Variations of the apparent angular size of the Sun across the entire Solar System: Implications for planetary opposition surges

Déau, E.

doi:10.1016/j.jqsrt.2012.02.040

Cited by 10 publications

(10 citation statements)

References 80 publications

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“…5C. The reflectance is well reproduced and reaches a plateau below 0.05 • phase, likely due to the finite size of the Sun (Shkuratov et al 1999;Déau 2012). To model this phenomenon, we follow Déau (2012) and adopt the empirical limb darkening model from Hestroffer & Magnan (1998):…”

Section: Akimov Modelmentioning

confidence: 99%

Ceres’ opposition effect observed by the Dawn framing camera

Schröder

Rayman

et al. 2018

A&A

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Context. The surface reflectance of planetary regoliths may increase dramatically towards zero phase angle, a phenomenon known as the opposition effect (OE). Two physical processes that are thought to be the dominant contributors to the brightness surge are shadow hiding (SH) and coherent backscatter (CB). The occurrence of shadow hiding in planetary regoliths is self-evident, but it has proved difficult to unambiguously demonstrate CB from remote sensing observations. One prediction of CB theory is the wavelength dependence of the OE angular width. Aims. The Dawn spacecraft observed the OE on the surface of dwarf planet Ceres. We aim to characterize the OE over the resolved surface, including the bright Cerealia Facula, and to find evidence for SH and/or CB. It is presently not clear if the latter can contribute substantially to the OE for surfaces as dark as that of Ceres. Methods. We analyze images of the Dawn framing camera by means of photometric modeling of the phase curve.Results. We find that the OE of most of the investigated surface has very similar characteristics, with an enhancement factor of 1.4 and a full width at half maximum of 3 • ("broad OE"). A notable exception are the fresh ejecta of the Azacca crater, which display a very narrow brightness enhancement that is restricted to phase angles < 0.5 • ("narrow OE"); suggestively, this is in the range in which CB is thought to dominate. We do not find a wavelength dependence for the width of the broad OE, and lack the data to investigate the dependence for the narrow OE. The prediction of a wavelength-dependent CB width is rather ambiguous, and we suggest that dedicated modeling of the Dawn observations with a physically based theory is necessary to better understand the Ceres OE. The zero-phase observations allow us to determine Ceres' visible geometric albedo as p V = 0.094 ± 0.005. A comparison with other asteroids suggests that Ceres' broad OE is typical for an asteroid of its spectral type, with characteristics that are primarily linked to surface albedo. Conclusions. Our analysis suggests that CB may occur on the dark surface of Ceres in a highly localized fashion. While the results are inconclusive, they provide a piece to the puzzle that is the OE of planetary surfaces.

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Section: Akimov Modelmentioning

confidence: 99%

Ceres’ opposition effect observed by the Dawn framing camera

Schröder

Rayman

et al. 2018

A&A

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“…Since the effect of non-zero angular size of the Sun is a concern for objects in the inner and outer solar system, we computed the angular radius of the Sun for 67P using the following expression (Déau 2012 and references therein):…”

Section: Local Phase Curvementioning

confidence: 99%

Opposition effect on comet 67P/Churyumov-Gerasimenko using Rosetta-OSIRIS images

Masoumzadeh

Oklay

Kolokolova

et al. 2017

A&A

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Aims. We aim to explore the behavior of the opposition effect as an important tool in optical remote sensing on the nucleus of comet 67P/ Churyumov-Gerasimenko (67P), using Rosetta-OSIRIS images acquired in different filters during the approach phase, July-August 2014 and the close flyby images on 14 of February 2015, which contain the spacecraft shadow. Methods. We based our investigation on the global and local brightness from the surface of 67P with respect to the phase angle, also known as phase curve. The local phase curve corresponds to a region that is located at the Imhotep-Ash boundary of 67P. Assuming that the region at the Imhotep-Ash boundary and the entire nucleus have similar albedo, we combined the global and local phase curves to study the opposition-surge morphology and constrain the structure and properties of 67P. The model parameters were furthermore compared with other bodies in the solar system and existing laboratory study. Results. We found that the morphological parameters of the opposition surge decrease monotonically with wavelength, whereas in the case of coherent backscattering this behavior should be the reverse. The results from comparative analysis place 67P in the same category as the two Mars satellites, Phobos and Deimos, which are notably different from all airless bodies in the solar system. The similarity between the surface phase function of 67P and a carbon soot sample at extremely small angles is identified, introducing regolith at the boundary of the Imhotep-Ash region of 67P as a very dark and fluffy layer.

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“…The consistency of the phase slopes and the opposition effect amplitudes between 10-km asteroids and sub-km asteroid JU3 may suggest that the magnitude-phase relation would be dominated by the albedo, not by the asteroid diameter. The amplitude and width of the opposition effect are considered to represent the distance from the sun theoretically (Déau 2012). The effect is caused by the apparent size of the sun when viewed from asteroids.…”

Section: Shevchenko Function Fittingmentioning

confidence: 99%

OPTICAL PROPERTIES OF (162173) 1999 JU3: IN PREPARATION FOR THE JAXAHAYABUSA 2SAMPLE RETURN MISSION

Ishiguro

Kuroda

Hasegawa

et al. 2014

ApJ

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We investigated the magnitude-phase relation of (162173) 1999 JU3, a target asteroid for the JAXA Hayabusa 2 sample return mission. We initially employed the international Astronomical Union's H-G formalism but found that it fits less well using a single set of parameters. To improve the inadequate fit, we employed two photometric functions, the Shevchenko and Hapke functions. With the Shevchenko function, we found that the magnitude-phase relation exhibits linear behavior in a wide phase angle range (α = 5-75 • ) and shows weak nonlinear opposition brightening at α < 5 • , providing a more reliable absolute magnitude of H V = 19.25 ± 0.03. The phase slope (0.039 ± 0.001 mag deg −1 ) and opposition effect amplitude (parameterized by the ratio of intensity at α=0.3 • to that at α=5 • , I(0.3 • )/I(5 • )=1.31±0.05) are consistent with those of typical Ctype asteroids. We also attempted to determine the parameters for the Hapke model, which are applicable for constructing the surface reflectance map with the Hayabusa 2 onboard cameras. Although we could not constrain the full set of Hapke parameters, we obtained possible values, w=0.041, g=-0.38, B 0 =1.43, and h=0.050, assuming a surface roughness parameterθ=20 • . By combining our photometric study with a thermal model of the asteroid (Müller et al. in preparation), we obtained a geometric albedo of p v = 0.047 ± 0.003, phase integral q = 0.32 ± 0.03, and Bond albedo A B = 0.014 ± 0.002, which are commensurate with the values for common C-type asteroids.

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Variations of the apparent angular size of the Sun across the entire Solar System: Implications for planetary opposition surges

Cited by 10 publications

References 80 publications

Ceres’ opposition effect observed by the Dawn framing camera

Ceres’ opposition effect observed by the Dawn framing camera

Opposition effect on comet 67P/Churyumov-Gerasimenko using Rosetta-OSIRIS images

OPTICAL PROPERTIES OF (162173) 1999 JU3: IN PREPARATION FOR THE JAXAHAYABUSA 2SAMPLE RETURN MISSION

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