The surfaces of the large uranian satellites are characterized by a mixture of H2O ice and a dark, potentially carbon-rich, constituent, along with CO2 ice. At the mean heliocentric distance of the uranian system, native CO2 ice should be removed on timescales shorter than the age of the Solar System. Consequently, the detected CO2 ice might be actively produced. Analogous to irradiation of icy moons in the Jupiter and Saturn systems, we hypothesize that charged particles caught in Uranus' magnetic field bombard the surfaces of the uranian satellites, driving a radiolytic CO2 production cycle. To test this hypothesis, we investigated the distribution of CO2 ice by analyzing near-infrared (NIR) spectra of these moons, gathered using the SpeX spectrograph at NASA's Infrared Telescope Facility (IRTF) (2000-2013). Additionally, we made spectrophotometric measurements using images gathered by the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope (2003-2005). We find that the detected CO2 ice is primarily on the trailing hemispheres of the satellites closest to Uranus, consistent with other observations of these moons. Our band parameter analysis indicates that the detected CO2 ice is pure and segregated from other constituents. Our spectrophotometric analysis indicates that IRAC is not sensitive to the CO2 ice detected by SpeX, potentially because CO2 is retained beneath a thin surface layer dominated by H2O ice that is opaque to photons over IRAC wavelengths. Thus, our combined SpeX and IRAC analyses suggest that the near-surfaces (i.e., top few 100 mu m) of the uranian satellites are compositionally stratified. We briefly compare the spectral characteristics of the CO2 ice detected on the uranian moons to icy satellites elsewhere, and we also consider the most likely drivers of the observed distribution of CO2 ice. (C) 2015 Elsevier Inc. All rights reserved.

In this study we examine a lunar pyroclastic deposit (LPD) identified using LROC WAC images, Selene-1 (Kaguya) and Clementine multispectral data, the Chandryann-1's Moon Mineralogy Mapper (M-3), and the LROC WAC-based GLD100 DTM. Selene-1 (Kaguya) and Clementine albedo imagery indicates the presence of pyroclastic deposits located some 40 km to the west-southwest of the crater Yangel in Mare Vaporum, and to the southeast of Sinus Fidel (16.42 degrees N and 3.26 degrees E), and associated with a dome like structure. This dome, which we term Yangel 1 (Ya1), lies immediately to the south of a mare flooded crater which is approximately 7.5 km in diameter, and is partially buried along its southern rim by the domes northern flank. With a diameter of 5.2 km, and a height of 620 m, the dome Ya1 exhibits evidence of pyroclastic volcanic deposits, both on its surface and peripherally. The current study discusses the dome Ya1, the associated deposits and possible relationship between them. (C) 2014 Elsevier Ltd. All rights reserved.

We present a study of the Lavoisier lunar crater combining photometric data from the AMIE camera (SMART-1 mission) and hyperspectral data from the Moon Mineralogy Mapper M-3 (Chandrayaan-1 mission), with a special emphasis on the pyroclastic deposits considered to be present on the crater floor. The photometric parameters are in agreement with the general photometric behaviors of the lunar regolith, especially the backscattering properties. The assumed pyroclastic materials within Lavoisier present at first order a rather homogeneous photometric behavior, in favor of their surface state homogeneity. However, they are not significantly different from other non-dark patches on the crater's floor, whereas the assumed pyroclastic deposit of Lavoisier F displays clearly different photometric parameters, indicative of distinct physical surface properties from the pyroclastic materials within Lavoisier. Using laboratory data to get hindsight on the reliability of results from orbital datasets, we show that the use of more or less depleted phase curves for photometric inversions has a clear impact on the photometric parameters that are derived. The hyperspectral analysis of Lavoisier crater shows that the various pyroclastic deposits present the same mineralogical composition, distinct from the floor of the crater and the mare basalts. M-3 spectra do not differentiate between the pyroclastic deposits within Lavoisier and Lavoisier F. They have the same spectral signatures, share a similar mineralogical composition, and probably the same volcanic origin. Therefore, the differences seen in the photometric analysis from the AMIE observations are indicative of variations in grain sizes, and/or roughness, and/or particles scattering properties, and/or compaction state. The combined mineralogical and photometric analysis is a very useful approach to document the nature of the pyroclastic deposits of the Moon, and possibly of other objects of the Solar System (e.g., Mercury) as the combination of the mineralogy and the physical properties sets constraints on the origin and mode of emplacement of the deposits, and characterizes the eruption styles. (C) 2013 Elsevier Inc. All rights reserved.

In this study we examine a lunar volcanic region near Doppelmayer, composed of two domical structures previously not studied in detail and a well-known lunar pyroclastic deposit. Dome 1 is situated at selenographic coordinates 41.92 degrees W and 30.08 degrees S, dome 2 at 43.42 degrees W and 30.66 degrees S. We perform a spectrophotometric study of representative locations of the volcanic region based on Clementine UVVIS data. Relying on ground-based high-resolution CCD imagery, we furthermore examine the morphometric characteristics of the two domes, making use of a combined photoclinometry and shape from shading technique. Based on a rheologic model, we examine the physical conditions under which the domes were formed. Dome 1 is spectrally atypically red for mare domes and shows a very weak mafic absorption, implying a low TiO2 and FeO content. The overall spectral signature corresponds to that of a mixture between mare and highland soils. Dome 1 was formed of lava with a relatively high viscosity value of similar to 10(7) Pas, situated between the ranges of values typically observed for mare domes and for the Gruithuisen and Mairan highland domes, respectively, erupting at moderate rates over a long period of time. Dome 1 is larger, steeper, and more voluminous than typical mare domes but has a much lower flank slope than the Gruithuisen and Mairan highland domes. It is an exemplar of a rare type of unusually steep and voluminous mare domes, similar to the well-known mare domes Hortensius 5 and 6 and Herodotus omega. We discuss the relevance of vertical (assimilation of crustal material) vs. lateral (distribution of material across mare-highland boundaries by random impacts) mixing mechanisms as being responsible for the observed spectral appearance of dome 1. The thermal conditions in the lunar interior did not favour the assimilation of crustal wallrock into the ascending magma. Due to the fact that dome 1 is located right on the boundary between hummocky terrain and a mare pond, lateral mixing of mare and highland soils is a much more natural explanation for the observed spectral signature. For dome 2, we find that it is a typical effusive mare dome, given its spectral and morphometric properties and inferred rheologic parameters. An estimation of the dimensions of the feeder dikes of the two domes reveals that the dike which formed dome I was five times as broad as the one which formed dome 2, while the dike lengths only differ by about one third. The dike dimensions suggest that their source regions were located below the lunar crust. (c) 2006 Elsevier Ltd. All rights reserved.

The program for lunar surface texture analysis with imaging polarimetry conducted at Observatoire de Paris included the large crater Langrenus near the lunar limb. When making the relevant observations, bright features were discovered near the Langrenus central peak. They appeared in both the photographic images and the polarigraphic images, on which they evolved simultaneously. Very few cases of so-called lunar transient phenomena have been reported in the past; they were diverse and controversial. Most of the visual apparitions were described as short-duration flashes. None of them were suggestive of the slowly evolving effect presently observaed. The brightness enhancements produced a simultaneous increase of polarized light. Such a dependance is not compatible with reflectivity variations at the solid surface of the Moon, which should associate brightness increases with polarization decreases. It does not agree with incandescence and with flashing discharges, which do not produce polarized light. Specular reflection on properly oriented relief slopes may increase the brightness and the polarization simultaneously, but the process can hardly explain the amplitude of the enhancments observed. Particles erupted by volcanic processes such as fire fountaining should leave after the active phases, a deposition of dark material at the lunar surface, which is not observed. It is clusters of hills made of a bright material that are present at the event emplacements. The simultaneous increase of brightness and of polarization is consistant with light scattering on clouds made of separated grains. Small bright highland soil grains may be levitated above the lunar surface by outgassing from the lunar interior. The events occurred at the border of a mare basin, near the central peak of a large crater, in a terrain presumed to be particularly fractured and fissured. The intense radon emanation that was measured around the site with the Apollo orbital instruments indicates gas release from the lunar interior, and supports the interpretation of the brightening events as soil grains levitated by the degassing. (C) 2000 Academic Press.