Lunar Reconnaissance Orbiter Camera Images Research Articles

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.

Giordano Bruno: Small crater populations––Implications for self-secondary cratering

Giordano Bruno is a lunar farside Copernican-age crater. The relatively few superposed impact craters on its floor and ejecta blanket and extensive bright rays indicate its youth. High-resolution Lunar Reconnaissance Orbiter Camera images reveal that the frequency and the characteristics of the cumulative size-frequency distributions of the small-diameter impact craters and their morphology vary across the clastic ejecta and impact melt covered surfaces. Crater frequencies (N(10) defined as ≥10 m km−2) vary by a factor of 10 s–100 s (N(10) 2–700) across the ejecta blanket, and between the ejecta and the melt deposits. Numerous craters on the ejecta blanket are degraded and buried by debris and impact melt, indicating that these partially buried craters formed during the deposition of the ejecta and prior to or during the emplacement of the impact melt. From geologic relations and crater statistics we conclude that a significant fraction of the craters observed on the ejecta blanket and the melt were formed during the cratering process itself and represent "self-secondaries." Further, we conclude that these craters do not represent an extra-lunar primary impact production population. Self-secondary craters are formed by material launched into near-vertical trajectories and having velocities such that their flight time is sufficiently long that the bulk of the clastic ejecta and impact melt are deposited before that material impacts the surface. The presence of a significant number of self-secondary craters on the ejecta makes the determination of relative and absolute age dates problematic. Crater counts would indicate an inappropriately old age. Using data for craters on the melt surfaces and for small-diameter bright ejecta craters, an absolute model age of 1 Ma is estimated. This age is considerably younger than that estimated by other studies and probably represents a maximum age.

Revisiting the field geology of Taurus–Littrow

Integration of Apollo 17 field observations and photographs, sample investigations, Lunar Reconnaissance Orbiter Camera images, Chandrayaan-1 Moon Mineralogy Mapper (M3) spectra, and Miniature Radio Frequency (Mini-RF) S-band radar images provides new insights into the geology of the valley of Taurus–Littrow on the Moon. Connecting the various remote observations to sample data enables a set of new conclusions to be drawn regarding the geological evolution of the valley. Structural considerations and published and recalculated 40Ar/39Ar analyses of samples from the North Massif and the Sculptured Hills indicate that the Crisium basin formed about 3.93 Ga; the Serenitatis basin about 3.82 Ga; and the Imbrium basin no earlier than 3.82 Ga and no later than the average of 3.72 Ga for 33 age dates from samples of the valley's mare basalts. Strong evidence continues to support the conclusion of others (Lucchitta, 1972; Spudis et al., 2011; Fassett et al., 2012) that the Sculptured Hills physiographic unit consists of Imbrium ejecta. Interpretation of M3 spectral data and Apollo 17 samples indicate that rock units of the Sculptured Hills consist of a largely coherent, Mg-suite pluton. LROC NAC stereo images and Mini-RF data indicate the presence of several exposed pyroclastic fissures across the Sculptured Hills. Rim boulders at Camelot Crater constitute nearly in situ wall rocks of that crater rather than ejecta and provide an opportunity for investigations of remanent magnetic field orientation at the time of the eruption of late mare basalt lavas in the valley. Paleomagnetic field orientation information also may be obtained relative to melt-breccia contacts in North Massif boulders that suggest original horizontal orientations. LROC images indicate the existence of two temporally separate light mantle avalanche deposits. The origin, potential flow mechanisms, and geology of the youngest avalanche from the South Massif have been clarified. The existence of two distinct light mantle avalanches raises doubt about the association of either light mantle avalanche with secondary impacts related to the Tycho impact event. Alternatively, the Lee-Lincoln thrust fault appears to have triggered the second light mantle avalanche between 70 and 110 Ma. A simple structural analysis shows that this thrust fault dips 20–25° to the southwest where it crosses the North Massif and to the west where it crosses the valley floor. Mini-RF data reveal a line of reduced reflections roughly perpendicular to contours on the North Massif about 3 km to the east of the Lee-Lincoln fault. Although this line is possibly an older ancillary fault, LROC NAC stereo images indicate that it may be best explained as a pyroclastic fissure. A debris flow of dark, apparent pyroclastic ash lies below the southeast end of the potential fissure. Finally, young lunar impact glass sample 70019 has been precisely located within LROC NAC images and oriented for the first time using 60 mm (f.l.) sample documentation photographs. Sample 70019 can now be employed in lunar paleomagnetic field orientation studies.

Cartography of the Luna-21 landing site and Lunokhod-2 traverse area based on Lunar Reconnaissance Orbiter Camera images and surface archive TV-panoramas

The Lunar Reconnaissance Orbiter Camera (LROC) system consists of a Wide Angle Camera (WAC) and Narrow Angle Camera (NAC). NAC images (∼0.5 to 1.7m/pixel) reveal details of the Luna-21 landing site and Lunokhod-2 traverse area. We derived a Digital Elevation Model (DEM) and an orthomosaic for the study region using photogrammetric stereo processing techniques with NAC images. The DEM and mosaic allowed us to analyze the topography and morphology of the landing site area and to map the Lunokhod-2 rover route. The total range of topographic elevation along the traverse was found to be less than 144m; and the rover encountered slopes of up to 20°. With the orthomosaic tied to the lunar reference frame, we derived coordinates of the Lunokhod-2 landing module and overnight stop points. We identified the exact rover route by following its tracks and determined its total length as 39.16km, more than was estimated during the mission (37km), which until recently was a distance record for planetary robotic rovers held for more than 40 years.

Complex explosive volcanic activity on the Moon within Oppenheimer crater

Oppenheimer crater is a floor-fractured crater located within the South Pole–Aitken basin on the Moon, and exhibits more than a dozen localized pyroclastic deposits associated with the fractures. Localized pyroclastic volcanism on the Moon is thought to form as a result of intermittently explosive Vulcanian eruptions under low effusion rates, in contrast to the higher-effusion rate, Hawaiian-style fire fountaining inferred to form larger regional deposits. We use Lunar Reconnaissance Orbiter Camera images and Diviner Radiometer mid-infrared data, Chandrayaan-1 orbiter Moon Mineralogy Mapper near-infrared spectra, and Clementine orbiter Ultraviolet/visible camera images to test the hypothesis that the pyroclastic deposits in Oppenheimer crater were emplaced via Vulcanian activity by constraining their composition and mineralogy. Mineralogically, we find that the deposits are variable mixtures of orthopyroxene and minor clinopyroxene sourced from the crater floor, juvenile clinopyroxene, and juvenile iron-rich glass, and that the mineralogy of the pyroclastics varies both across the Oppenheimer deposits as a whole and within individual deposits. We observe similar variability in the inferred iron content of pyroclastic glasses, and note in particular that the northwest deposit, associated with Oppenheimer U crater, contains the most iron-rich volcanic glass thus far identified on the Moon, which could be a useful future resource. We propose that this variability in mineralogy indicates variability in eruption style, and that it cannot be explained by a simple Vulcanian eruption. A Vulcanian eruption should cause significant country rock to be incorporated into the pyroclastic deposit; however, large areas within many of the deposits exhibit spectra consistent with high abundances of juvenile phases and very little floor material. Thus, we propose that at least the most recent portion of these deposits must have erupted via a Strombolian or more continuous fire fountaining eruption, and in some cases may have included an effusive component. These results suggest that localized lunar pyroclastic deposits may have a more complex origin and mode of emplacement than previously thought.

Global thrust faulting on the Moon and the influence of tidal stresses

Lunar Reconnaissance Orbiter Camera images reveal a vast, globally distributed network of over 3200 lobate thrust fault scarps, making them the most common tectonic landform on the Moon. Based on their small scale and crisp appearance, crosscutting relations with small-diameter impact craters, and rates of infilling of associated small, shallow graben, these fault scarps are estimated to be younger than 50 Ma and may be actively forming today. The non-random distribution of the scarp orientations is inconsistent with isotropic stresses from late-stage global contraction as the sole source of stress. We propose that tidal stresses contribute significantly to the current stress state of the lunar crust. Orbital recession stresses superimposed on stresses from global contraction with the addition of diurnal tidal stresses result in non-isotropic compressional stress and thrust faults consistent with lobate scarp orientations. The addition of diurnal tidal stresses at apogee result in peak stresses that may help trigger coseismic slip events on currently active thrust faults on the Moon.

New crater on the Moon and a swarm of secondaries

Lunar Reconnaissance Orbiter Camera images acquired both before and after the formation of an 18.8m diameter crater on 17 March 2013 reveal intricate details of ejecta distribution and the structure of the top two meters of the regolith. Our observations indicate that (1) the regolith is mature down to several tens of cm and immature below one meter, (2) surface reflectivity properties are affected for distances greater than fifty crater radii, and (3) large numbers of secondary impacts (splotches) formed up to 30km distant from this new primary crater. These observations provide new knowledge of the distribution of ejected materials from small impact craters on the Moon, the modification of the top few cm of the regolith by micrometeorite impacts, and potential hazards to future explorers.

Distribution, formation mechanisms, and significance of lunar pits

Lunar Reconnaissance Orbiter Camera images reveal the presence of steep-walled pits in mare basalt (n=8), impact melt deposits (n=221), and highland terrain (n=2). Pits represent evidence of subsurface voids of unknown extents. By analogy with terrestrial counterparts, the voids associated with mare pits may extend for hundreds of meters to kilometers in length, thereby providing extensive potential habitats and access to subsurface geology. Because of their small sizes relative to the local equilibrium crater diameters, the mare pits are likely to be post-flow features rather than volcanic skylights. The impact melt pits are indirect evidence both of extensive subsurface movement of impact melt and of exploitable sublunarean voids. Due to the small sizes of pits (mare, highland, and impact melt) and the absolute ages of their host materials, it is likely that most pits formed as secondary features.

The origin of Ina: Evidence for inflated lava flows on the Moon

Ina is an enigmatic volcanic feature on the Moon known for its irregularly shaped mounds, the origin of which has been debated since the Apollo Missions. Three main units are observed on the floor of the depression (2.9 km across, ≤64 m deep) located at the summit of a low‐shield volcano: irregularly shaped mounds up to 20 m tall, a lower unit 1 to 5 m in relief that surrounds the mounds, and blocky material. Analyses of Lunar Reconnaissance Orbiter Camera images and topography show that features in Ina are morphologically similar to terrestrial inflated lava flows. Comparison of these unusual lunar mounds and possible terrestrial analogs leads us to hypothesize that features in Ina were formed through lava flow inflation processes. While the source of the lava remains unclear, this new model suggests that as the mounds inflated, breakouts along their margins served as sources for surface flows that created the lower morphologic unit. Over time, mass wasting of both morphologic units has exposed fresh surfaces observed in the blocky unit. Ina is different than the terrestrial analogs presented in this study in that the lunar features formed within a depression, no vent sources are observed, and no cracks are observed on the mounds. However, lava flow inflation processes explain many of the morphologic relationships observed in Ina and are proposed to be analogous with inflated lava flows on Earth.

Persistently illuminated regions at the lunar poles: Ideal sites for future exploration

The Lunar Reconnaissance Orbiter Camera (LROC) provides multi-temporal and high resolution imaging of the north and south polar regions. These images delimit illuminated areas from those in shadow, and are used to analyze the illumination environment of the polar regions over the course of a lunar year. The Wide Angle Camera (WAC) provides repeat imaging of the north and south pole at a frequency of roughly 2h with a ground sampling distance of 100m. The LROC Narrow Angle Camera (NAC) acquires images with a ground sampling distance of 0.5–2.0m providing the means to construct high resolution maps that reveal illuminated terrain under varying lighting conditions. With the multi-temporal coverage provided by the WAC and the high resolution images from the NAC, the LROC dataset enables a more comprehensive analysis of the illumination conditions near the lunar poles than any previous image based dataset. Furthermore, these images are used to validate previously published numerical models that simulate polar illumination conditions. From our analysis of the LROC images, we identified localized regions where the lunar surface remains illuminated for nearly 94% of the year with the longest eclipsed period lasting only 43h. We also identified small illuminated peaks (tens of meters across) in areas previously modeled to be in shadow. Together, the WAC and NAC dataset provide direct, high resolution observations of the actual surface illumination environment of potential exploration sites near the lunar poles.

Characterisation of potential landing sites for the European Space Agency's Lunar Lander project

This article describes the characterisation activities of the landing sites currently envisaged for the Lunar Lander mission of the European Space Agency. These sites have been identified in the South Pole Region (−85° to−90° latitude) based on favourable illumination conditions, which make it possible to have a long-duration mission with conventional power and thermal control subsystems, capable of enduring relatively short periods of darkness (in the order of tens of hours), instead of utilising Radioisotope Heating Units. The illumination conditions are simulated at the potential landing sites based on topographic data from the Lunar Orbiter Laser Altimeter (LOLA), using three independent tools. Risk assessment of the identified sites is also being performed through independent studies. Long baseline slopes are assessed based on LOLA, while craters and boulders are detected both visually and using computer tools in Lunar Reconnaissance Orbiter Camera (LROC) images, down to a size of less than 2m, and size-frequency distributions are generated. Shadow hazards are also assessed via LROC images. The preliminary results show that areas with quasi-continuous illumination of several months exist, but their size is small (few hundred metres); the duration of the illumination period drops quickly to less than one month outside the areas, and some areas present gaps with short illumination periods. Concerning hazard distributions, 50m slopes are found to be shallow (few degrees) based on LOLA, whereas at the scale of the lander footprint (∼5m) they are mostly dominated by craters, expected to be mature (from geological context) and shallow (∼11°). The preliminary conclusion is that the environment at the prospective landing sites is within the capabilities of the Lander design.

Mapping the Apollo 17 landing site area based on Lunar Reconnaissance Orbiter Camera images and Apollo surface photography

Newly acquired high resolution Lunar Reconnaissance Orbiter Camera (LROC) images allow accurate determination of the coordinates of Apollo hardware, sampling stations, and photographic viewpoints. In particular, the positions from where the Apollo 17 astronauts recorded panoramic image series, at the so‐called “traverse stations”, were precisely determined for traverse path reconstruction. We analyzed observations made in Apollo surface photography as well as orthorectified orbital images (0.5 m/pixel) and Digital Terrain Models (DTMs) (1.5 m/pixel and 100 m/pixel) derived from LROC Narrow Angle Camera (NAC) and Wide Angle Camera (WAC) images. Key features captured in the Apollo panoramic sequences were identified in LROC NAC orthoimages. Angular directions of these features were measured in the panoramic images and fitted to the NAC orthoimage by applying least squares techniques. As a result, we obtained the surface panoramic camera positions to within 50 cm. At the same time, the camera orientations, North azimuth angles and distances to nearby features of interest were also determined. Here, initial results are shown for traverse station 1 (northwest of Steno Crater) as well as the Apollo Lunar Surface Experiment Package (ALSEP) area.

Soviet lunar sample return missions: Landing site identification and geologic context

The Lunar Reconnaissance Orbiter Camera (LROC) imaged the landing sites and spacecraft from the Soviet Union's Luna robotic sample return program (Luna 16, 20, and 24) allowing their locations to be determined with unprecedented precision and, more importantly, for the geologic context of the landing sites to be firmly established. Uncertainties in the position of the landing sites are now 25m (or better), as opposed to kilometers prior to LROC observations. Because of the past uncertainty of the locations, as well as the fact that two of the Luna missions were conducted at night, the geologic context of the samples was only poorly known. LROC images reveal that the Luna 24 sample was collected on the rim of a small impact crater, providing an explanation for the compositional and maturity discrepancy that has existed for the past three decades between samples and remote sensing of the Mare Crisium surface. The location of the unsuccessful Luna 23 spacecraft is also determined and the nature of the failure confirmed.

Recent extensional tectonics on the Moon revealed by the Lunar Reconnaissance Orbiter Camera

On the Moon, extensional tectonic features have only been observed close to the influence of the mare basalt-filled basins and floor-fractured craters. Analysis of Lunar Reconnaissance Orbiter Camera images reveals several potentially very young extensional tectonic features in the farside highlands, implying that extensional stresses may locally exceed compressional ones.

Non-mare silicic volcanism on the lunar farside at Compton–Belkovich

Non-basaltic volcanism is rare on the Moon and has been found predominantly on the lunar nearside. Analysis of Lunar Reconnaissance Orbiter Camera images and spectral data reveal the presence of compositionally evolved, non-basaltic volcanism on the lunar farside.

New insight into lunar impact melt mobility from the LRO camera

The Lunar Reconnaissance Orbiter Camera (LROC) is systematically imaging impact melt deposits in and around lunar craters at meter and sub‐meter scales. These images reveal that lunar impact melts, although morphologically similar to terrestrial lava flows of similar size, exhibit distinctive features (e.g., erosional channels). Although generated in a single rapid event, the post‐impact mobility and morphology of lunar impact melts is surprisingly complex. We present evidence for multi‐stage influx of impact melt into flow lobes and crater floor ponds. Our volume and cooling time estimates for the post‐emplacement melt movements noted in LROC images suggest that new flows can emerge from melt ponds an extended time period after the impact event.