157 research outputs found
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 sizeâfrequency 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 CSFDâcrater 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 steepâsloped production CSFDs, such as Imbrian to Eratosthenianâera 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 âcookie cutting.â Cookie cutting is most clearly observed on lunar terrains dominated by large craters with shallowâsloped production CSFDs, such as the preâNectarian lunar highlands. We use the Cratered Terrain Evolution Model (CTEM) to simulate the evolution of a preâNectarian surface unit. The model was previously used to simulate the diffusionâinduced 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 perâcrater contribution to degradation by small simple and large complex craters
An advanced thermal roughness model for airless planetary bodies. Implications for global variations of lunar hydration and mineralogical mapping of Mercury with the MERTIS spectrometer
We present a combined reflectance and thermal radiance model for airless planetary bodies. The Hapke model provides the reflected component. The developed thermal model is the first to consistently use rough fractal surfaces, self-scattering, self-heating, and disk-resolved bolometric albedo for entire planets. We validated the model with disk-resolved lunar measurements acquired by the Chinese weather satellite Gaofen-4 at around 3.5â4.1 ÎŒm and measurements of the Diviner lunar radiometer at 8.25 ÎŒm and 25â41 ÎŒm, finding nearly exact agreement. Further, we reprocessed the thermal correction of the global lunar reflectance maps obtained by the Moon Mineralogy Mapper M3 and employed the new model to correct excess thermal radiance. The results confirm the diurnal, latitudinal, and compositional variations of lunar hydration reported in previous and recent studies with other instruments. Further, we compared the model to lunar measurements obtained by the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) on board BepiColombo during a flyby maneuver on April 9, 2020: the measured and the modeled radiance variations across the disk match. Finally, we adapted the thermal model to Mercury for emissivity calibration of upcoming Mercury flyby measurements and in-orbit operation. Although a physical parameter must be invariant under various observation scenarios, the best lunar surface roughness fits vary between different datasets. We critically discuss possible reasons and conclude that anisotropic emissivity modeling has room for improvement and requires attention in future studies
Lithologic Mapping of HED Terrains on Vesta using Dawn Framing Camera Color Data
The surface composition of Vesta, the most massive intact basaltic object in
the asteroid belt, is interesting because it provides us with an insight into
magmatic differentiation of planetesimals that eventually coalesced to form the
terrestrial planets. The distribution of lithologic and compositional units on
the surface of Vesta provides important constraints on its petrologic
evolution, impact history and its relationship with Vestoids and
howardite-eucrite-diogenite (HED) meteorites. Using color parameters (band tilt
and band curvature) originally developed for analyzing lunar data, we have
identified and mapped HED terrains on Vesta in Dawn Framing Camera (FC) color
data. The average color spectrum of Vesta is identical to that of howardite
regions, suggesting an extensive mixing of surface regolith due to impact
gardening over the course of solar system history. Our results confirm the
hemispherical dichotomy (east-west and north-south) in albedo/color/composition
that has been observed by earlier studies. The presence of diogenite-rich
material in the southern hemisphere suggests that it was excavated during the
formation of the Rheasilvia and Veneneia basins. Our lithologic mapping of HED
regions provides direct evidence for magmatic evolution of Vesta with diogenite
units in Rheasilvia forming the lower crust of a differentiated object.Comment: Accepted for Meteoritics and Planetary Science special issue for
Composition of Vesta/Dawn Missio
A review of issues and challenges
Determining the ages of young planetary surfaces relies on using populations
of small, often sub-km diameter impact craters due to the higher frequency at
which they form. Smaller craters however can be less reliable for estimating
ages as their size-frequency distribution is more susceptible to alteration
with debate as to whether they should be used at all. With the current
plethora of meter-scale resolution images acquired of the lunar and Martian
surfaces, small craters have been widely used to derive model ages to
establish the temporal relation of recent geologic events. In this review
paper, we discuss the many factors that make smaller craters particularly
challenging to use and should be taken into consideration when crater counts
are confined to small crater diameters. Establishing confidence in a model age
ultimately requires an understanding of the geologic context of the surface
being dated as reliability can vary considerably and limitations of the dating
technique should be considered in applying ages to any geologic
interpretation
A shock recovery experiment and its implications for Mercury's surface : The effect of high pressure on porous olivine powder as a regolith analog
We conducted classic dynamic high - pressure experiments on porous San Carlos (SC) olivine powder to examine if and how different shock stages modify corresponding reflectance mid â infrared (MIR) spectra. Microscopic investigation of the thin sections produced of our shocked samples indicates local peak pressures of >60 GPa along with all lower grade shock stages. Spectral analyses of optically identified shock areas were documented and compared in terms of Christiansen Feature (CF) and the position of olivine â diagnostic Reststrahlenbands (RBs). We found that one RB (fundamental vibrations of the orthosilicate - ion) of olivine occurring at 980 cmâ1 (corresponding to â 10.2 ÎŒm) shows the least energetic shift in the investigated MIR spectra and could therefore serve as a proxy for the presence of olivine in remote sensing application. Furthermore, a peak located at â 1060 cmâ1 (â 9.4 ÎŒm) shows a significant intensity change probably related to the degree of shock exposure or grain orientation effects, as we observe a decline in intensity of this band from our averaged reference olivine spectra of our IRIS database (diffuse reflectance measurement) down to spectra of grains showing mosaicism and recrystallized areas. We also report the presence of a weak band in some of the olivine spectra located at â 1100 cmâ1 (9.1 ÎŒm) that has an influence on the position of the CF when spectral data of olivine are averaged.Peer reviewe
Characterization of High-priority Landing Sites for Robotic Exploration Missions in the Apollo Basin, Moon
The South PoleâAitken (SPA) basin is the oldest and largest visible impact structure on the Moon, making it a high priority science site for exploration missions. The 492 km diameter Apollo peak-ring basin is one of the youngest and largest basins within the SPA basin. We selected three regions of interest (ROIs) in the Apollo basin for which the landing and operational hazards are minimized and evaluated their science and in situ resource utilization (ISRU) potential. We examined topography, slope, crater density, rock abundance, geologic mapping, mineralogy, and inferred subsurface stratigraphy within each ROI. The results show that the terrain is safe for landing without precision landing (within a few hundred meters). The mare materials have high ISRU potential with relatively high FeO (âŒ16â20 wt%) and TiO2 (âŒ3â10 wt%) contents. Two robotic exploration mission architectures were examined for their scientific potential: (1) lander and rover with a dedicated payload suite and (2) the same architecture with sample return capability. In situ observations can address six of seven National Research Council concepts (1â3, 5â7) and Campaigns 1 and 5 of the European Space Agency's Strategy for Science at the Moon
Science-rich Sites for In Situ Resource Utilization Characterization and End-to-end Demonstration Missions
Within the European Space Agencyâs âCommercial In Situ Resource Utilization (ISRU) Demonstration Mission Preparation Phase,â we examined two types of lunar sites in preparation for an ISRU demonstration mission. First, we considered poorly characterized potential resource sites. For these so-called characterization sites, precursor missions would investigate the material properties and address strategic knowledge gaps for their use as ISRU feedstock. Regions of interest for characterization missions include the Aristarchus plateau, Montes Harbinger/Rimae Prinz, Sulpicius Gallus, and Rima Bode. Regional pyroclastic deposits at the Aristarchus plateau and adjacent Montes Harbinger/Rimae Prinz exhibit remotely sensed low-Ti, high-Fe2+ compositions. They differ from the high-Ti pyroclastics at Rima Bode and Sulpicius Gallus, which are similar to the pyroclastics northwest of the Taurus Littrow valley (Apollo 17 site). Thus, exploration of the Aristarchus plateau would allow investigation of previously uncharacterized materials, whereas Rima Bode or Sulpicius Gallus would allow comparison to Apollo 17 pyroclastics. Any of these sites would enable evaluation of reported H2O/OH in these deposits. Second, we examined a possible site for a direct ISRU demonstrator mission. For a stand-alone end-to-end (E2E) ISRU demonstrator, a fuller understanding of the physical and compositional characteristics of potential feedstock is required for mission risk reduction. In this case, locations near preexisting sites would allow extrapolation of ground truth to nearby deposits. Because a Ti-rich pyroclastic deposit appears advantageous from beneficiation and compositional perspectives, we examine an example E2E demo site northwest of the Taurus Littrow valley. Hydrogen and methane reduction, as well as the FrayâFarthingâChen Cambridge process, could be tested there.BMWi, 50OW1504, MissionsunterstĂŒtzende Arbeiten und geologische Untersuchungen der lunaren OberflĂ€che mit Daten der Lunar Reconnaissance Orbiter Camera (LROC)BMWi, 50OW2001, MissionsunterstĂŒtzende und wissenschaftliche Arbeiten mit Daten der Lunar Reconnaissance Orbiter Camera (LROC) und Vorbereitung zukĂŒnftiger Mondmissione
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