet close to the inner edge of the habitable zone of a bright solar-type star Time (h) Absorption (%) ✒ Schneider, Pasachoff & Willson 2006 Acrimsat ToV 2004

15. Transit of Venus An exoplanet perspective ≈1 R ♁ ➡ Can we detect the atmosphere of an Earth-size exoplanet? ➡ Is it habitable? ➡ Technique validation ➡ Proxy for future missions Transit of Venus 2004 (Trace) ✒ Pasachoff, Schneider & Widemann (2011)

16. Why? How? What? Observing Venus as a transiting exoplanet: How? Hubble Space Telescope GO#12537

18. ACS WFC3 STIS LRO Wide Angle Camera measuring the transit depth from 280 to 900 nm combination of filters & grisms

20. CO 2 -ν 3 Transit spectrum of Venus (prediction) 5000→| (+100 km) ✒ Kaltenegger & Traub 2009 ✒ Ehrenreich, Vidal-Madjar, Widemann et al. 2012, A&A Letters 537, L2

21. 10 wavelength (nm) altitude (km) 400 500600700 20 30 40 Rayleigh scattering (N 2 ) O2O2 O2O2 O3O3 OHP/Sophie (cloudy weather!) ✒ Vidal-Madjar et al. 2010 limb absorption target the penumbra during lunar eclipses model (no adjustments!) OHP Transit spectrum of the Earth (observed!)

22. Our last transit of Venus? An even more direct experiment Venus December 21 2012 Cassini/VIMS Nicholson et al.