1. Will exobiology out of the Solar System stop after the DARWIN mission ? Marc Ollivier (1), Alain Léger (1), Pascal Bordé (2) and Bruno Chazelas (1) (1) Institut d’Astrophysique Spatiale d’Orsay (2) IPAC - Caltech

2. VIRA - 20/21/22 March 2006 - PARIS - MO 2 DARWIN’s quest : first order spectroscopy …Pleurant, je voyais de l'or, - et ne pus boire. (A. Rimbaud)

3. VIRA - 20/21/22 March 2006 - PARIS - MO 3 1 What is the composition of the planetary atmosphere ? Is it primitive or did it evolve ? What about bio-markers ?

4. VIRA - 20/21/22 March 2006 - PARIS - MO 4 Infrared spectral range Selsis, ESA SP 518, 2002 H2OH2O CO 2 (50 mbar) CO 2 O3O3 CO NO 2 NO N2ON2O SO 2 CH 4 NH 3 65 CO 2 (1 bar) 2010 wavelength (  m) Resolution 10, 20, 10, 25 3, 20, 25 6 3, 20, 20 50 30 100 17 3, 3 4 4, 16, 19 4, 16, 19, 20, 20

5. VIRA - 20/21/22 March 2006 - PARIS - MO 5 Multi criteria spectral analysis Requires low res. spectra (r=20-50), moderate S/N Theory / observation : e.g. CO 2, H 2 O, O 3 (Selsis) Simultaneous presence of oxidizing / reducing gases (ex: CH 4 and O 2, NH 3 and O 2, ) (Sagan)

6. VIRA - 20/21/22 March 2006 - PARIS - MO 6 High resolution spectroscopy Specific spectral features at (r=200-500) e.g : technological gases Observation still at the planet scale S/N depending on the features Pb of contaminations by other species…

7. VIRA - 20/21/22 March 2006 - PARIS - MO 7 High resolution spectroscopy : how to ? Required spectral resolution : ~ 200 - 500 : DARWIN x 20 Required S/N : ~ 100 : DARWIN x 10 Signal = 10 ph / s / m 2 in [6-20  m] Assuming the same performance for the instrument (transmission, rejection, stability) Assuming integration times x 5 Collecting area x 400 i.e : diameter x 20 -> ELT in space -> Improvement in the instrument performance -> classical imaging + coronagraph -> other concept ?

8. VIRA - 20/21/22 March 2006 - PARIS - MO 8 High resolution spectroscopy : how to ? Angular résolution : 0.1 arcsec at 10  m -> 20-40 m class telescope Collecting area compatible High performance coronagraph Global efficiency x 10 at least No need for hyper telescope -> « BIG » NGST

9. VIRA - 20/21/22 March 2006 - PARIS - MO 9 2 What about the surface ? Are there evident traces of life activity on the planetary surface ? Can we image them ?

10. VIRA - 20/21/22 March 2006 - PARIS - MO 10 Direct imaging : hypotheses Image of an earthlike planet Planet distance : 10 pc : earth diameter = 8.5 10 -6 arcsec S/N = 10 per pixel Integration time : reasonable (?!) Collecting area : 20000 m 2 (equ. 10 x 50m telescope) Planet photon limited observations (100 pl. photons req) No planet rotation during exposure (or elementary exposure) Pb : day / night for the planet (phases) Visible spectral range 0.5 -> 1  m, mean wavelength 0.75  m : total flux in the spectral band : 0.1 ph / s / m 2 Efficiency of the detection chain (detector incl.) : 20 %

11. VIRA - 20/21/22 March 2006 - PARIS - MO 11 Direct imaging 16 x 16 -> 200 px Res = 4. 10 -7 arcsec -> 450 km Int. Time ~ 1 min - 3min

12. VIRA - 20/21/22 March 2006 - PARIS - MO 12 Direct imaging (2) 32 x 32 -> 800 px Res = 2. 10 -7 arcsec -> 900 km Int. Time ~ 3.5 min - 10 min

13. VIRA - 20/21/22 March 2006 - PARIS - MO 13 Direct imaging (3) 64 x 64 -> 3200 px Res = 10 -7 arcsec -> 1800 km Int. Time ~ 15 min - 45 min

14. VIRA - 20/21/22 March 2006 - PARIS - MO 14 Direct imaging (4) 128 x 128 -> 12800 px Res = 5.10 -8 arcsec -> 3600 km Int. Time ~ 1h - 3h

15. VIRA - 20/21/22 March 2006 - PARIS - MO 15 Direct imaging (5) 256 x 256 ->51200 px Res = 2.5 10 -8 arcsec -> 7200 km Int. Time ~ 3.5 h - 10h

16. VIRA - 20/21/22 March 2006 - PARIS - MO 16 Direct imaging (6) 512 x 512 ->204800 px Res = 1.2 10 -8 arcsec -> 15000 km Int. Time ~14 h - 40h

17. VIRA - 20/21/22 March 2006 - PARIS - MO 17 Direct imaging (7) 1024 x 1024 ->825000 px Res = 0.6 10 -8 arcsec -> 30000 km Int. Time ~ 2.3 days - 7 days

18. VIRA - 20/21/22 March 2006 - PARIS - MO 18 Direct imaging : conclusion Observation of the surface… OK at medium spatial resolution (200km/px) Observation of 10 km details: - about 1 week int time required (incl color information) - OK for fixed objects : towns, forests, seas, … - no hope to sea animals groups (except if they do not move) - (Still) more difficult if the planet rotates or if dark side is observed (except if strong artificial light)… -> need to increase drastically the collecting area weightless mirrors, increase of the launch capabilities, complex formation flying required -> reduction of the observation distance Observation probe

19. VIRA - 20/21/22 March 2006 - PARIS - MO 19 Weightless mirrors Polymer mirrors Gaseous mirrors (Laser Trapped mirrors)

20. VIRA - 20/21/22 March 2006 - PARIS - MO 20 3 Nearer better ?

21. VIRA - 20/21/22 March 2006 - PARIS - MO 21 A 10 pc trip ? Direct observation with a probe -> nearby observation –10 pc trip –Assuming c/10 (nuclear propulsion): about 300 years to reach the target –Single shot mission –No « direct » data transmission -> need to bring back the observation 300 years later. –Self flying mission –Strong risk of obsolescence…

22. VIRA - 20/21/22 March 2006 - PARIS - MO 22 4 Do we contact them ? The role of SETI

23. VIRA - 20/21/22 March 2006 - PARIS - MO 23 Conclusion DARWIN like missions are first but certainly most important steps providing strong clues for planetary composition and habitability Potential following missions should be HIGH RESOLUTION SPECTROSCOPY Direct imaging of the surface is difficult and maybe not relevant at low spatial resolution In situ exploration is a millennium project