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

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? ?

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

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

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

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

Observing planetary transitsaround other stars

‘‘hot Jupiter’’ HD b (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

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

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

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

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

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

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

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)

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

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

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

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

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