Earth's transmission spectrum from lunar eclipse observations

Transcription

1 Earth's transmission spectrum from lunar eclipse observations Pallé et al. 009, Nat. E. Palle, M.R. Zapatero-Osorio, R. Barrena, P. Montañes-Rodriguez, E. Martin, A. Garcia-Muñoz

2 Nowadays we can monitor night lights, atmospheric changes, plankton blooms, forest health, etc...

3 But, how does our planet look like to ET?

4 When observing an exoplanet, all the light will come from a single point. We will need a detailed understanding of the micro-scale processes to interpret the observed macro-scale properties

5 Observing the Earth as a planet (no spatial resolution) Earth as-a-point observations with a very remote sensor A compilation of high spatial resolution data into a global spectra or photometry, and modeling Earthshine Observations: The Earthshine is the ghostly glow on the dark side of the Moon

6 The Earthshine on the moon ES/MS = albedo (+ geometry and moon properties)

7 Leonardo da Vinci, Codex Leicester, 1510

8 Spectral Albedo of the Earth: 003/11/19 Rayleigh Scattering Chappuis Ozone band BA-O Vegetation O Atmospheric Water vapor Montañés-Rodriguez et al., ApJ, 006

9 But isolating the light from the planet is VERY challenging, what if direct detection is not possible? Atmospheric characterization of Hot Jupiters has already been achieved trough transit spectroscopy What about transiting Earths?

10 We can observe it during a lunar eclipse NOT, Visible, μm WHT, Near-IR, μm La Palma, Canaries

11 Lunar eclipse August 16th 008

12 Umbra Penumbra Brigth Moon

13 Umbra/Bright Umbra Bright Hα

14 Earth s Transmission Spectrum The pale red dot μm

15 Earth s Transmission Spectrum Visible HO Ca II 3 O μm O 0.9

16 Fraunhofer lines structure 4 Ca II NO? O α H Ca II

17 Earth s Transmission Spectrum Near-IR ZJ O O O O O 1.0 CO O N HO μm

18 Atmospheric Dimers: Van de Waals molecules: Weakly bound complexes They are present as minor rather than trace species. One likely origin of continuum absorption. Observed on Earth (gas) and Jupiter (gas; (H)), Ganymede, Europa and Callisto (condensed), and in the laboratory (gas/condensed). Never on Venus/Mars, where there must be CO X NOT contained in the common spectral libraries

19 Earth s Transmission Spectrum Near-IR HK 4 CH HO 1.5 CO μm.0.5

20 Kaltenegger & Traub Palle et al, 009

21 How deep we see in the planet atmosphere? h T(h, λ) h min? Are antropogenic signatures visible in the lower layers? Is there a surface signal? Traub, 009

22 Evolution of the Earth s Transmission Spectrum during the eclipse

23 How deep we see in the planet atmosphere? Evidences? Ref.: Kaltenegger & Traub 009

24 Reflection vs Transmission

25 Earth s Reflectance Spectrum: Earthshine Same instrumentation only two months apart μm

26 Reflected spectrum Transmission Spectrum Blue planet? O O 4 O O 4 CO CH CO CH O O O N μm Palle et al, 009.5

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28 Thus, the transmission spectrum of telluric planets contains more information for the atmospheric characterization than the reflected spectrum. And it is also less technically challenging But, how far are we from making the measurements?

29 CoRoT & KEPLER can provide this input Many other surveys: Plato, TESS, Ground-based searches,... Terrestrial inner-orbit planets based on their transits: - About 50 planets if most have R ~ 1.0 Re - About 185 planets if most have R ~ 1.3 Re - About 640 planets if most have R ~. Re (Or possibly some combination of the above) About 1% of the cases with two or more planets per system

30 F* - F* ( ) + F*( ) T Ap*a Aa A* A* F* + Noise + Noise

31 Differential transit spectroscopy M star + Earth : 1 () measurement Ss+p / Sp Wavelength (μm)

32 M8 star + 1 Earth... with the E-ELT ~5 h ~ 5 ~ 50 ~ 150 h Wavelength (μm) Wavelength (μm) Work in progress... h h

33 Still, we must pursue the characterization with direct observations Exploration of surface features Presence of continents Rotational period Localized surface biomarkers (vegetation) Orbital light curve Ocean glints and polarization effects

34 Conclusions We have obtained the Earths transmission spectra μm First order detection and characterization of the main constituents of the Earth's atmosphere Detection of the Ionosphere : Ca II, ( Mg, Fe,??) Detection of O O and O N interactions Offers more information than the reflectance spectra Using the measured Earth transmission spectrum and several stellar spectra, we compute the probability of characterizing a transiting earth with E-ELT For a Earth in the habitability zone of an M-star, it is possible to detect HO, O, CH4,CO (= Life) within a few tens of hours of observations.

35 Thank you

36 Thank you

37

38 The Ring effect Rotational Raman Scattering (RRS) Early evidence: Sky-scattered Fraunhofer lines were less deep but broader than solar lines Incident exiting λex-δλ, λex, λex+δλ frequency redistribution λex Incident λ + Stokes + incident photon Anti-Stokes branches difference/ ratio

39 The Ring effect: Rotational Raman scattering Vountas et al. (1998) Transmission spectrum Solar spectrum