Observing Venus as a transiting exoplanet

1. Astronomical School of Odessa Observing Venusas a transiting exoplanet • David Ehrenreich

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 • DavidEhrenreich • MathieuBarthélemy • JeanLilensten......................................IPAG, Grenoble • AlfredVidal-Madjar • AlainLecavelier des Etangs..........................IAP, Paris • ThomasWidemann...........................LESIA, Meudon • GuillaumeGronoff..............................NASA, Langley • PaoloTanga.................................................OCA, Nice • LucArnold................................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 transitsaround other stars 1. Detect new exoplanets ✒ Batalha et al. (2012)

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

7. Observing planetary transitsaround other stars

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

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

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

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

12. Transit spectroscopy 2 prototypical hot Jupiters: HD209458b & HD189733b ? composition: H, C+, O(?), Na, K, H2(?), H2O(??), CO2(???), CO, CH4(??), TiO(??), VO(??) + diffusion, hazes/clouds, winds, temperature inversions, evaporation, condensation, ionisation, chemical disequilibrium long-term goal Habitability Biomarkers Life?

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

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 ToV 2004 Acrimsat Absorption (%) Time (h) ✒ Schneider, Pasachoff & Willson 2006

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

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

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

20. Transit spectrum of Venus (prediction) (+100 km) ✒ Kaltenegger & Traub 2009 CO2-ν3 5000→| ✒ Ehrenreich, Vidal-Madjar, Widemann et al. 2012, A&A Letters 537, L2

21. 40 O3 O2 O2 30 altitude (km) OHP/Sophie (cloudy weather!) 20 Rayleigh scattering (N2) 10 500 600 700 400 wavelength (nm) Transit spectrum of the Earth (observed!) limb absorption target the penumbra during lunar eclipses OHP ✒ Vidal-Madjar et al. 2010 model (no adjustments!)

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