1 An emerging field: Molecules in Extrasolar Planets Jean Schneider - Paris Observatory ● Concepts and Methods ● First results ● Future perspectives

2 Concepts and Methods (1/13) ● What is a « planet »? ● Interest of molecules for exoplanetology ● How to detect molecules on a planet

3 Concepts and Methods (2/13) ● What is a « planet »? 1)A self-graviting object with no internal source of nuclear energy ==> M < 13 Jupiter mass (deuterium burning limit) ● Substellar companion to a parent star ● « Free floating » planet 2)An object formed in a circumstellar disc Approaches 1) and 2) coïncide approximately ● Type of planets: ● Giant, gazeous ● « Telluric », solid or liquid Present findings: ~ 170 giant planetary companions 1 free floating giant planet

4 Concepts and Methods (3/13) ● Interest for molecules – Diagnostics of planet physical parameters – Diversity in chemical composition – Exobiology

5 Concepts and Methods (4/13) ● Diagnostics of physical parameters ● Mass ● Radius ● Temperature ( mass, age) ● Albedo, opacities Reflection and thermal spectra

6 Concepts and Methods (5/13) ● An important difference with Solar System planets Many planets are very close to their parent star (up to 0.02 AU) Consequence: They are very strongly irradiated by their parent star ==> – Strong photochemistry – High planet temperature (up to 2000 K)

7 Concepts and Methods (6/13) ● Atmosphere models for giant planets. Similar to stellar atmosphere models + illumination by parent star Input parameters: – Effective temperature – Gravity (mass from age) – Input luminosity L – Abundances of chemical species – Line transition rates (up to 700 million molecular bands) – Complication: dust (SiO) Output: Planet spectra,

8 Concepts and Methods (7/13) CO, H 2 O, and CH 4 Opacities

9 Concepts and Methods (8/13) ● Examples of spectra K H20 CH4 H20 NH3 T = 1000 K log g = 4.5 Solar composition

10 Concepts and Methods (9/13) ● Examples of spectra as a function of stellar illumination (no dust)

11 Concepts and Methods (10/13) ● Interest for molecules Diversity in chemical composition==> eq. of state: – water planets – carbon planets (< 10 Earth mass)

12 Concepts and Methods (11/13) ● Interest for molecules – Exobiology: ● Molecules in the atmopshere: H20, oxygen, ozone, CH4 H2O: believed to be a pre-requisit for « life » - liquid ==> T~300K Oxygen (ozone): believed to be only a by-product of some photosynthesis: CH4: by-product of fermentation

13 Concepts and Methods (12/13) ● Interest for molecules – Exobiology: ● Molecules at the planet surface: chlorophyll (vegetation, plancton)

14 Concepts and Methods (13/13) ● How to detect molecules on a planet: – Transmission spectroscopy – Direct detection: Direct image Secondary eclipse Planet X From Star To Observer Parent star Planet

15 Very first results (1/4) ● GQ Lup Depth and shape of CO lines ==> log g = 2.52 Planckian spectrum ==> R = 2 Rjup ==> M = 2 MJup H2O CO 100 AU

16 Very first results (2/4) ● HD b – transmission spectra ==> First detection of a molecule on an exoplanet (Charbonneau et al. 2000) Na I

17 Very first results (3/4) ● HD b – transmission spectra

18 Very first results (4/4) ● Test of detectability of « chlorophyll » on an Earth-like exoplanet Veget. Red edge Arnold et al 2002 Globl spectrum of Earth seen as a single point Rayleigh scat.

19 Future perspectives Suspendend to the imaging capabilities of future instruments Problems: – Planets imbedded in the halo of their parent star due to: ● Atmospheric turbulence on the ground ● Stellar diffraction peak – Planet/star contrast very low: Solutions: – Suppress atmospheric turbulence with « Extreme » adaptive optics – Suppress stellar diffraction peak by some coronagraphic mask – Increase telescope size --> Interferometers

20 Future perspectives ● Reflection spectra of hot giant planets: – VLT-Planet Finder (coronagraphic camera at the VLT) – Pegase ? (1 km interferometric demonstrator in space – CNES) ● Reflection spectra of cold giant planets – Space coronagraphic telescopes: TPF-C (3 m X 7 m – NASA 2015) – Ground-based Extremely Large Telescopes (>30 m) ● Thermal spectra of giant planets – VLT-Planet Finder – Pegase ? ● Search for molecules of life on terrestrial planets: – Oxygen, ozone, CH4, H2O: TPF-C, Darwin/TPF-I (200 m IR interferom ) – Chlorophyll: TPF-C

21 Future perspectives ● Cartography of molecular distribution – Imaging of transiting planets (baseline 10 km at 1µ)

22 Future perspectives ● Cartography of molecular distribution – Multi-pixel spectral cartography (multi-thousand km interferometers 2025+) Everything about exoplanets: