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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]

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]

We have obtained 3.3–3.4-μm spectro-images of Jupiter including CH 4 and H 3 + emission lines from both polar regions at the Gemini North telescope. We find that the peak of the 3-μm CH 4 northern bright spot is located at ∼200° (SysIII) longitude, ∼20° west of the center of the 8-μm north-polar bright spot, and does not coincide with the 3-μm H 3 + bright spot. We derive high temperatures (500–850 K) from CH 4 rotational lines on the bright spots of both polar regions, above the 1-μbar pressure level, while we find cooler temperatures (<350 K) over the 8-μm spot. The intensity ratios of the various 3-μm vibrational bands of CH 4 are roughly constant, indicating that the upper states of these bands are mostly populated by non-thermal excitation mechanisms, such as auroral particle precipitation and/or Joule heating, in contrast with the 8-μm thermal emission. [ABSTRACT FROM AUTHOR]

Abstract: We present a Python-based data reduction pipeline package (PLP) for the Immersion GRating INfrared Spectrograph (IGRINS), an instrument that covers the complete H- and K-bands in one exposure with a spectral resolving power of 40,000. The reduction steps carried out by the PLP include flat-fielding, background removal, order extraction, distortion correction, wavelength calibration, and telluric correction using spectra of A type standard stars. As the spectrograph has no moving parts, the PLP automatically reduces the data using predefined functions for the processes of order extraction, distortion correction, and wavelength calibration. Before the telluric correction of the target spectra, the intrinsic hydrogen absorption features of the standard A star are removed with a Gaussian fitting algorithm. The final result is the flux of the target as a function of wavelength. Users can customize the predefined functions for the extraction of the spectrum from the echellogram and adjust the parameters for the fitting functions for the spectra of celestial objects, using “fine-tuning” options, as necessary. Presently, the PLP produces the best results for point-source targets. [Copyright &y& Elsevier]

Abstract: Vertically-resolved spectral characteristics of the Titanian haze in the 2-μm wavelength range were derived from solar occultation spectra measured by Cassini/VIMS on January 15, 2006. At the various altitudes probed by the solar occultation measurements, we reproduced the observed spectra using a radiative transfer program including absorption by CH4 ro-vibrational bands, collision-induced absorption by N2–N2 pairs, and H2–N2 dimers, as well as absorption and scattering by the haze particles. The retrieved optical depth spectra (or τ-spectra) for the haze show marked variations in the 2.1–2.8μm range, with peaks near 2.30 and 2.35μm, and the relative amplitude of these peaks changing with altitude. The gross spectral shape of the τ-spectra is found similar to the typical 2-μm absorption spectra of the alkane group of hydrocarbon (C n H2n+2) ices. The τ-spectra retrieved at 2μm and those previously retrieved at 3μm by Kim et al. (2011) are simultaneously reproduced by combinations of 2- and 3-μm absorbance spectra of alkane ices such as CH4, C2H6, C5H12, C6H14, with the addition of a nitrile ice, CH3CN. These combinations are neither unique nor limited and need more fine-tuning to fit the detailed features of the τ-spectra. There is a need for additional laboratory measurements of absorbance and indices of refraction for a wider variety of hydrocarbon and nitrile ices in the temperature range relevant to Titan. [Copyright &y& Elsevier]

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]

We have obtained Gemini/GNIRS 3.3–3.4 μm spectra of Jupiter at 65o North latitude over a range of longitudes roughly centered on the 8-μm CH 4 north polar hot spot (8CNPHS). The spectra were measured on four occasions during a four-month period in 2018, in order to search for variability of the 3-μm emissions of CH 4 and C 2 H 6. The observed locations of the brightest spots of the C 2 H 6 and CH 4 emissions at 65oN differed in longitude typically by 20o during this period. The peak emission intensities of these species showed large variations, with the highest intensities 3–4 times greater than the lowest intensities. In addition, the brightest 3-μm CH 4 emissions and hottest temperatures at the 8CNPHS were significantly less than those at the 3-μm CH 4 north polar hot spot (3CNPHS, Kim et al., 2015). Recently, Sinclair et al. (2019) reported a coincidence between solar wind dynamical pressure and the 8-μm brightening of the 8CNPHS. In contrast, we find lack of correlation in our data between the 3-μm hydrocarbon emission intensities at the 8CNPHS and the solar wind strength. We also find lack of correlation between H 3 + intensities and the solar wind strength during the period. However, due to the limited observational data, it is too early to conclude whether this lack of correlation indicates that the solar wind activity induced no significant changes in local temperatures (<40 K) and/or mixing ratios of these molecules. Our observing period was close to the historic grand solar minimum. The detailed influence of the solar activity on the 3 and 8 μm brightness at the 8CNPHS is not quantitatively understood at the present time. • Gemini/GNIRS 3.3–3.4 μm spectra of the 8-μm CH 4 north polar hot spot (8CNPHS) of Jupiter were obtained. • Four occasions during a five-month period in 2018 were observed. • The variability of the 3-μm emission intensities of CH 4 , C 2 H 6 , and H 3 + was studied. • The peak intensities of these species showed the highest 3–4 times greater than the lowest. • We find lack of correlation between the 3-μm hydrocarbon intensities at the 8CNPHS and the solar wind strength. [ABSTRACT FROM AUTHOR]

• GO approximation is applied to light scattering from media consisting of 3-foci transparent ellipsoids. • Phase functions of Mueller matrix elements of the media are computed with ray-tracing technique. • Phase functions of different scattering orders (until 5) including internal reflections were calculated. • Strong backscatter is mainly formed inside particles with one or two internal reflections. We study light scattering by non-spherical Maxwell particles and media consisting of them using computer simulations. The particle shapes are defined by a generalization of the concept 3-foci ellipses introduced by J. C. Maxwell. We modify them for the 3-D case by replacing the distances between the foci and current points on the ellipsoid surface by their logarithms. This makes it possible to describe 3-D ellipsoids that have partially concave surfaces. We carry out simulations within the framework of geometrical optics based on reflection and refraction of 108 rays and calculate phase curves of the nonzero elements of the Mueller matrix. This enables us to clarify the origin of the characteristics of the phase curves, i.e., which scattering order is responsible for the curve features. It is shown that equality M 12 = M 21 and M 34 = – M 43 that are valid for isolated particles are broken by the interactions with neighboring particles. It is also shown that the opposition effect of such particulate surfaces is mainly formed by components having one or more internal reflections within particles. [ABSTRACT FROM AUTHOR]

We carried out multi-band (B, V, and R bands) polarimetric measurements of several soil samples targeted for the lunar regolith (JSC-1A, Fe 2 O 3 , SiC, and JSC-1Mars). Our laboratory experiments are intended to provide some constraints to the theoretical and numerical studies of the light scattering off the particulate surface of airless bodies in the solar system. Among our samples, the lunar soil simulant JSC-1A has the closest α max to the typically observed value on the lunar surface, ∼100 ° , where α max is the phase angle at which the polarization has the maximum value. In the other samples, α max is higher than 120 ° or significantly wavelength dependent. The empirical relationship between the grain size, maximum polarization and albedo for the lunar regolith overestimates the actual grain sizes of some of our samples by a factor of up to ∼6. The measured polarization degrees and albedos of the JSC-1A sample are similar to the typical observed values of the lunar maria. We also find that the wavelength dependence of both polarization degree and albedo is larger for smaller-grain samples. [ABSTRACT FROM AUTHOR]