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Lunar swirls are albedo features associated with magnetic anomalies, and their formation mechanism has long been debated. Because spectral properties of lunar swirls provide information on space weathering environments and surface compositions, differences in the spectra between swirls and background regions can give a clue to their formation. We analyze space weathering for swirls in the lunar highlands and maria using the VIS-NIR spectral slope, 1550 nm reflectance, and 950 nm band depth. We find that highland swirls show lower reddening-to-darkening ratios than off-swirl regions, implying more decreases of nanophase iron relative to microphase iron on swirls. We also use magnetic field data to investigate the influence of the crustal magnetic field on the space weathering of a few selected swirls. The Reiner Gamma swirl becomes more immature as the magnetic field strength increases, although the entire swirl has a high albedo. Especially, the Reiner Gamma tail shows that the stronger magnetic field makes the surface undergo less spectral reddening. Our results support the solar wind stand-off hypothesis, which is that the solar wind deflected by the crustal field determines the optical property of the surface. [ABSTRACT FROM AUTHOR]

Our previous study shows that the angle of linear polarization (AOLP) of solar radiation that is scattered from clouds at near-backscatter angles can be used to detect super-thin cirrus clouds over oceans. Such clouds are too thin to be sensed using any current passive satellite instruments that only measure light's total intensity, because of the uncertainty in surface reflection. In this report, we show that with a method similar to the super-thin cloud detection algorithm, dust aerosols may also be detected and differentiated from clouds. We also show that the degree of polarization of reflected light can be used for retrieving the optical depth of dust aerosols in the neighborhood of the backscatter angle, regardless of the reflecting surface conditions. This is a simple and robust algorithm, which could be used to survey dust aerosols over midlatitude and tropical oceans. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: We derived the mole fraction of H2 in the troposphere of Titan from an analysis of the H2–N2 dimer S0(0) rotational transition seen near 355cm−1 in spectra recorded by the Composite Infra-Red Spectrometer (CIRS) on the Cassini spacecraft between March 2006 and February 2007. We find a globally-averaged value of (9.6±2.4)×10−4, consistent with the earlier determination based on the Voyager IRIS dataset, and with the value obtained from the Gas Chromatograph Mass Spectrometer (GCMS) experiment on the Huygens probe, but a factor of ∼4 lower than that measured by the Ion and Neutral Mass Spectrometer (INMS) in the 1025–1475km altitude range. Interestingly, the latitudinal distribution of H2 appears to be non-uniform, with a mole fraction above 50°N in excess of 30–70% (±40%) relatively to the globally-averaged value. Such a non-uniform distribution is unexpected since H2 is thought to be chemically inert in the lower atmosphere of Titan. It is proposed that the observed enhancement in the north polar region is caused by downwelling occurring during the winter season in the polar vortex. This interpretation is dependent on the existence of a vertical gradient of the H2 concentration in the stratosphere, as suggested by the differences between the INMS values and those measured by GCMS and CIRS, although such a gradient is not consistent with the present understanding of dynamics and chemistry in Titan''s atmosphere. [Copyright &y& Elsevier]