A test for the search for life on extrasolar planets

Arnold, L.; Gillet, S.; Lardière, Olivier; Riaud, Pierre; Schneider, Jodi

doi:10.1051/0004-6361:20020933

Cited by 152 publications

(92 citation statements)

References 18 publications

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“…The diurnal photometric variability could be measured. Ford, Seager, & Turner (2001) have shown that for an earthlike planet, variation on the order of 100% may be expected.…”

Section: Discussionmentioning

confidence: 99%

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The Spectrum of Earthshine: A Pale Blue Dot Observed from the Ground

Woolf

Smith

Traub

et al. 2002

ApJ

218

183

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We report the visible reflection spectrum of the integrated Earth, illuminated as it would be seen as a spatially unresolved extrasolar planet. The spectrum was derived from observation of lunar earthshine in the range 4800-9200 Å at a spectral resolution of about 600. We observe absorption features of ozone, molecular oxygen, and water. We see enhanced reflectivity at short wavelengths from Rayleigh scattering and apparently negligible contributions from aerosol and ocean water scattering. We also see enhanced reflectivity at long wavelengths starting at about 7300 Å , corresponding to the well-known red reflectivity edge of vegetation because of its chlorophyll content; however, this signal is not conclusive because of the breakdown of our simple model at wavelengths beyond 7900 Å .

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“…The diurnal photometric variability could be measured. Ford, Seager, & Turner (2001) have shown that for an earthlike planet, variation on the order of 100% may be expected.…”

Section: Discussionmentioning

confidence: 99%

“…We suggest that further observations of earthshine should be made; one group has already done so (Arnold et al 2002). One purpose is to validate our ability to characterize extrasolar terrestrial planets using visible wavelengths.…”

Section: Commentsmentioning

confidence: 99%

The Spectrum of Earthshine: A Pale Blue Dot Observed from the Ground

Woolf

Smith

Traub

et al. 2002

ApJ

218

183

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“…at lower altitudes, like the presence of clouds, continents, oceans etc. as shown in Arnold et al (2002), Woolf et al (2002), Arnold (2008, and references therein). Indeed, in the core of the spectral lines we will sample only the upper atmosphere, where one can expect that the mixing of different species has already taken place, thus revealing an "average" planetary atmosphere representative of overall signatures.…”

Section: Introductionmentioning

confidence: 92%

The Earth as an extrasolar transiting planet

Vidal‐Madjar

Arnold

Ehrenreich

et al. 2010

A&A

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Context. 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. Methods. 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. Results. 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. Conclusions. 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.

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“…To anticipate the analysis of terrestrial exoplanet images, in particular the detection of life, we investigate the Earthshine that can be linked with the global Earth's albedo, as showed by Arnold et al (2002) and Woolf et al (2002). If life exists on an extrasolar planet, it may present unusual and unknown forms.…”

Section: Introductionmentioning

confidence: 99%

“…This idea was completely forgotten until about 1998, when Jean Schneider proposed to do such observations again. Following a first attempt made at the Observatoire de Haute Provence (Arnold et al 2002), which successfully showed the feasibility of such a measurement, we used the New Technology Telescope of ESO to measure the VRE. We obtained a lower signal (VRE = 1.3 %) when the Pacific Ocean faces the Moon than when Africa faces the Moon (VRE = 3-4 %) (Hamdani et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Present and Future Detection of Terrestrial Biomarkers on Earthshine

Briot¹,

Arnold²,

Jacquemoud³

2012

Proc. IAU

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Abstract. In the context of life detection on terrestrial exoplanets, new methods of search for spectral signatures of chlorophyll and other biomarkers in the Earthshine have been developed in the last few decades. Astronomical observations made at OHP and ESO (NTT) showed a significant signal when continents are facing the Moon. This signal, called the Vegetation Red Edge (VRE), is undoubtedly due to chlorophyll absorption properties. In order to strengthen these results, the LUCAS (LUmière Cendrée en Antarctique par Spectroscopie) project dedicated to the measurement of the Earthshine from the Concordia Research Station (C Dome, Antarctica) has been set up. One of the objectives of LUCAS was to observe prolonged variations of the VRE corresponding to various parts of the Earth facing the Moon. An extension of this project, called LUCAS II, would allow long-term observations to detect seasonal variations of the vegetation signal. These data, together with accurate measurements of the Earth's albedo, will help validate a model of global and spectral albedo of our planet.

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A test for the search for life on extrasolar planets

Cited by 152 publications

References 18 publications

The Spectrum of Earthshine: A Pale Blue Dot Observed from the Ground

The Spectrum of Earthshine: A Pale Blue Dot Observed from the Ground

The Earth as an extrasolar transiting planet

Present and Future Detection of Terrestrial Biomarkers on Earthshine

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