Transit spectrum of Venus as an exoplanet model prediction + HST programme Ehrenreich et al. 2012, A&A Letters 537, L2

Transit spectrum of Venus as an exoplanet model prediction + HST programme Ehrenreich et al. 2012, A&A Letters 537, L2 exoplanet scientist planetary scientist 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...OCA, Nice ESA/C. Carreau Luc Arnold...Obs. Haute-Provence David K. Sing...U. Exeter

Exoplanetary transit background source larger than the planet no spatial resolution

Exoplanetary transit hot jupiter HD 209458b Relative flux δ~1% HST/STIS Brown et al. 2001 Time from mid-transit (days) (R p /R? ) 2

Normalised flux Exoplanetary transit 883 nm 767 nm 758 nm 679 nm Phase (Sing et al. 2011) ( ) [R p ( )/R? ] 2 Transmission spectroscopy through the limb

Transit spectroscopy at the limb: 2 caveats Atmospheric limb properties averaged in latitude Sensitive to the highest absorbing species lower z cannot be probed

Atmospheric signal of a hot jupiter transit depth scale height k B T/µg (Δδ) atmo 2δ (H/R p ) n H Jupiter-size 0.01 to 0.1% 1% ~500 km

Atmospheric signal of a hot jupiter Relative flux difference during transit (%) HST/STIS Huitson et al. 2012 HD 189733b Na doublet Wavelength (Å)

Transmission spectrum HD 189733b Rp / R HST/STIS Huitson et al. 2012 STIS/G430L model w/ Rayleigh scattering by haze (Lecavelier et al. 2008) STIS/G750M STIS/G750M binned ACS Atmospheric scale heights model w/ solar Na abundance (Fortney et al.) Wavelength (Å) Haze scattering in exoplanetary atmosphere: a new challenge

Towards telluric planets 10! planet mean density Transits! Solar System! super-earths ice giants inflated giants Radius (Earths)! Transits 1! icy moons rocky moons Venus telluric planets water-rich Earth gas giants massive giants 0,1! 0,01! 0,1! 1! 10! 100! 1000! 10000! Radial velocities Mass (Earths)! rocky Kepler s smallest planets (only an upper limit to the mass)

Towards Earth-size planets near the habitable zone Confirmed transits vs. Kepler candidates (after 13 months in the mission) Borucki et al. 2011

Towards Earth-size planets near the habitable zone Kepler candidates 312 after 43 days 1,235 after 13 months 2,300+ after 16 months Batalha et al. 2012, submitted Most stars too faint for transit spectroscopy

Towards Earth-size planets Fressin et al. 2012 12.5-mag star K-20e δ = 82 ppm

Atmospheric signal of an Earth-size planet scale height k B T/µg (Δδ) atmo 2δ (H/R p ) n H Jupiter-size 0.01 0.1% 1% ~500 km Earth-size our Venus from the Earth 0.1 1 ppm 10 100 ppm~10 km x10 geometrical effect

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

Transit of Venus An exoplanet perspective Can we detect the atmosphere of an Earth-size exoplanet? Is it habitable? 1 R Proxy for future missions What atmospheric signatures can we expect? Transit of Venus 2004 (TRACE) Pasachoff, Schneider & Widemann 2011

Modelling the cytherean atmosphere cryosphere upper atmosphere mesosphere troposphere Pätzold et al. 2007 Gronoff et al. 2008 Cotton et al. 2011 Titov et al. 2009 de Bergh et al. 2006 Montmessin et al. 2011

Clouds & hazes cryosphere upper haze optically thick cloud deck

Upper haze of aerosols (70 90 km) Wilquet et al. 2009 mode-1 Altitude (km) mode-2 1 N (# cm -3 ) 10

Upper haze of aerosols (70 90 km) mode-2 particle size distribution particle size (µm) extinction cross section Mie extinction coefficient (cm -1 ) lognormal distribution Wavelength (µm) IDL Mie-extinction routines freely available@ http://www-atm.physics.ox.ac.uk/code/mie/index.html

Mie extinction absorption scattering Im(n) Re(n) 1 µm Wavelength (µm) 5 µm Hummel et al. 1988 Wilquet et al. 2009

Absorption & scattering Mie (modes 1+2) Mie (mode 1) CO2 Rayleigh

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

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

Transit spectrum of Venus (observed!) VTT observations during transit of Venus 2004 atmospheric limb Venus optically thick disc Transmission solar surface spectral dispersion Wavelength (nm) Hedelt et al. 2011

Venus as a transiting exoplanet Testing the model VTT observations during transit of Venus 2004 data (Hedelt et al. 2011) transit spectrum w/ mode-1+2 transit spectrum w/ mode-1

Next step towards a spatially unresolved, true exoplanet transit proxy w/ much larger wavelength range Hubble Space Telescope GO#12537 Ehrenreich, Vidal-Madjar, Arnold et al. Alfred Vidal-Madjar s talk