Multi-Band Polarimetry of the Lunar Surface. I. Global Properties

Jeong, Minsup; Kim, Sungsoo S.; Garrick‐Bethell, I.; Park, So-Myoung; Sim, Chae Kyung; Jin, Ho; Min, Kyoung Wook; Choi, Young‐Jun

doi:10.1088/0067-0049/221/1/16

Cited by 30 publications

(20 citation statements)

References 26 publications

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“…Using the representative trend, we characterize the evolution of a crater's spectral trend as follows: (1) L decreases, reflecting reduced heterogeneity of surface material; (2) θ increases in highlands craters because the darkening process is dominant and reddening is limited due to the lack of iron content that is necessary for reddening; and (3) s changes from negative to zero and then positive, meaning that the timescale of darkening and reddening processes is shorter for brighter and less red materials, and vice versa. We also find that craters at low latitudes tend to evolve faster than those at high latitudes, consistent with previous studies on the latitudinal behavior of space weathering on the Moon (Hemingway et al, ; Jeong et al, ; Sim et al, ). Because of the minute variation of θ in mare craters, spectral trends appear parallel to each other, accounting for the offset trends of mare craters that have been previously reported (Wilcox et al ).…”

Section: Discussionsupporting

confidence: 92%

Spectral Trends of the Surface Regolith in Lunar Craters

Sim

Kim

2018

JGR Planets

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Using topography-corrected reflectance maps of the Moon, we present a new methodology for quantifying the spectral distribution of craters in the 750 nm reflectance and 950 nm/750 nm reflectance ratio space (R-C space) and investigate how the spectral trend changes as the crater matures and degrades. Considering more than 3,495 craters across the Moon, we calculate three parameters to describe spectral trends of the pixels in each crater: 95th-percentile length, clockwise rotation angle from the horizontal line, and statistical skewness along the principal axis of the distribution, as well as median values of the reflectance and the reflectance ratio. We find that the shape of the spectral trend of a crater in R-C space becomes shorter, steeper, and more skewed toward the upper left as it optically matures and topographically degrades. Skewness shows a similar relationship to topographical degradation in both mare and highland craters. The skewness is useful in age estimation because it can be calculated easily from reflectance data and is applicable to craters of large size or in low-iron-content regions where a topographic model is currently not available. Using these three parameters, one can define the representative trends of a group of craters. We show representative trends of craters with various iron contents at different latitudes. The trends are parallel to one another, with offset controlled by latitude and radial rotation controlled by local iron content; these observations integrate the results of previous studies that reported the two behaviors individually.Plain Language Summary On an airless body such as the Moon, it is known that the surface becomes darker and redder as it gets older. The degree of this alteration, however, varies from place to place because of the different influences of local environments, such as local composition, insolation angle, and impact flux of micrometeoroids. To investigate the process of maturation of the lunar surface, we make use of the reflectance and color of lunar craters, which are studied using shadow-removed images. In the 750 nm reflectance and 950 nm/750 nm reflectance ratio space (R-C space), a crater shows an elongated pixel distribution. For 3,495 craters across the Moon, we investigated the length, rotation angle, and skewness of the distribution, as well as the reflectance and color of each crater. We find that as a crater becomes darker, redder and topographically collapsed, its distribution becomes shorter, steeper, and more skewed toward the upper left, which corresponds to the darker and redder direction of the R-C space. Interestingly, the relationship between the skewness increase and topographical collapse is consistent across the mare and highland craters despite the differences in composition. Knowing the skewness of a crater is useful in maturity or age estimation in addition to the currently used methods such as measuring optical maturity, counting the number of craters per unit area, and modeling the state of the topographic diffusion. Anot...

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Section: Discussionsupporting

confidence: 92%

Spectral Trends of the Surface Regolith in Lunar Craters

Sim

Kim

2018

JGR Planets

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“…One of the major implications of the magnetosphere's influence on E‐W crater wall properties is that it creates an environment that may be used to separate the effects of the solar wind and micrometeoroid bombardment. Jeong et al () suggested that the micrometeoroid flux varies with latitude, so the EF‐PF effect and other latitude‐dependent spectral changes previously reported (Hemingway et al, ; Lemelin et al, ) could be partly affected by micrometeoroid processes, if micrometeoroid orbits are dominantly in the ecliptic plane. However, since the gravity of the Earth and its magnetosphere would have a negligible effect on the micrometeoroid flux at the Moon (Grün et al, ; Juhász & Horányi, ; also, see Text S2), the E‐W effect must be entirely due to solar wind flux differences.…”

Section: Resultsmentioning

confidence: 96%

Asymmetric Space Weathering on Lunar Crater Walls

Sim

Kim

Lucey

et al. 2017

Geophysical Research Letters

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Using new topography‐corrected spectral data from the SELENE spacecraft, here we report a new lunar crater property produced by space weathering. We find that the optical properties of north, south, east, and west walls vary systematically across the Moon; pole‐facing walls are brighter and less red (i.e., less mature) than their equator‐facing counterparts as latitude increases, which we explain by reduced solar wind flux in pole‐facing slopes. On the nearside, we find that east‐west differences in crater wall brightness and redness vary with longitude, which we explain by solar wind shielding as the Moon passes through the Earth's magnetosphere. Because micrometeoroids are largely unaffected by magnetosphere passage, the longitudinal effect is used to discriminate between micrometeoroid and solar wind effects. Thus, for the first time we quantify how surface optical properties vary with solar wind flux.

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“…To make it clear how large α max is, we compared the polarimetric phase curves with those of other solar system airless bodies ( Figure 5). Among them, the Moon and Mercury are observed well around their maximum polarization (see also, Jeong et al 2015;Dollfus & Auriere 1974). Both the Moon and Mercury have α max ∼ 100 • , which is significantly smaller than Icarus (see Figure 5 There are several possibilities resulting in the large α max .…”

Section: Comparison With Other Airless Bodies In the Solar Systemmentioning

confidence: 96%

Polarimetric Study of Near-Earth Asteroid (1566) Icarus

Ishiguro

Kuroda

Watanabe

et al. 2017

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We conducted a polarimetric observation of the fast-rotating near-Earth asteroid (1566) Icarus at large phase (Sun-asteroid-observer's) angles α= 57 • -141 • around the 2015 summer solstice. We found that the maximum values of the linear polarization degree are P max =7.32±0.25 % at phase angles of α max =124 • ±8 • in the V -band and P max =7.04±0.21 % at α max =124 • ±6 • in the R C -band. Applying the polarimetric slope-albedo empirical law, we derived a geometric albedo of p V =0.25±0.02, which is in agreement with that of Q-type taxonomic asteroids. α max is unambiguously larger than that of Mercury, the Moon, and another near-Earth S-type asteroid (4179) Toutatis but consistent with laboratory samples with hundreds of microns in size. The combination of the maximum polarization degree and the geometric albedo is in accordance with terrestrial rocks with a diameter of several hundreds of micrometers. The photometric function indicates a large macroscopic roughness. We hypothesize that the unique environment (i.e., the small perihelion distance q=0.187 au and a short rotational period of T rot =2.27 hours) may be attributed to the paucity of small grains on the surface, as indicated on (3200) Phaethon.

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Multi-Band Polarimetry of the Lunar Surface. I. Global Properties

Cited by 30 publications

References 26 publications

Spectral Trends of the Surface Regolith in Lunar Craters

Spectral Trends of the Surface Regolith in Lunar Craters

Asymmetric Space Weathering on Lunar Crater Walls

Polarimetric Study of Near-Earth Asteroid (1566) Icarus

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