Detailed Analysis of the Intra-Ejecta Dark Plains of Caloris Basin, Mercury

The Caloris basin on Mercury is floored by light-toned plains and surrounded by an annulus of dark-toned material interpreted to be ejecta blocks and smooth, dark, ridged plains. Strangely, preliminary crater counts indicate that these intra-ejecta dark plains are younger than the light-toned plains within the Caloris basin. This would imply a second, younger plains emplacement event, possibly involving lower albedo material volcanics, which resurfaced the original ejecta deposit. On the other hand, the dark plains may be pre-Caloris light plains covered by a thin layer of dark ejecta. Another alternative to the hypothesis of young, dark volcanism is the possibility that previous crater counts have not thoroughly distinguished between superposed craters (fresh) and partly-buried craters (old) and therefore have not accurately determined the ages of the Caloris units. This abstract outlines the tasks associated with a new mapping project of the Caloris basin, intended to improve our knowledge of the geology and geologic history of the basin, and thus facilitate an understanding of the thermal evolution of this region of Mercury

A synthesis of Martian aqueous mineralogy after 1 Mars year of observations from the Mars Reconnaissance Orbiter

Martian aqueous mineral deposits have been examined and characterized using data acquired during Mars Reconnaissance Orbiter's (MRO) primary science phase, including Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral images covering the 0.4–3.9 μm wavelength range, coordinated with higher–spatial resolution HiRISE and Context Imager images. MRO's new high-resolution measurements, combined with earlier data from Thermal Emission Spectrometer; Thermal Emission Imaging System; and Observatoire pour la Minéralogie, L'Eau, les Glaces et l'Activitié on Mars Express, indicate that aqueous minerals are both diverse and widespread on the Martian surface. The aqueous minerals occur in 9–10 classes of deposits characterized by distinct mineral assemblages, morphologies, and geologic settings. Phyllosilicates occur in several settings: in compositionally layered blankets hundreds of meters thick, superposed on eroded Noachian terrains; in lower layers of intracrater depositional fans; in layers with potential chlorides in sediments on intercrater plains; and as thousands of deep exposures in craters and escarpments. Carbonate-bearing rocks form a thin unit surrounding the Isidis basin. Hydrated silica occurs with hydrated sulfates in thin stratified deposits surrounding Valles Marineris. Hydrated sulfates also occur together with crystalline ferric minerals in thick, layered deposits in Terra Meridiani and in Valles Marineris and together with kaolinite in deposits that partially infill some highland craters. In this paper we describe each of the classes of deposits, review hypotheses for their origins, identify new questions posed by existing measurements, and consider their implications for ancient habitable environments. On the basis of current data, two to five classes of Noachian-aged deposits containing phyllosilicates and carbonates may have formed in aqueous environments with pH and water activities suitable for life

A roadmap for planetary caves science and exploration

2 páginas.- 1 figura.- 16 referenciasTo the Editor — 2021 is the International Year of Caves and Karst. To honour this occasion, we wish to emphasize the vast potential embodied in planetary subsurfaces. While researchers have pondered the possibility of extraterrestrial caves for more than 50 years, we have now entered the incipient phase of planetary caves exploration....Peer reviewe

Analysis of enigmatic structures on Mars and Venus and implications for crustal history

The crustal history of two structurally complex areas on two different planetary bodies is explored, using a combination of image and topographic analysis, kinematic mapping and numerical modeling. Throughout the polygonal terrain of Utopia Planitia, Mars are found circular grabens that are inferred to overlie the rims of buried impact craters. The correspondence of circular grabens and polygonal terrain suggests that their formation may be intrinsically linked. A topographic analysis of circular grabens shows that they bound topographic depressions whose surface relief scales directly with diameter, consistent with a model of polygon formation dependent upon a “wet” cover material. A model is presented for why the circular grabens are sometimes comprised of two nested ring fractures. The model results imply that cover material in the southwestern polygonal area of Utopia may range from 1–2 km thick and strongly favors a wet sedimentary origin for the cover material. A systematic study of the topography of quasi-circular depressions (QCDs) around the Utopia Basin is presented. The results of this study support the assumption that QCDs are the surface representations of buried impact craters. There are ridges radial to Irnini Mons, Venus, revealed by high resolution mapping at 75 m/pixel. Unlike the unit of arcuate ridges directly south, these ridges are on top of the Irini flows and cannot be an older feature. Analytical modeling of the perturbation of regional stresses around a pressurized magma chamber conduit shows that in the presence of the regional north-south compression, responsible for the regional set of east-west trending wrinkle ridges, circumferential stresses can be compressive. Directional models of Venus\u27 tectonic history argue that all wrinkle ridge formation occurred prior to the formation of large volcanoes. Thus, continuing the regional compression that formed the wrinkle ridges through the volcano building event contradicts directionalism and supports non-directional tectonic models