Characterization of a photometric anomaly in lunar Mare Nubium

• Viktor Korokhin^a,

• Yuriy Shkuratov^a,

• Vadym Kaydash^a,

• Alexander Basilevsky^b,

• Larysa Rohachova^a,

• Yuri Velikodsky^{a, c},

• Nickolay Opanasenko^a,

• Gorden Videen^{d, e},

• Dmitry Stankevich^a,

• Olena Kaluhina^a

• ^a Institute of Astronomy, Kharkiv V.N. Karazin National University, 35 Sumskaya St., Kharkiv 61022, Ukraine

• ^b Institute of Geochemistry and Analytical Chemistry, RAS, 19 Kosygin St., Moscow 117975, Russia

• ^c National Aviation University, Cosmonaut Komarov Ave. 1, Kiev 03680, Ukraine

• ^d Army Research Laboratory AMSRL-CI-EM, 2800 Powder Mill Road, Adelphi, MD 20783, USA

• ^e Space Science Institute, 4750 Walnut St. Suite 205, Boulder, CO 80301, USA

Received 22 July 2015, Revised 26 October 2015, Accepted 14 January 2016, Available online 26 January 2016

Highlights

• A novel method allows to construct seamless reflectance mosaics using LROC WAC data.

• New mosaics have been applied to analyze the photometric anomaly in Mare Nubium.

• The anomaly can be explained by the difference of surface structure from vicinity.

• This area may be a shallow flooding of an elevated formation of highland composition.

• The material of which could have been excavated and mixed up with upper layers.

Abstract

A novel approach of constructing photometrically seamless mosaics of reflectance, color-ratios, and phase–curve slopes using LROC WAC images has been developed, which can be used to map the photometric parameters of the lunar surface. The approach takes into account both geometric corrections with data on local topography and photometric conjunctions using our simple photometric model. New mosaics obtained with the technique allow more reliable studies of structural and chemical characteristics of the lunar surface. This approach has been applied to analyze the photometric anomaly (21.6 S, 17.7 W, ~40 km in size) in Mare Nubium detected earlier with our Earth-based observations. For each point of the scene the parameters were calculated using the least-square method for several tens of source WAC images. Clementine mosaics also were used in the analysis, e.g., in order to estimate the parameter of maturity degree I_s/FeO. The anomaly has low FeO and TiO₂ abundance and reveals a higher slope of the phase function than surroundings. Thermal data from LRO Diviner measurements do not show anomalies in this region. We consider this area as a shallow flooding of an elevated formation of highland composition, the material of which could have been excavated and mixed up with upper layers of the lunar surface through meteoroid impacts. The anomalous behavior of the phase function can be explained by the difference of surface structure in the anomaly and surrounding regions on the scale of less than several centimeters. This may be due to larger quantities of small fragments of rocks and clumps on the surface and/or the presence of agglomerates having open structure.

Keywords

• Moon;

• Surface;

• Mare Nubium;

• Photometry;

• Colorimetry;

• Mosaics;

• Phase function;

• Surface anomaly;

• Chemical composition;

• Lunar Reconnaissance Orbiter (LRO);

• Wide angle camera (WAC);

• Clementine UVVIS data

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