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Observing Venus as a transiting exoplanet David Ehrenreich Astronomical School of Odessa Slide 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? ? Slide 3 Observing Venus as a transiting exoplanet David Ehrenreich Mathieu Barthlemy 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 Slide 4 Observing Venus as a transiting exoplanet Why do we want to do that? How do we do it? What results can we expect? Slide 5 Observing planetary transits around other stars 1. Detect new exoplanets Batalha et al. (2012) Slide 6 Observing planetary transits around other stars 2. Enable detailed physical & chemical studies Seager & Deming (2010) Slide 7 Observing planetary transitsaround other stars Slide 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 Slide 9 hot Jupiter HD 209458b Relative flux Time from mid-transit (days) Observing planetary transitsaround other stars Slide 10 Transit spectroscopy Fortney et al. (2010) Wavelength (m) Radius (Jupiters) 2500K 500K Slide 11 Jupiter-size ~ BRIGHT STARS ONLY Transit spectroscopy 100 to 1000 ppm Slide 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 Slide 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 Slide 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 Slide 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) Slide 16 Why? How? What? Observing Venus as a transiting exoplanet: How? Hubble Space Telescope GO#12537 Slide 17 Slide 18 ACS WFC3 STIS LRO Wide Angle Camera measuring the transit depth from 280 to 900 nm combination of filters & grisms Slide 19 Slide 20 CO 2 - 3 Transit spectrum of Venus (prediction) 5000| (+100 km) Kaltenegger & Traub 2009 Ehrenreich, Vidal-Madjar, Widemann et al. 2012, A&A Letters 537, L2 Slide 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!) Slide 22 Our last transit of Venus? An even more direct experiment Venus December 21 2012 Cassini/VIMS Nicholson et al. Slide 23