Mare Australe Research Articles

Fast Magnetization Vector Inversion Method with Undulating Observation Surface in Spherical Coordinate for Revealing Lunar Weak Magnetic Anomaly Feature

The three-dimensional magnetic vector structure (magnetization intensity and direction) of the planet can be effectively used to analyze the characteristics of its formation and operation. However, the quick acquisition of a large region of the magnetic vector structure of the planet with bigger observation surfaces undulation is hard and indispensable. We firstly proposed a fast magnetization vector inversion method for the inversion of a magnetic anomaly with the undulating observation surfaces in the spherical coordinate system, which first transforms the data to a plane when the data are distributed on a surface. Then, it uses a block-Toeplitz-Toeplitz-block (BTTB)-FFT to achieve fast inversion with the constraint that the magnetization intensities of the grids between the transformed observation surfaces and the terrain are zero. In addition, Gramian constraint term is used to reduce the ambiguity of the magnetic vector inversion. The theoretical model tests show that the proposed method can effectively improve the computational efficiency by 23 times in the 60 × 60 × 10 grid division compared to the conventional inversion method, and the accuracy of the two computation methods is comparable. The root-mean-square error of the magnetization intensity is only 0.017, and the angle error is within 1°. The magnetization vector structure shows that the largest crater diameter does not exceed 340 km in the Mare Australe region, the amplitude of the magnetic anomaly is much higher than the current meteorite impact simulation results, and the depth of the magnetic source is less than 10 km, which cannot be explained by the impact simulation experiments. In addition, the magnetization directions of adjacent sources differ by 122° (or 238°), and the high-frequency dynamics of the Moon as well as the short-lived dynamics may be responsible for this phenomenon. The magnetization directions of the three adjacent sources in the Mare Crisium region are close to each other and differ in depth with different cooling times, making it difficult to record the transient fields produced by meteorite impacts. In addition to the above characteristics, the magnetization direction of the magnetic sources in both regions is uniformly distributed without reflecting the dispersion of the magnetization direction of the meteorite impact magnetic field. Therefore, it can be inferred that the magnetic anomalies in these two regions are related to the generator hypothesis.

The Variability of Lunar Mare Basalt Properties from Surface Rock Abundance

We use the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment surface rock abundance data set to investigate how rock content changes with surface age in the maria. We find that surface rock abundance decreases with unit age as expected for a thickening regolith, but age alone cannot explain most of the observed regional variability in rock abundance. We propose that this additional variability is primarily caused by differences in the initial mare basalt properties such that some flows break down more readily than others. We calculate the best-fit relationship between the surface rock abundance and unit age and investigate the regional variability in the residual errors of this fit. Relative to this best-fit relationship, we find that Mare Humorum and parts of Oceanus Procellarum are anomalously rocky, and Mare Australe is rock-poor for its age. These regional differences, which cannot be explained by unit age, are likely due to variability in the initial properties of mare basalts.

Scaliger Crater Region on the Moon: Implications for the Australe North Basin and magmatism in the region

Australe North (35.5°S, 96°E) is a pre-Nectarian impact basin north of Mare Australe, first identified using the GRAIL data. It does not show clear topographic signatures typical of any large impact structure on the Moon. However, results from GRAIL (Gravity Recovery and Interior Laboratory) mission suggested the presence of a ∼ 880 km wide basin whose boundary does not coincide with the earlier identified Australe Basin. In this study, we investigate the Scaliger Crater region to understand the controls that the proposed Australe North Basin played on the local geology in the region. The location of the Scaliger Crater at the intersection of the rims of two pre-Nectarian Basins, Milne and the proposed Australe North provides a unique geological setting to reconstruct the region's geological history. We provide geological evidence substantiating the existence of the rim of the Australe North Basin, as has been proposed using gravity data. Based upon the spectral signatures and morphometry, we suggest the presence of a mafic pluton and/or lower crustal/mantle rocks in the region and provide constraints on its emplacement timescale. For the first time, Late-stage volcanism has been reported inside the Bowditch Crater and Lacus Solitudinis, emplaced at ∼1.7 Ga and ∼ 2.3 Ga, respectively, suggesting prolonged volcanism at the eastern lunar nearside-farside boundary inside an obscured pre-Nectarian basin.

Mach and Froude Numbers on Mars

Mars atmospheric global circulation models exhibit transonic jet streaks during northern winter, which motivates this study of the Mach number, Ma (the ratio of flow speed to the speed of sound), and Froude number, Fr (the ratio of flow speed to the speed of buoyancy waves), as a function of season and location. Two global reanalyses spanning Mars Years (MY) 24 to 32 are used as input, EMARS and OpenMARS. The study’s vertical coordinate is potential temperature, θ, ranging from θ = 400 to 1100 K (from z ≈ 32 to 66 km); the floor is set to the lowest level that avoids intersecting mountains. Area-weighted global means and standard deviations and 5 yr temporal means using the complete years MY 25, 26, 29, 30, and 31 are compared. EMARS and OpenMARS show general agreement below θ = 700 K (z ≈ 53 km), where the observational constraints are strongest, but can vary significantly at higher levels. Both reanalyses contain transonic jet streaks in every northern winter sampled. The Fr signal is roughly twice the Ma number signal, as expected where the temperature lapse rate is small compared to the dry adiabatic lapse rate. Mach numbers are similar in both reanalyses but show larger year-to-year variability in OpenMARS. Maps of standard deviations indicate a depression between the main peaks in Tharsis and higher variability in Mare Boreum than Mare Australe. The main conclusion is that the atmosphere of Mars routinely operates in the compressible regime (0.3 < Ma < 0.8), unlike Earth. Aspects of all flow-speed meteorology are discussed.

Lunar surface chemistry observed by the KAGUYA multiband imager

The abundance and distribution of oxides and Mg# (Mg/(Mg ​+ ​Fe) in mole percent) values are important for revealing the petrologic characteristics and evolutionary history of the Moon. In this work, new lunar surface chemistry maps, including Al2O3, CaO, FeO, MgO, TiO2, and Mg# maps, are generated from KAGUYA multiband imager (MI) spectra. These new maps are produced by the machine learning algorithm of the particle swarm optimization-support vector machine (PSO-SVM), and are characterized by relatively high accuracies and a high spatial resolution of 59 ​m/pixel, which are free to some degree from the topographic shadow effect. Moreover, Mg# values across the Moon exhibit an obvious chemical trichotomy. According to this Mg# feature, a new geological partition is suggested, and the lunar surface is divided into three geological units: the PM, SPAM, and FH units. The PM unit features low Mg# values, with an average of 0.55. The PM unit consists of Oceanus Procellarum, Grimaldi Crater, Tsiolkovskiy Crater, and some maria on the nearside and farside (e.g., the Frigoris, Imbrium, Tranquillitatis, Smythii, Crisium, Marginis, Orientale, and Moscoviense Maria). The FH unit possesses the highest Mg# values across the Moon, with an average of 0.70. The FH unit is composed of the Feldspathic Highlands Terrane (FHT), except for some maria (e.g., Orientale, Moscoviense, Australe, Marginis, and Smythii) and some craters (e.g., Tsiolkovskiy and Schickard). The SPAM unit is typical of medium Mg# values with an average of 0.65, and is constituted by the South Pole-Aitken Terrane (SPAT), Mare Australe, and some craters (e.g., the Schickard, Phocylides, Nasmyth, Schiller, and Inghirami Craters). The significant difference in Mg# values among the three geological units highlights the asymmetric magmatic evolution, crustal growth, and mare volcanism in the three units.

Fully Controlled 6 Meters per Pixel Mosaic of Mars's South Polar Region

AbstractThe Mars Reconnaissance Orbiter (MRO) spacecraft has been in operation around Mars since March 2006. The Context Camera (CTX), aboard MRO, has returned over 110,000 images of Mars at ≈5–6 m/px, providing nearly global coverage. Based on our work, reconstruction of MRO's orbit and camera pointing from ground tracking are offset from the Mars global coordinate system, with the 95th percentile of test points offset by ≈850 m, corresponding to ≈150 CTX pixels. While the original level of accuracy is potentially useful for some applications, providing relative control (image‐to‐image) and absolute or full control (image‐to‐ground reference) greatly improves the utility of the data. As a proof‐of‐concept, we have fully controlled all usable images of Mars Chart 30, Mare Australe, which is poleward of 65°S. This represents 4.7% of Mars's surface area and comprises 9,652 images (≈8% of the CTX catalog as of PDS release #48). The control was produced through a mixture of automated code and manual adjustment and validation, and mosaics were produced with manual input to provide a useful product with the best, most consistent images on top. The data—mosaics and updated SPICE kernels—are available to the community through NASA's Planetary Data System (PDS) Imaging and Cartography Annex. The workflow developed for this product is applicable to the remainder of Mars and other planetary bodies.

Mare Deposits Identification and Feature Analysis in Mare Australe Based on CE‐2 CELMS Data

AbstractThe microwave signal has the penetration capability, which provides a potential chance to improve understanding of the mare deposits and the formation process of Mare Australe, a complex, extensive, and poorly understood region on the Moon. In this paper, the Chang'E‐2 microwave radiometer (CELMS) data were selected and processed to evaluate the microwave thermal emission features of the mare deposits in Mare Australe. After comparison, the dTB map at 3.0 GHz is employed. The results are as follows. (a) The possible cryptomare is much more extensive in Australe region than that identified with optical data. (b) The basaltic volcanism is re‐understood as three major episodes. (c) The high dTB anomaly is interpreted as the location of the vent areas in the mare patches. (d) The K‐means algorithm was first used to process the CELMS data, and the identified linear and ring structures indicate some important information about the formation processes of Mare Australe. These special findings will be of fundamental significance to better understand the basaltic volcanism and the evolution of the lunar surface.

Provenance of Block Fields Along Lunar Wrinkle Ridges

AbstractBlock fields and associated relatively high reflectance material along wrinkle ridge summits are revealed in meter‐scale Lunar Reconnaissance Orbiter Camera images. Wrinkle ridges with block fields in Mare Australe, Crisium, Fecunditatis, Frigoris, Nubium, the northern half of Oceanus Procellarum, Serenitatis, and Tranquillitatis are evenly distributed, and block density generally increases with wrinkle ridge slope. The median cross‐sectional area (proxy for diameter) of the 1,368 blocks measured in this study is ~7 m2, and 75% of these blocks are ≤~14 m2. We propose that the largest variation in cross‐sectional area of the blocks is related to substrate physical properties of the mare basalt and not a function of the slope on which they occur, suggesting that physical properties rather than slope are a stronger control on block size. The maximum length of blocks may constrain the minimum basalt flow thickness or joint width; our block measurements suggest basalt flows ~2–14 m thick, agreeing with previous estimates. The data suggest that blocks originate from mare basalt layers that buckle and break as a result of movement along ridge‐forming thrust faults. High reflectance material associated with wrinkle ridge blocks likely represents freshly exposed rock and soil. Meter‐scale blocks may erode relatively quickly due to collisional disruption, indicating recent downslope movement of regolith exposing preexisting blocks or blocks formed and exposed by recent activity on ridge‐forming faults.

Multiple lithic clasts in lunar breccia Northwest Africa 7948 and implication for the lithologic components of lunar crust

AbstractThis study presents the petrography, mineralogy, and bulk composition of lunar regolith breccia meteorite Northwest Africa (NWA) 7948. We identify a range of lunar lithologies including basaltic clasts (very low‐titanium and low‐titanium basalts), feldspathic lithologies (ferroan anorthosite, magnesian‐suite rock, and alkali suite), granulites, impact melt breccias (including crystalline impact melt breccias, clast‐bearing impact melt breccias, and glassy melt breccias), as well as regolith components (volcanic glass and impact glass). A compositionally unusual metal‐rich clast was also identified, which may represent an impact melt lithology sourced from a unique Mg‐suite parent rock. NWA 7948 has a mingled bulk rock composition (Al2O3 = 21.6 wt% and FeO = 9.4 wt%) and relatively low concentrations of incompatible trace elements (e.g., Th = 1.07 ppm and Sm = 2.99 ppm) compared with Apollo regolith breccias. Comparing the bulk composition of the meteorite with remotely sensed geochemical data sets suggests that the sample was derived from a region of the lunar surface distal from the nearside Th‐rich Procellarum KREEP Terrane. Our investigations suggest that it may have been ejected from a nearside highlands‐mare boundary (e.g., around Mare Crisium or Orientale) or a cryptomare region (e.g., Schickard‐Schiller or Mare smythii) or a farside highlands‐mare boundary (e.g., Mare Australe, Apollo basin in the South Pole–Aitken basin). The distinctive mineralogical and geochemical features of NWA 7948 suggest that the meteorite may represent lunar material that has not been reported before, and indicate that the lunar highlands exhibit wide geological diversity.

Ilmenite mapping of the lunar regolith over Mare Australe and Mare Ingenii regions: An optimized multisource approach based on Hapke radiative transfer theory

AbstractWe model lunar ilmenite abundances over Mare Australe and Mare Ingenii regions using a new approach; we integrate Lunar Reconnaissance Orbiter Wide Angle Camera (WAC) and Clementine UV‐visible/near‐infrared (UVVIS/NIR) data to obtain a 14‐band mosaic (320‐2000 nm). We use Hapke's radiative transfer equations to compute spectra for various mixtures of orthopyroxene, clinopyroxene, plagioclase, olivine, and ilmenite, with varying grain size, chemistry, and degree of maturity, and find the closest match between the modeled spectra and the spectra of the less mature pixels (optical maturity ≥ 0.2) in the 14‐band mosaic. We calculate a “maximum stoichiometrically possible ilmenite content”, using Clementine‐derived TiO2 abundances and the amount of TiO2 in stoichiometric ilmenite, and use it as a constraint in our model. We validate our methodology with lunar soil spectra of known composition. Our results show that the integrated WAC‐UVVIS/NIR data and the UVVIS/NIR data overestimate ilmenite abundances by 8.80 wt % and 7.97 wt %, respectively, when a fixed maximum of 20 wt % ilmenite is used. When the maximum stoichiometrically possible ilmenite content is used as a constraint, the integrated WAC‐UVVIS/NIR data give slightly more accurate ilmenite abundance estimation (±2.87 wt %) than when using only UVVIS/NIR data (± 3.04 wt %). We find ilmenite concentrations of 0−11 wt % in Mare Australe and 0−6 wt % in Mare Ingenii region. Ilmenite abundances between 4 and 7 wt % are exposed in Mare Australe, whereas ilmenite abundances between 7 and 11 wt % are found on the walls of 0.6‐11.8 km diameter craters within Mare Australe.

Endogenic modification of impact craters on Mercury

Surface resolution of Mercury from Mariner-10 images is insufficient for identifying volcanic forms analogous to most of those on the moon. Consequently, other criteria must be used in order to assess the possibility of Mercurian volcanism. One criterion is the presence of internally modified impact craters similar to floor-fractured and mare-filled craters on the moon. Such craters typically occur near or within the lunar maria and exhibit features (fractures, shallow floors, dark-haloed craters, mare units) that either are resolvable at Mariner-10 resolutions or are detectable by indirect means, e.g., albedo and color contrasts. Mariner-10 images reveal several plausible examples, which, as on the moon, most commonly occur near plains-filled basins. The color-ratio images by Hapke, Danielson, Klaasen and Wilson indicate that some of the Mercurian craters exhibit red plains materials on their floors. Such distinctive units may correspond either to lavas analogous to mare basalts within certain lunar craters or to compositionally distinct subsurface material retained in the impact crater. Indicators used to recognize crater modification also can be used to recognize basin modification. Specifically, several basins exhibit photometric contrasts between basin-filling plains and basin exterior; moreover, several impact craters superposed on the interior plains exhibit dark haloes suggesting excavation of compositionally distinct material. Despite the generally poor surface resolution, possible endogenic features are recognized, including irregular rimless depressions. Mercurian volcanism may have occurred and in certain regions may resemble that of the Mare Australe region on the moon.

Comparison of Martian and lunar geologic provinces

Mars and the moon have superficially similar dichotomies between old elevated terrain and young low-lying terrain. On Mars the older terrain contains much less basin and crater material and much more plains material than the older terrain on the moon. These elevated Martian plains, constituting the plateau plains province, are believed to be depositional, perhaps volcanic, in origin. Some of the plateau plains are equivalent in crater density to a province of old lunar mare material in Mare Australe but are much more extensive. Like their lunar equivalents, these plateau plains are believed to have formed while the impact flux was declining from an early torrential rate to a later much slower rate. Other, younger Martian plains generally are also considerably more extensive relative to planet size than their lunar equivalents.

Lunar Maria and circular basins—a review

Lunar Orbiter data make it possible to examine the distribution and relations of maria and large circular basins over the entire Moon. The restricted distribution and age of the maria are in marked contrast to the apparently random distribution in time and place of the circular basins, some of which contain mare fillings. The circular basins are believed to be impact scars, and the maria to be volcanic fills which in each case are younger than the structures they fill. Twenty-nine circular basins 300 km wide or wider are recognized. They are placed in an age sequence because successive stages of degradation can be recognized from the fresh Orientale basin to the almost obliterated basin containing Mare Australe. The maria were emplaced during a short span of lunar history, although some light plains of the highlands may be older maria lightened through age. The present maria are topographically low, tend to be associated with large circular basins, and lie in a crude global belt of regional concentrations; 94% are on the hemisphere facing the Earth. Possible explanations offered for these patterns of mare distribution include impact-induced volcanism, volcanic extrusion to a hydrostatic level, isostatic compensation, lateral heterogeneity in the lunar interior, subcrustal convection, and volcanism due to disruption by Earth's gravity.