J/A+A/523/A57 The Earth as a transiting planet (Vidal-Madjar+, 2010)
The Earth as an extrasolar transiting planet:
Earth's atmosphere composition and thickness revealed by Lunar eclipse
observations.
Vidal-Madjar A., Arnold L., Ehrenreich D., Ferlet R.,
Lecavelier des Etangs A., Bouchy F., Segransan D., Boisse I., Hebrard G.,
Moutou C., Desert J.-M., Sing D.K., Cabanac R., Nitschelm C., Bonfils X.,
Delfosse X., Desort M., Diaz R.F., Eggenberger A., Forveille T.,
Lagrange A.-M., Lovis C., Pepe F., Perrier C., Pont F., Santos N.C., Udry S.
<Astron. Astrophys. 523, A57 (2010)>
=2010A&A...523A..57V 2010A&A...523A..57V
ADC_Keywords: Earth ; Spectroscopy
Keywords: eclipses - Earth - planets and satellites: atmospheres -
astrobiology - techniques: spectroscopic - methods: observational
Abstract:
An important goal within the quest for detecting an Earth-like
extrasolar planet, will be to identify atmospheric gaseous
bio-signatures. Aims. Observations of the light transmitted through
the Earth's atmosphere, as for an extrasolar planet, will be the first
important step for future comparisons. We have completed observations
of the Earth during a lunar eclipse, a unique situation similar to
that of a transiting planet. We aim at showing what species could be
detected in its atmosphere at optical wavelengths, where a lot of
photons are available in the masked stellar light.
We present observations of the 2008 August 16 Moon eclipse performed
with the SOPHIE spectrograph at the Observatoire de Haute- Provence
(France). Locating the spectrograph's fibers in the penumbra of the
eclipse, the Moon irradiance is then a mix of direct, unabsorbed Sun
light and solar light that has passed through the Earth's atmosphere.
This mixture essentially reproduces what is recorded during the
transit of an extrasolar planet.
We report here the clear detection of several Earth atmospheric
compounds in the transmission spectra, such as ozone, molecular
oxygen, and neutral sodium as well as molecular nitrogen and oxygen
through the Rayleigh signature. Moreover, we present a method that
allows us to derive the thickness of the atmosphere versus the
wavelength for penumbra eclipse observations. We quantitatively
evaluate the altitude at which the atmosphere becomes transparent for
important species like molecular oxygen and ozone, two species thought
to be tightly linked to the presence of life.
The molecular detections presented here are an encouraging first
attempt, necessary to better prepare for the future of extremely-large
telescopes and transiting Earth-like planets. Instruments like SOPHIE
will be mandatory when characterizing the atmospheres of transiting
Earth-like planets from the ground and searching for bio-marker
signatures.
Description:
Spectral distribution of the effective height h of the Earth
atmosphere as observed with the SOPHIE instrument on the 193cm
telescope at the Observatoire de Haute-Provence during the 16 August
2008 Lunar eclipse. These evaluations are made at about 2Å and
0.02Å spectral resolution.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig9o3.dat 34 1471 Ozone, 2Å resolution
fig10na.dat 34 1200 NaI, 0.02Å resolution
fig11o2b.dat 34 8000 O2 B(0-1), 6880Å, 0.02Å resolution
fig12o2g.dat 34 6000 O2 γ(2-0), 6280Å, 0.02Å resolution
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Byte-by-byte Description of file: fig*
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Bytes Format Units Label Explanations
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7- 15 F9.4 0.1nm lambda Wavelength
24- 34 E11.5 km h Effective altitude (1)
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Note (1): h,is the effective altitude extracted from the observations as
plotted in the corresponding figures in thick solid line. The E11.5
format is in double precision as e.g. 2.5853e+001.
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Acknowledgements:
Alfred Vidal-Madjar, alf(at)iap.fr
(End) Patricia Vannier [CDS] 06-Jul-2010