Phase Variation of Earthshine Polarization Spectra

Takahashi, Jun; Itoh, Yoichi; Akitaya, Hiroshi; Okazaki, Akira; Kawabata, Koji S.; Oasa, Yumiko; Isogai, M.

doi:10.1093/pasj/65.2.38

Cited by 29 publications

(44 citation statements)

References 37 publications

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“…Various groups (Dollfus 1957;Wolstencroft & Breon 2005;Sterzik et al 2012;Takahashi et al 2013;Bazzon et al 2013) have reported a similar property. In our data, we observe that the linear polarization intensity remains nearly constant at about 5.7% between ∼0.8 μm and 0.9 μm.…”

Section: Resultsmentioning

confidence: 87%

“…This can be done by observing the earthshine, which is the sunlight scattered by the dayside Earth and reflected by the nightside of the Moon. The optical and near-infrared earthshine spectra reveal atmospheric and surface biosignatures and are sensitive to features like water clouds, oceans, deserts, and volcanic activity (e.g., Woolf et al 2002;Turnbull et al 2006;Montañés-Rodríguez et al 2006;Pallé et al 2009;García Muñoz et al 2012); many are present in the earthshine optical spectropolarimetric data (Sterzik et al 2012;Takahashi et al 2013).…”

Section: Introductionmentioning

confidence: 99%

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Simultaneous optical and near-infrared linear spectropolarimetry of the earthshine

Miles-Páez

Πάλλη

Osorio

2014

A&A

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Aims. We aim to extend our current observational understanding of the integrated planet Earth spectropolarimetry from the optical to the near-infrared wavelengths. Major biomarkers like O 2 and water vapor are strong flux absorbents in the Earth's atmosphere, and some linear polarization of the reflected stellar light is expected to occur at these wavelengths. Methods. Simultaneous optical (0.4−0.9 μm) and near-infrared (0.9−2.3 μm) linear spectropolarimetric data of the earthshine were acquired by observing the nightside of the waxing Moon. The data have sufficient spectral resolution (2.51 nm in the optical, and 1.83 and 2.91 nm in the near-infrared) to resolve major molecular species present in the Earth's atmosphere. Results. We find the highest values of linear polarization (≥10%) at the bluest wavelengths, which agrees with other studies. Linear polarization intensity steadily decreases toward red wavelengths reaching a nearly flat value beyond ∼0.8 μm. In the near-infrared, we measured a polarization degree of ∼4.5 % for the continuum. We report the detection of molecular features due to O 2 at 0.760, 1.25 μm, and H 2 O at 0.653-0.725 μm, 0.780-0.825 μm, 0.93, and 1.12 μm in the spectropolarimetric data, and most of them show high linear polarimetry degrees above the continuum. In particular, the broad H 2 O 1.12 μm band displays a polarimetric intensity as high as that of the blue optical. These features may become a powerful tool for characterizing Earth-like planets in polarized light.

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Section: Resultsmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Simultaneous optical and near-infrared linear spectropolarimetry of the earthshine

Miles-Páez

Πάλλη

Osorio

2014

A&A

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“…Another spectra-polarimetric observation of the earthshine was published by Takahashi et al (2013). They also find a rise in the fractional polarization of the earthshine toward the blue but with a much flatter slope.…”

Section: Comparison With Previous Measurementsmentioning

confidence: 90%

“…Therefore, only a qualitative comparison with our data can be made. The observations of Takahashi et al (2013) are conducted on five consecutive nights and cover phase angles α = 49…”

Section: Comparison With Previous Measurementsmentioning

confidence: 99%

Measurement of the earthshine polarization in theB, V, R, andIbands as function of phase

Bazzon

Schmid

Gisler

2013

A&A

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Context. Earth-like, extrasolar planets may soon become observable with upcoming high contrast polarimeters. Therefore, the characterization of the polarimetric properties of the planet Earth is important for interpreting expected observations and planning of future instruments. Aims. Benchmark values for the polarization signal of integrated light from the planet Earth in broad band filters are derived from new polarimetric observations of the earthshine backscattered from the Moon's dark side. Methods. The fractional polarization of the earthshine p es is measured in the B, V, R, and I filters for Earth-phase angles α between 30• and 110• with a new, specially designed wide field polarimeter. In the observations, the light from the bright lunar crescent is blocked with focal plane masks. Because the entire Moon is imaged, the earthshine observations can be corrected for the stray light from the bright lunar crescent and twilight. The phase dependence of p es is fitted by a function p es = q max sin 2 α. Depending on wavelength λ and the lunar surface albedo a, the polarization of the backscattered earthshine is significantly reduced. To determine the polarization of the planet Earth, we correct our earthshine measurements by a polarization efficiency function for the lunar surface (λ, a) derived from measurements of lunar samples from the literature. Results. The polarization of the earthshine decreases toward longer wavelengths and is about a factor 1.3 lower for the higher albedo highlands. For mare regions the measured maximum polarization is about q max,B = 13% for α = 90• (half moon) in the B band. The resulting fractional polarizations for the planet Earth derived from our earthshine measurements and corrected by (λ, a) are 24.6% for the B band, 19.1% for the V band, 13.5% for the R band, and 8.3% for the I band. Together with the literature values for the spectral reflectivity, we obtain a contrast C p between the polarized flux of the planet Earth and the (total) flux of the Sun with an uncertainty of less than 20%, and we find that the best phase for detecting an Earth twin is around α = 65• . Conclusions. The obtained results provide a multiwavelength and multiphase set of benchmark values that are useful for assessing different instrument and observing strategies for the future high contrast polarimetry of extrasolar planetary systems. Polarimetric models of Earth-like planets are in qualitative agreement with our results, but there are also significant differences that might guide more detailed computations.

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“…The size of the disk integrated rainbow polarisation signal for the Earth has not been measured, but in principle could be obtained from lunar earthshine polarisation measurements. Current data however does not have sufficient phase coverage (Sterzik, Bagnulo, & Palle 2012;Takahashi et al 2013;Bazzon, Schmidt, & Gisler 2013).…”

Section: Signatures Of Habitabilitymentioning

confidence: 99%

The Dawes Review 3: The Atmospheres of Extrasolar Planets and Brown Dwarfs

Bailey

2014

Publ. Astron. Soc. Aust.

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The last few years has seen a dramatic increase in the number of exoplanets known and in the range of methods for characterising their atmospheric properties. At the same time, new discoveries of increasingly cooler brown dwarfs have pushed down their temperature range which now extends down to Y-dwarfs of < 300 K. Modelling of these atmospheres has required the development of new techniques to deal with the molecular chemistry and clouds in these objects. The atmospheres of brown dwarfs are relatively well understood, but some problems remain, in particular the behavior of clouds at the L/T transition. Observational data for exoplanet atmosphere characterisation is largely limited to giant exoplanets that are hot because they are near to their star (hot Jupiters) or because they are young and still cooling. For these planets there is good evidence for the presence of CO and H2O absorptions in the IR. Sodium absorption is observed in a number of objects. Reflected light measurements show that some giant exoplanets are very dark, indicating a cloud free atmosphere. However, there is also good evidence for clouds and haze in some other planets. It is also well established that some highly irradiated planets have inflated radii, though the mechanism for this inflation is not yet clear. Some other issues in the composition and structure of giant exoplanet atmospheres such as the occurrence of inverted temperature structures, the presence or absence of CO2and CH4, and the occurrence of high C/O ratios are still the subject of investigation and debate.

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Phase Variation of Earthshine Polarization Spectra

Cited by 29 publications

References 37 publications

Simultaneous optical and near-infrared linear spectropolarimetry of the earthshine

Simultaneous optical and near-infrared linear spectropolarimetry of the earthshine

Measurement of the earthshine polarization in theB, V, R, andIbands as function of phase

The Dawes Review 3: The Atmospheres of Extrasolar Planets and Brown Dwarfs

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