Degradation of small simple and large complex lunar craters: Not a simple scale dependence

The crater record of a planetary surface unit is often analyzed by its cumulative size‐frequency distribution (CSFD). Measuring CSFDs involves traditional approaches, such as traditional crater counting (TCC) and buffered crater counting (BCC), as well as geometric corrections, such as nonsparseness correction (NSC) and buffered nonsparseness correction (BNSC). NSC and BNSC consider the effects of geometric crater obliteration on the CSFD. On the Moon, crater obliteration leads to two distinct states in which obtained CSFDs do not match the production CSFD—crater equilibrium and nonsparseness. Crater equilibrium occurs when each new impact erases a preexisting crater of the same size. It is clearly observed on lunar terrains dominated by small simple craters with steep‐sloped production CSFDs, such as Imbrian to Eratosthenian‐era mare units. Nonsparseness, on the other hand, is caused by the geometric overlap of preexisting craters by a new impact, which is also known as “cookie cutting.” Cookie cutting is most clearly observed on lunar terrains dominated by large craters with shallow‐sloped production CSFDs, such as the pre‐Nectarian lunar highlands. We use the Cratered Terrain Evolution Model (CTEM) to simulate the evolution of a pre‐Nectarian surface unit. The model was previously used to simulate the diffusion‐induced equilibrium for small craters of the lunar maria. We find that relative to their size, large craters contribute less to the diffusion of the surrounding landscape than small craters. Thus, a simple scale dependence cannot account for the per‐crater contribution to degradation by small simple and large complex craters

A Fresh Look at the Stratigraphy of Northern Australe

The roughly circular collection of mare deposits centered at ~38.9S, 93E is often re- ferred to as Mare Australe. It is located outside of the Procellarum KREEP Terrain. The circular arrangement of Australes mare patches has suggested an ancient, heavily degraded or relaxed impact basin roughly 900 km in diameter. The mare deposits are generally thought to have erupted into smaller post- basin craters. The type, volume, and distribution of mare eruptions potentially resembles the early stages of basin-filling mare events, but which are preserved in Australe and some farside locations. Gravity data suggest that if there was a basin, it is much smaller than originally proposed (now ~600 km) and located in the northern part of Mare Australe, between Humboldt, Milne, and Jenner craters. As a whole, Mare Australe lacks the topography typically associated with a basin; however, northern Australe has a slight topographic depression that roughly corresponds to the basin-like Bouguer gravity signature in the same area. The compositions exposed in Humboldt crater suggest that a preexisting basin might have excavated deeper crustal material. However, the underlying cause of the circularity of Mare Australes deposits, particularly those extending outside of the potential impact basin setting, is not yet understood. Thus, Australe may preserve fundamental information about mare volcanism potentially uncoupled from basin formation and structure. The objectives of this study are to use new high- resolution data (images, gravity, topography, and com- position) to reassess Australes mare deposits, deter- mine the timing and style of volcanism, identify discrete basalt deposits, and to further characterize the evolution of magmatism and subsurface structure in this area. Here, we focus on the northern Australe deposits (between Humboldt, Jenner, and Milne). As originally noted by Whitford-Stark (1979), Humboldt crater and its ejecta make an excellent stratigraphic marker that can be traced across much of the Australe region. The ejecta serves as a stratigraphic constraint for absolute model ages (AMAs) derived from crater size-frequency distributions (CSFDs)

Ventricular assist device implantation in the elderly

BACKGROUND: Dramatic advances in ventricular assist device (VAD) design and patient management have made mechanical circulatory support an attractive therapeutic option for the growing pool of elderly heart failure patients. METHODS: A literature review of all relevant studies was performed. No time or language restrictions were imposed, and references of the selected studies were checked for additional relevant citations. RESULTS: In concordance with the universal trend in mechanical circulatory support, continuous flow devices appear to have particular benefits in the elderly. In addition, the literature suggests that early intervention before the development of cardiogenic shock, important in all patients, is particularly paramount in older patients. CONCLUSIONS: The ongoing refinement of patient selection, surgical technique, and post-operative care will continue to improve surgical outcomes, and absolute age may become a less pivotal criterion for mechanical circulatory support. However, clear guidelines for the use of mechanical circulatory support in the elderly remain undefined

Re-examination of the Population, Stratigraphy, and Sequence of Mercurian Basins: Implications for Mercurys Early Impact History and Comparison with the Moon

Mercury has one of the best preserved impact records in the inner Solar System due to the absence of an atmosphere, but it has much higher rates of surface modification than on the Moon. The earliest geological mapping of the planet revealed a variety of important differences from the Moon, regarding the impact basin (D 300 km) and cratering record, as well as the extensive volcanic plains of Mercury [1-3]. It has been shown [3] that the bombardment history of the terrestrial planets is lunar-like and linked in terms of impactor population(s) and impact rates. Recent studies suggest that Mercury and the Moon had the same early impactor populations based on the similarity of their crater size-frequency distributions (CSFD), however the impact rates on Mercury are higher than on the Moon. Catalogued and characterized the basin population on Mercury using early optical data obtained by the MESSENGER spacecraft and found 46 certain and probable impact basins, as well as 41 tentative

A Study of Thermal Expansion on the Predicted Mercury Surface Minerals: Preparing for MERTIS on BepiColombo

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission unveiled that most of the detectable surface of Mercury is constituted by low-Fe and Mg-rich basalts [1,2], dismissing the previously assumed widespread presence of more felsic materials - as on the Moon’s surface. In this background, the BepiColombo mission will be fundamental to reveal the residual igneous crust of the Mercury surface, in order to assess its petrogenesis. The Mercury Radiometer and Thermal Infrared Spec¬trometer (MERTIS) on BepiColombo will be able to provide thermal infrared (TIR) emissivity spectra from 7 to 14 μm. This wavelength range is very useful to identify the structural properties of several silicates, and the position of the emissivity bands provides hints on the solid solutions. In addition to space-weathering degradation and impact-induced structural modifications, the thermal expansion driven by the daily tem¬perature variation of the surface of Mercury significantly affects the crystal structure and density of the present minerals and, consequently, their thermal infrared spectral signature. This behaviour has been recently demonstrated for several common terrestrial mineralogical phases [3,4,5], and could be even predicted for other silicates. A more difficult interpretation of the spectra arises, of course, from the simultaneous presence of different minerals, each one with its characteristic thermal expansion coefficient. In addition to the temperature-dependent spectral variations of single constituents (e.g. plagioclases, olivine, pyroxenes), the DLR Planetary Emissivity Laboratory (PEL) is measuring emissivity spectra of linear mixtures that most likely could be present on the surface of Mercury. To this aim, spectra of binary compositions (e.g., anorthosite, gabbro) and their single-phase components are measured along the MERTIS wavelength range in vacuum from low to high-temperatures - up to 450°C