Polarimetric remote sensing of Solar System objects

Mishchenko, Michael I.; Rosenbush, V. K.; Kiselev, N. N.; Lupishko, D. F.; Tishkovcts, V. P.; Kaydash, V. G.; Belskaya, I. N.; Efimov, Y. S.; Shakhovskoy, N. M.

doi:10.15407/akademperiodyka.134.291

Cited by 82 publications

(60 citation statements)

References 229 publications

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“…The curves for the total flux scattered by both types of liquid water droplets have a strong forward scattering peak at the largest values of α (the smallest single scattering angles), which is due to refraction and depends mostly on the size of the scattering particles, and not so much on their shape (Mishchenko et al 2010). Another characteristic of the flux phase function of the droplets is the primary rainbow, that is due to light that has been reflected once inside the particles.…”

Section: The Cloud Particlesmentioning

confidence: 99%

Looking for the rainbow on exoplanets covered by liquid and icy water clouds

Karalidi

Stam

Hovenier

2012

A&A

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Aims. Looking for the primary rainbow in starlight that is reflected by exoplanets appears to be a promising method to search for liquid water clouds in exoplanetary atmospheres. Ice water clouds, that consist of water crystals instead of water droplets, could potentially mask the rainbow feature in the planetary signal by covering liquid water clouds. Here, we investigate the strength of the rainbow feature for exoplanets that have liquid and icy water clouds in their atmosphere, and calculate the rainbow feature for a realistic cloud coverage of Earth. Methods. We calculate flux and polarization signals of starlight that is reflected by horizontally and vertically inhomogeneous Earth-like exoplanets, covered by patchy clouds consisting of liquid water droplets or water ice crystals. The planetary surfaces are black. Results. On a planet with a significant coverage of liquid water clouds only, the total flux signal shows a weak rainbow feature. Any coverage of the liquid water clouds by ice clouds, however, dampens the rainbow feature in the total flux, and thus the discovery of liquid water in the atmosphere. On the other hand, detecting the primary rainbow in the polarization signal of exoplanets appears to be a powerful tool for detecting liquid water in exoplanetary atmospheres, even when these clouds are partially covered by ice clouds. In particular, liquid water clouds covering as little as 10-20% of the planetary surface, with more than half of these covered by ice clouds, still create a polarized rainbow feature in the planetary signal. Indeed, calculations of flux and polarization signals of an exoplanet with a realistic Earth-like cloud coverage, show a strong polarized rainbow feature.

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Section: The Cloud Particlesmentioning

confidence: 99%

Looking for the rainbow on exoplanets covered by liquid and icy water clouds

Karalidi

Stam

Hovenier

2012

A&A

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“…The reason is that the state of polarisation of starlight that is reflected by a planet is very sensitive to the composition and structure of the planetary atmosphere and surface (if present) (see Hansen & Travis 1974;Hovenier et al 2004;Mishchenko et al 2010, and references therein). An early example of this application of polarimetry is the derivation of the composition and size distribution of the droplets forming the upper Venusian clouds as well as the cloud top altitudes from Earth-based, disk-integrated Venus observations by Hansen & Hovenier (1974).…”

Section: Introductionmentioning

confidence: 99%

Flux and polarisation spectra of water clouds on exoplanets

Karalidi

Stam

Hovenier

2011

A&A

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Context.A crucial factor for a planet's habitability is its climate. Clouds play an important role in planetary climates. Detecting and characterising clouds on an exoplanet is therefore crucial when addressing this planet's habitability. Aims. We present calculated flux and polarisation spectra of starlight that is reflected by planets covered by liquid water clouds with different optical thicknesses, altitudes, and particle sizes, as functions of the phase angle α. We discuss the retrieval of these cloud properties from observed flux and polarisation spectra. Methods. Our model planets have black surfaces and atmospheres with Earth-like temperature and pressure profiles. We calculate the spectra from 0.3 to 1.0 μm, using an adding-doubling radiative transfer code with integration over the planetary disk. The cloud particles' scattering properties are calculated using a Mie-algorithm. Results. Both flux and polarisation spectra are sensitive to the cloud optical thickness, altitude and particle sizes, depending on the wavelength and phase angle α. Conclusions. Reflected fluxes are sensitive to cloud optical thicknesses up to ∼40, and the polarisation to thicknesses up to ∼20. The shapes of polarisation features as functions of α are relatively independent of the cloud optical thickness. Instead, they depend strongly on the cloud particles' size and shape, and can thus be used for particle characterisation. In particular, a rainbow strongly indicates the presence of liquid water droplets. Single scattering features such as rainbows, which can be observed in polarisation, are virtually unobservable in reflected fluxes, and fluxes are thus less useful for cloud particle characterisation. Fluxes are sensitive to cloud top altitudes mostly for α < 60 • and wavelengths <0.4 μm, and the polarisation for α around 90 • and wavelengths between 0.4 and 0.6 μm.

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“…It produces a narrow branch of negative polarisation usually accompanied by a narrow brightness opposition effect. Such narrow surges both in polarisation and brightness, typically centred at α ∼ 0.4-1 • , have been found for high-albedo planetary satellites and asteroids (see Mishchenko et al 2010, for a review). The relationship of polarisation degree and albedo may help to distinguish between different mechanisms of the negative polarisation.…”

Section: What Is the Most Probable Cause Of The Negative Polarisationmentioning

confidence: 66%

Polarimetry of trans-Neptunian objects (136472) Makemake and (90482) Orcus

Belskaya

Bagnulo

Stinson

et al. 2012

A&A

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Context. We study the surface properties of trans-Neptunian populations of solar system bodies. Aims. We investigate the surface characteristics of the dwarf planet (136472) Makemake and the resonant object (90482) Orcus. Methods. Using the FORS2 instrument of the ESO-VLT, we carried out linear polarisation measurements of Makemake and Orcus. Results. Polarisation of Orcus is similar to that of smaller-sized objects. The polarimetric properties of Makemake are very close to those of Eris and Pluto. We did not find any significant differences in the polarisation properties of trans-Neptunian objects (TNOs) from different dynamical classes. However, there are significant differences in the polarisation of the large objects and the smaller ones and between large TNOs with water-ice and methane-ice dominated surfaces. Conclusions. We confirm the different types of polarisation phase behaviour for the largest and smaller-sized TNOs. To explain subtle surface polarisation of Pluto, Makemake and Eris, we assume that their surfaces are covered by a thin layer of hoarfrost masking the surface structure.

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Polarimetric remote sensing of Solar System objects

Cited by 82 publications

References 229 publications

Looking for the rainbow on exoplanets covered by liquid and icy water clouds

Looking for the rainbow on exoplanets covered by liquid and icy water clouds

Flux and polarisation spectra of water clouds on exoplanets

Polarimetry of trans-Neptunian objects (136472) Makemake and (90482) Orcus

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