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Ceres observed at low phase angles by VIR-Dawn

Ciarniello, M. and De Sanctis, M. C. and Raponi, A and Rousseau, B. and Longobardo, A. and Li, J.-Y and Schröder, Stefan and Tosi, F. and Zambon, F. and Ammannito, E. and Carrozzo, F.G. and Frigeri, A. and Rognini, E. and Raymond, C. A. and Russell, C. T. (2020) Ceres observed at low phase angles by VIR-Dawn. Astronomy & Astrophysics, 634, A39. EDP Sciences. doi: 10.1051/0004-6361/201936492. ISSN 0004-6361.

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Official URL: https://www.aanda.org/articles/aa/abs/2020/02/aa36492-19/aa36492-19.html


Context. Particulate surfaces exhibit a surge of reflectance at low phase angles, a phenomenon referred to as the opposition effect (OE). Two mechanisms are recognized as responsible for the OE: shadow hiding (SH) and coherent backscattering. The latter is typically characterized by a small angular width of a few degrees at most and according to the theoretical prediction should exhibit wavelength and albedo dependence. Aims. We characterize the OE on the surface of Ceres using Dawn Visible InfraRed mapping spectrometer hyperspectral images at low phase angles. Furthermore, this dataset, coupled with previous observations, allows us to perform a complete spectrophotometric modeling at visual-to-infrared (VIS-IR) wavelengths (0.465-4.05 µm) in the broad phase angle range ≈ 0°-132°. Methods. We applied Hapke's theory to the average phase curve for Ceres. Disk-resolved properties of the OE were investigated through an empirical model. Results. Across the investigated phase angle interval, Ceres' average phase curve exhibits a smaller back-scattering contribution for increasing wavelengths. This determines a progressive spectral reddening at larger phase angles that we hypothesize as being related to the effect of submicron roughness on the grain surface. In the OE region, the shape of the phase curves is fairly constant across the VIS range and no sharp opposition surge at very small phase angles (α < 2°) can be recognized. This would suggest a major contribution from SH to Ceres' OE. Assuming SH as the dominant mechanism, from the OE angular width we infer a high surface porosity (≈0.9), which appears in good qualitative agreement with Ceres' low thermal inertia. Thanks to the OE observations we derive Ceres’ VIS-IR geometric albedo with a reference value at 0.55 µm of 0.098±0.007. Mapping of the VIS normal albedo and OE angular width across a portion of the surface of Ceres does not reveal a spatial correlation between these quantities, consistent with SH dominating in the α = 0°-7° interval. The comparison of Ceres' V-band magnitude curve with that of other asteroids indicates that Ceres' OE is typical of a low-albedo object and compatible with the C-class type.

Item URL in elib:https://elib.dlr.de/134651/
Document Type:Article
Title:Ceres observed at low phase angles by VIR-Dawn
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Ciarniello, M.INAF–IAPS, Istituto di Astrofisica e Planetologia Spaziali, Area di Ricerca di Tor Vergata, via del Fosso del Cavaliere, 100, 00133 Rome, ItalyUNSPECIFIEDUNSPECIFIED
Raponi, AINAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Rome, ItalyUNSPECIFIEDUNSPECIFIED
Longobardo, A.INAF-IAPS, Via del Fosso del Cavaliere 100, I-00133 Rome, ItalyUNSPECIFIEDUNSPECIFIED
Li, J.-YPlanetary Science Institute, Tucson, Arizona 85719, USAUNSPECIFIEDUNSPECIFIED
Schröder, StefanUNSPECIFIEDhttps://orcid.org/0000-0003-0323-8324UNSPECIFIED
Tosi, F.INAF-IAPS, Via del Fosso del Cavaliere 100, I-00133 Rome, ItalyUNSPECIFIEDUNSPECIFIED
Zambon, F.INAF-IAPS, Via del Fosso del Cavaliere 100, I-00133 Rome, ItalyUNSPECIFIEDUNSPECIFIED
Carrozzo, F.G.INAF-IAPS, Via del Fosso del Cavaliere 100, I-00133 Rome, ItalyUNSPECIFIEDUNSPECIFIED
Frigeri, A.INAF-IAPS, Via del Fosso del Cavaliere 100, I-00133 Rome, ItalyUNSPECIFIEDUNSPECIFIED
Raymond, C. A.Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, USAUNSPECIFIEDUNSPECIFIED
Russell, C. T.UCLA, Los Angeles, California, USAUNSPECIFIEDUNSPECIFIED
Journal or Publication Title:Astronomy & Astrophysics
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:Yes
Page Range:A39
Publisher:EDP Sciences
Keywords:minor planets, asteroids: individual: Ceres, methods: data analysis, techniques: photometric, radiative transfer, techniques: imaging spectroscopy, planets and satellites: surfaces
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Space Exploration
DLR - Research theme (Project):R - Project DAWN (old)
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Geology
Deposited By: Schröder, Dr. Stefan
Deposited On:22 Apr 2020 07:02
Last Modified:22 Apr 2020 07:02

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