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

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DARWIN’s quest : first order spectroscopy

…Pleurant, je voyais de l'or, - et ne pus boire.(A. Rimbaud)

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1What is the composition of the planetary atmosphere ?

Is it primitive or did it evolve ?What about bio-markers ?

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Infrared spectral range

Selsis, ESA SP 518, 2002

H2O

CO2

(50 mbar)

CO2

O3

CO

NO2

NO

N2O

SO2

CH4

NH3

6 5

CO2

(1 bar)

20 10wavelength (m)

Resolution10, 20, 10, 253, 20, 2563, 20, 205030100173, 344, 16, 194, 16, 19, 20, 20

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Multi criteria spectral analysis• Requires low res. spectra (r=20-50), moderate

S/N

• Theory / observation : e.g. CO2, H2O , O3 (Selsis)

• Simultaneous presence of oxidizing / reducing gases (ex: CH4 and O2, NH3 and O2,) (Sagan)

CH4 (10- 5 )

8

6

4

2

0

CH4 (1%)

8

6

4

2

0

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High resolution spectroscopy

• Specific spectral featuresat (r=200-500)e.g : technological gases • Observation still at the planetscale• S/N depending on the features • Pb of contaminations by other species…

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High resolution spectroscopy : how to ?• Required spectral resolution : ~ 200 - 500 : DARWIN x

20• Required S/N : ~ 100 : DARWIN x 10• Signal = 10 ph / s / m2 in [6-20m]

• 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 ?

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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

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2

What about the surface ?Are there evident traces of life activity on the planetary

surface ?Can we image them ?

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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 m2 (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 / m2

• Efficiency of the detection chain (detector incl.) : 20 %

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Direct imaging

16 x 16 -> 200 pxRes = 4. 10-7 arcsec -> 450 kmInt. Time ~ 1 min - 3min

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Direct imaging (2)

32 x 32 -> 800 pxRes = 2. 10-7 arcsec -> 900 kmInt. Time ~ 3.5 min - 10 min

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Direct imaging (3)

64 x 64 -> 3200 pxRes = 10-7 arcsec -> 1800 kmInt. Time ~ 15 min - 45 min

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Direct imaging (4)

128 x 128 -> 12800 pxRes = 5.10-8 arcsec -> 3600 kmInt. Time ~ 1h - 3h

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Direct imaging (5)

256 x 256 ->51200 pxRes = 2.5 10-8 arcsec -> 7200 kmInt. Time ~ 3.5 h - 10h

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Direct imaging (6)

512 x 512 ->204800 pxRes = 1.2 10-8 arcsec -> 15000 kmInt. Time ~14 h - 40h

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Direct imaging (7)

1024 x 1024 ->825000 pxRes = 0.6 10-8 arcsec -> 30000 kmInt. Time ~ 2.3 days - 7 days

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Direct imaging : conclusionObservation 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 sideis observed (except if strong artificial light)…-> need to increase drastically the collecting areaweightless mirrors, increase of the launch capabilities, complex formation flying required-> reduction of the observation distanceObservation probe

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Weightless mirrors• Polymer mirrors• Gaseous mirrors (Laser Trapped

mirrors)

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3Nearer better ?

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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…

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4Do we contact them ?

The role of SETI

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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