Lunar Reconnaissance Orbiter Mission Research Articles

On the reachability and genesis of water ice on the Moon

Understanding the reachability of water ice by future in-situ experiments near the lunar poles is crucial for supporting growing exploration plans and constraining the uncertainties on its genesis and distribution. To achieve this objective, we perform a thorough three-dimensional mapping of the distribution of water ice in the lunar polar regions (70° onward), integrating radar, optical, and neutron detector observations from the Lunar Reconnaissance Orbiter mission (LRO). Our analysis reveals ∼5-to-8-fold larger expanse of subsurface water ice (∼1-3 m depth) compared to surface water ice (up to 1 m depth) for the north and south poles, respectively. Our investigation cannot rule out the possibility of deep-seated water ice deposits in the lunar poles that remains beyond the detection capabilities of existing instruments on LRO. Moreover, we find that the extent of water ice in the northern polar region (∼1100 ± 74 km2) is twice that in the southern polar region (∼562 ± 54 km2). Our mapping also suggests that the dichotomous latitudinal distribution and the antipodal longitudinal distribution of water ice are likely driven by Mare volcanism and preferential cratering. We provide additional evidence that outgassing during Imbrian volcanism was probably the primary source of subsurface water ice in the lunar poles, which favors larger expanse over meteoritic sources.

Automatic detection for small-scale lunar impact crater using deep learning

The impact crater is the most dominant geomorphic structural units over the planetary surface and its accurate extraction is of great significance to investigate the evolution of the Moon, the impact history of the solar system and the space environment. Through the impact crater’s identification, especially small-scale, and their spatial distribution characteristics, the impact flux, morphological characteristics, age of impact craters and surface degradation can be revealed. Therefore, this paper presents an automatic method for the impact crater detection, especially small-scale ones, using anchor-free deep learning. Due to the limitation of traditional object proposals for detecting different types of impact craters, we retrain the anchor-free CenterNet model using a transfer learning strategy, where the detection task of impact crater is formulated into the detection of its center point and regression of its property (i.e., size) without non-maximal suppression. We select the stacked Hourglass network as backbone to aggregate different levels of feature for enhancing the capability of estimating the impact crater centers. Moreover, we find the center points of impact craters on the image features’ heatmap only based on their locations, instead of box overlap, which allows us to detect different types of impact craters, even the impact craters that contain other impact craters. The model is trained in an end-to-end manner and applied to detect the impact craters on the lunar images between ±50° of latitude, with the spatial resolution of 100 m/pixel, from Wide Angle Camera (WAC) onboard Lunar Reconnaissance Orbiter (LRO) mission. The obtained results are compared relative to an existing crater database both qualitatively and quantitatively that suggests the reliability and robustness of the developed method in the automatic detection of small-scale impact craters, where the smallest one is 500 m. Moreover, the developed method is capable to detect different types of impact craters, including dispersal and connective ones, with the recall of 73.66% and precision of 78.27% compared with an existing crater database. The code is publicly available at https://github.com/ShuoweiZhang/crater_detection.

Geology of the Crüger-Sirsalis Basin: Evidence for prolonged volcanism in the southwestern near side of the Moon

The Pre-Nectarian Crüger-Sirsalis Basin (centered at 16.0°S, 293.0°E; ~ 475 km in diameter) is a primarily degraded and obscured impact basin on the Moon. This study presents the first geological description of the Crüger-Sirsalis Basin using remote sensing datasets from Lunar Reconnaissance Orbiter (LRO), Chandrayaan-1, and Kaguya missions. An inner depression ring (IDR) with a diameter of ~243 km has been identified, besides two of its outer rings with diameters of ~425 km and ~ 475 km. We report two new floor fractured craters, and a new concentric crater, suggesting the presence of shallow magmatic intrusions. A new pyroclastic deposit has been found within the Crüger-Sirsalis Basin. Our spectral assessment of the cryptomaria and mare basalt reveals two different types of cryptomaria in the region. The cryptomare inside the basin possesses similar olivine-pyroxene composition as basalt within the basin. However, the cryptomare outside the Crüger-Sirsalis Basin, towards the Oceanus Procellarum, is predominantly composed of high-Ca pyroxene. The spectral signature of pure anorthosite (PAN) has been found in crater Darwin C, located along the inner ring of the basin. The Byrgius Crater along the outer ring of the basin shows the spectral signature of olivine or Fe-rich glass mixed with orthopyroxene. Crater chronology has revealed that the basin experienced main phase and late phase volcanism, down to ~1.4 Ga. Thus, the Crüger-Sirsalis Basin uniquely experienced prolonged mare volcanism from the pre-cataclysmic stage to the late stage of lunar history.

Long‐Term Observations of Galactic Cosmic Ray LET Spectra in Lunar Orbit by LRO/CRaTER

AbstractThe Cosmic Ray Telescope for the Effects of Radiation (CRaTER) has been orbiting the Moon since 2009 aboard the Lunar Reconnaissance Orbiter (LRO). From this vantage point, it samples the interplanetary energetic particle population outside the shielding of the Earth's magnetosphere. We report the sensor's observations of galactic cosmic rays (GCRs) over a complete solar activity cycle. CRaTER is designed primarily to measure not the spectra of GCR particles outside the sensor but rather their effects on matter, and in particular, it measures the linear energy transfer (LET) or energy‐deposit spectrum in its silicon detectors. We have used the Geant4 radiation‐transport code to devise a background‐rejection algorithm to improve these measurements of LET under 9.9 g/cm2 of shielding, and the resulting observations show the changing radiation effects of GCRs as their intensity and spectrum vary with solar modulation. As of 2020 this intensity, after declining during solar maximum activity, has recovered to a level that exceeds by a few percent the historically high values seen during the deep solar minimum at the start of the LRO mission in 2009.

A Deep Learning Approach to Hazard Detection for Autonomous Lunar Landing

A deep learning approach is presented to detect safe landing locations using LIDAR scans of the Lunar surface. Semantic Segmentation is used to classify hazardous and safe locations from a LIDAR scan during the landing phase. Digital Elevation Maps from the Lunar Reconnaissance Orbiter mission are used to generate the training, validation, and testing dataset. The ground truth is generated using geometric techniques by evaluating the surface roughness, slope, and other hazard avoidance specifications. In order to train a robust model, artificially generated training data is augmented to the training dataset. A UNet-like neural network structure learns a lower dimensional representation of LIDAR scan to retain essential information regarding safety of the landing locations. A softmax activation layer at the bottom of the network ensures that the network outputs a probability of a safe landing spot. The network is also trained with a cost function that prioritizes the false safes to achieve a sub 1% false safes value. The results presented show the effectiveness of the technique for hazard detection. Future work on electing one landing spot based on proximity to the intended landing spot and the size of safety region around it is motivated.

Lunar Titanium and Frequency‐Dependent Microwave Loss Tangent as Constrained by the Chang'E‐2 MRM and LRO Diviner Lunar Radiometers

AbstractPassive microwave frequency (~300 MHz to 300 GHz) observations of the Moon have a long history and have been suggested as a plausible orbital instrument for the Moon and other bodies. However, global, orbital multifrequency measurements of lunar passive microwave emission have only recently been made by the Chinese Chang'E‐1 and ‐2 microwave radiometer (MRM) instruments. These missions carried nearly identical 4‐channel (3.0, 7.8, 19.35, and 37 GHz) instruments into lunar orbit in 2007–2009 and 2010–2011, respectively. Over the same time period, the ongoing Lunar Reconnaissance Orbiter (LRO) mission carried the Diviner Lunar Radiometer, which collected surface temperature measurements in the far infrared (~7.8–400 μm) from 2009 to present. By combining these data and associated thermal models, we provide new constraints on the relationship between physical temperature and microwave brightness temperature to reveal novel information about regolith thermal and dielectric properties which can reveal unique geologic information about the Moon. Here, we describe several first‐order global results to come from this combined data set, focusing primarily on the ability to detect, map, and quantify dielectric loss tangent variations of the Moon, including those from the presence of titanium‐bearing ilmenite. We update the loss tangent models for both highlands and mare and identify a clear frequency dependence that differs in sign between the two. We use the correlation with visible wavelength TiO2 mapping to provide a means to separate out the loss from rocks and from that of composition.

Mini-RF S-band observation of Ohm and Stevinus craters using circular polarization ratio and m-chi decomposition techniques

The aim of the study was to observe two lunar impact craters of Copernican age, Ohm (18.4°N, 113.5°W) and Stevinus (32.5°S, 54.2°E) under microwave radar data of Miniature Radio Frequency (Mini-RF), an instrument onboard Lunar Reconnaissance Orbiter (LRO) of NASA, where Ohm is located on the far side of the Moon and Stevinus is situated on the near side of the Moon. We have analyzed the characters of impact ejecta melt of both the craters in radar data which are not evidently distinguished in the high resolution optical data of narrow angle camera (NAC) and wide angle camera (WAC) of LRO mission. Circular polarization ratio (CPR) and m-chi decomposition images were developed using ENVI and ArcGIS software which were used to understand surface roughness and backscattering properties of Ohm and Stevinus craters. Both the craters evidently have high CPR values indicating either exposure of fresh material or elevated surface roughness due to surface geometry. The m-chi decomposition of Ohm and Stevinus craters shows dominant yellowish hue suggesting a backscatter combination of double-bounce (db) scattering and volume scattering (vs) in contrast to the surrounding terrain which shows Bragg scattering (bs) according to the 7-fold classification colour-wheel. Using available optical and Mini-RF data geological maps of both the craters were generated including features such as boundary of ejecta blanket, ejecta boulders and mass wasting in the crater.

In-flight characterization of the lunar orbiter laser altimeter instrument pointing and far-field pattern.

The Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO) has collected nearly seven billion measurements of surface height on the Moon with an absolute accuracy of ∼1 m and a precision of ∼10 cm. Converting time-of-flight laser altimeter measurements to topographic elevations requires accurate knowledge of the laser pointing with respect to the spacecraft body-fixed coordinate system. To that end, we have utilized altimetric crossovers from LOLA, as well as bidirectional observations of the LOLA laser and receiver boresight via an Earth-based laser tracking ground station. Based on a sample of ∼780,000 globally distributed crossovers from the circular-orbit phase of LRO's mission (∼27 months), we derive corrections to the LOLA laser boresight. These corrections improve the cross-track and along-track agreement of the crossovers by 24% and 33%, respectively, yielding RMS residuals of ∼10 m. Since early in the LRO mission, the bidirectional laser tracking experiments have confirmed a pointing anomaly when the LOLA instrument is facing toward deep space or the night side of the Moon and have allowed the reconstruction of the laser far-field pattern and receiver telescope pointing. By conducting such experiments shortly after launch and nearly eightyears later, we have directly measured changes in the laser characteristics and obtained critical data to understand the laser behavior and refine the instrument pointing model. The methods and results presented here are also relevant to the design, fabrication, and operation of future planetary laser altimeters and their long-term behavior in the space environment.

Problem of lunar mascons: An alternative approach

The origin of lunar mascons is discussed on the base of results of the orbital experimental exploration of the Moon by the Gravity Recovery and Interior Laboratory and the Lunar Reconnaissance Orbiter missions. We lead the discussion on the basis of representations of Galactocentric paradigm which links processes in the Solar System and on its planets with the Galaxy influences. The article describes a new approach to the interpretation of the crater data, which takes into account the quasi-periodic bombardments of the Moon by galactic comets. We present a preliminary evaluation of the age of mascons as well as of craters and mares on the Moon based on this approach.

Reaction: Chemistry Driven by the Harsh Space Environment

Dr. Bill Farrell is a plasma physicist at NASA's Goddard Space Flight Center. He is a co-investigator on the Cassini mission to Saturn and the Parker Solar Probe mission. He is also principal investigator of the DREAM2 Center for Space Environments (http://ssed.gsfc.nasa.gov/dream/), which examines the exosphere formation, radiation effects, and plasma interactions of the Moon and other airless bodies. Dr. Farrell has authored or co-authored over 200 journal articles on various aspects of space science, including the hydroxylation at the Moon, the curious plasma effects within the Enceladus plume, and the possibility of electricity generated in Martian dust devils.

Characterizing dark mantle deposits in the lunar crater Alphonsus

We analyze available remote-sensing data of the crater Alphonsus, focusing on the analysis of the crater's dark mantle deposits (DMDs), which includes images from NASA Clementine and Lunar Reconnaissance Orbiter (LRO), Japanese Selene (Kaguya), and Indian Chandrayaan-1 missions. The Alphonsus DMDs are gentle-sloped flat hills with typical heights of several meters, which are presented with pyroclastic materials. Our determination of the absolute ages of the Alphonsus DMDs by the technique of crater size-frequency distributions shows that they are ∼200–400 m.y. old. However, being geologically young, the Alphonsus DMDs are not seen in OMAT maps. The DMDs have noticeably lower content of TiO2 (2–3%) than the mare regions to the west (>4%). The assessment of total pyroxene shows it has a higher abundance in the DMDs, although LRO Diviner measurements of the Chirstiansen feature suggest, rather, a high abundance of olivine. The DMDs pyroclastic material has no signs of OH/H2O compounds. We may suggest that this characteristic of the DMDs either relates to their impact reworking and loss of the OH/H2O compounds or to the non-water volatiles as the driving agent of the pyroclastic activity. The compositional assessments of the DMDs may be flawed from contamination with the surrounding material due to horizontal and vertical transportation due to impacts. This effect probably can be observed in LROC NAC images of high resolution. A very dark material outcropping on the slopes of the vent depression is seen due to renovation of the regolith on the steep walls of the depression. Thus, at smaller phase angles, the pyroclastic material is dark and at larger phase angles it appears almost like the surrounding material. This means that the phase dependence of the outcropping dark material is shallow; i.e. the dark surface is smoother than its surroundings. This may suggest venting of gases resulting in fluidization of the granular pyroclastic material of the deposit.

Investigation of newly discovered lobate scarps: Implications for the tectonic and thermal evolution of the Moon

Using observations of lunar scarps in Apollo Panoramic Camera photos, Binder and Gunga (1985) tested competing models for the initial thermal state of the Moon, i.e., whether it was initially completely molten or if the molten portion was limited to a global magma ocean. Binder and Gunga (1985) favored the concept of an initially molten Moon that had entered into a late-stage epoch of global tectonism. Since the start of the Lunar Reconnaissance Orbiter mission, thousands of new small lobate scarps have been identified across the lunar surface with high-resolution images from the Lunar Reconnaissance Orbiter Camera (LROC). As such, we selected spatially random scarps and reevaluated the fault dynamical calculations presented by Binder and Gunga (1985). Additionally, we examined the geometry and properties of these fault scarps and place better constraints on the amount of scarp-related crustal shortening. We found that these low angle thrust faults (∼23˚) have an average relief of ∼40 m and average depths of 951 m. Using crater size-frequency distribution (CSFD) measurements, we derived absolute model ages for the scarp surfaces proximal to the trace of the fault and found that the last slip event occurred in the last ∼132 Ma. Along with young model ages, lunar lobate scarps exhibit a youthful appearance with their crisp morphologies which is indicative of late-stage horizontal shortening. In conclusion, interior secular cooling and tidal stresses cause global contraction of the Moon.

The rate of dielectric breakdown weathering of lunar regolith in permanently shadowed regions

Large solar energetic particle events may cause dielectric breakdown in the upper 1 mm of regolith in permanently shadowed regions (PSRs). We estimate how the resulting breakdown weathering compares to meteoroid impact weathering. Although the SEP event rates measured by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO) are too low for breakdown to have significantly affected the regolith over the duration of the LRO mission, regolith gardened by meteoroid impacts has been exposed to SEPs for ∼106 yr. Therefore, we estimate that breakdown weathering’s production rate of vapor and melt in the coldest PSRs is up to 1.8−3.5×10−7 kg m−2 yr−1, which is comparable to that produced by meteoroid impacts. Thus, in PSRs, up to 10–25% of the regolith may have been melted or vaporized by dielectric breakdown. Breakdown weathering could also be consistent with observations of the increased porosity (“fairy castles”) of PSR regolith. We also show that it is conceivable that breakdown-weathered material is present in Apollo soil samples. Consequently, breakdown weathering could be an important process within PSRs, and it warrants further investigation.

Summary of the results from the lunar orbiter laser altimeter after seven years in lunar orbit

In June 2009 the Lunar Reconnaissance Orbiter (LRO) spacecraft was launched to the Moon. The payload consists of 7 science instruments selected to characterize sites for future robotic and human missions. Among them, the Lunar Orbiter Laser Altimeter (LOLA) was designed to obtain altimetry, surface roughness, and reflectance measurements. The primary phase of lunar exploration lasted one year, following a 3-month commissioning phase. On completion of its exploration objectives, the LRO mission transitioned to a science mission. After 7 years in lunar orbit, the LOLA instrument continues to map the lunar surface. The LOLA dataset is one of the foundational datasets acquired by the various LRO instruments. LOLA provided a high-accuracy global geodetic reference frame to which past, present and future lunar observations can be referenced. It also obtained high-resolution and accurate global topography that were used to determine regions in permanent shadow at the lunar poles. LOLA further contributed to the study of polar volatiles through its unique measurement of surface brightness at zero phase, which revealed anomalies in several polar craters that may indicate the presence of water ice. In this paper, we describe the many LOLA accomplishments to date and its contribution to lunar and planetary science.

GEOMETRIC CALIBRATION OF THE CLEMENTINE UVVIS CAMERA USING IMAGES ACQUIRED BY THE LUNAR RECONNAISSANCE ORBITER

Abstract. The Clementine UVVIS camera returned over half a million images while in orbit around the Moon in 1994. Since the Clementine mission, our knowledge of lunar topography, gravity, and the location of features on the surface has vastly improved with the success of the Gravity Recovery and Interior Laboratory (GRAIL) mission and ongoing Lunar Reconnaissance Orbiter (LRO) mission. In particular, the Lunar Reconnaissance Orbiter Camera (LROC) has returned over a million images of the Moon since entering orbit in 2009. With the aid of improved ephemeris and on-orbit calibration, the LROC team created a series of precise and accurate global maps. With the updated reference frame, older lunar maps, such as those generated from Clementine UVVIS images, are misaligned making cross-mission analysis difficult. In this study, we use feature-based matching routines to refine and recalibrate the interior and exterior orientation parameters of the Clementine UVVIS camera. After applying these updates and rigorous orthorectification, we are able generate precise and accurate maps from UVVIS images to help support lunar science and future cross-mission investigations.

GEOMETRIC CALIBRATION OF THE CLEMENTINE UVVIS CAMERA USING IMAGES ACQUIRED BY THE LUNAR RECONNAISSANCE ORBITER

The Clementine UVVIS camera returned over half a million images while in orbit around the Moon in 1994. Since the Clementine mission, our knowledge of lunar topography, gravity, and the location of features on the surface has vastly improved with the success of the Gravity Recovery and Interior Laboratory (GRAIL) mission and ongoing Lunar Reconnaissance Orbiter (LRO) mission. In particular, the Lunar Reconnaissance Orbiter Camera (LROC) has returned over a million images of the Moon since entering orbit in 2009. With the aid of improved ephemeris and on-orbit calibration, the LROC team created a series of precise and accurate global maps. With the updated reference frame, older lunar maps, such as those generated from Clementine UVVIS images, are misaligned making cross-mission analysis difficult. In this study, we use feature-based matching routines to refine and recalibrate the interior and exterior orientation parameters of the Clementine UVVIS camera. After applying these updates and rigorous orthorectification, we are able generate precise and accurate maps from UVVIS images to help support lunar science and future cross-mission investigations.

Coordinates of anthropogenic features on the Moon

High-resolution images from the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) reveal the landing locations of recent and historic spacecraft and associated impact sites across the lunar surface. Using multiple images of each site acquired between 2009 and 2015, an improved Lunar Reconnaissance Orbiter (LRO) ephemeris, and a temperature-dependent camera orientation model, we derived accurate coordinates (<12m) for each soft-landed spacecraft, rover, deployed scientific payload, and spacecraft impact crater that we have identified. Accurate coordinates enhance the scientific interpretations of data returned by the surface instruments and of returned samples of the Apollo and Luna sites. In addition, knowledge of the sizes and positions of craters formed as the result of impacting spacecraft provides key benchmarks into the relationship between energy and crater size, as well as calibration points for reanalyzing seismic measurements acquired during the Apollo program. We identified the impact craters for the three spacecraft that impacted the surface during the LRO mission by comparing before and after NAC images.

Geological mapping of impact melt deposits at lunar complex craters Jackson and Tycho: Morphologic and topographic diversity and relation to the cratering process

High resolution geological mapping, aided by imagery and elevation data from the lunar reconnaissance orbiter (LRO) and Kaguya missions, has revealed the scientifically rich character of impact melt deposits at two young complex craters: Jackson (71km) and Tycho (85km). The morphology and distribution of mapped impact melt units provide several insights into the cratering process. We report elevation differences (>200m) among large, coherent floor sections within a single crater and interpret them to be caused by crater wall collapse and/or large scale structural failure of the floor region. Clast-poor, smooth melt deposits are correlated with floor sections at lower elevations and likely represent ponded deposits sourced from higher elevation regions (viz. crater walls). In addition, these deposits are also located in the inferred downrange direction of the impact. Melt-coated large blocks spanning several kilometers are common on the crater floors and may represent collapsed wall sections or in some cases, subdued sections of the central peaks. Spatial trends in the mapped impact melt units at the two craters provide clues to decipher the conditions during each impact event and subsequent evolution of the crater floor.

Optimized traverse planning for future polar prospectors based on lunar topography

To fully understand the extensive collection of remotely sensed polar observations by the Lunar Reconnaissance Orbiter and other recent lunar missions, we must acquire an array of ground-truth measurements. A polar rover can sample and assay potential polar resources both laterally and at shallow depths. To identify ideal, least-energy traverses for such a polar prospecting mission, we developed a traverse planning tool, called R-Traverse, using a fundamental wheel–regolith interaction model and datasets from the Lunar Reconnaissance Orbiter Camera, Lunar Orbiter Laser Altimeter, and Diviner Lunar Radiometer Experiment. Using the terramechanics model, we identified least-energy traverses at the 20 m scale around Shackleton crater and located one traverse plan that enables the rover to remain illuminated for 94.4% of the lunar year. By incorporating this path planning tool during mission planning, the feasibility of such a mission can be quantified.

Estimation of lunar FeO abundance based on imaging by LRO Diviner

Understanding the abundance and distribution characteristics of FeO on the surface of the Moon is important for investigating its evolution. The current high resolution maps of the global FeO abundance are mostly produced with visible and near infrared reflectance spectra. The Christiansen Feature (CF) in mid-infrared has strong sensitivity to lunar minerals and correlates to major elements composing minerals. This paper investigates the possibility of mapping global FeO abundance using the CF values from the Diviner Lunar Radiometer Experiment aboard the Lunar Reconnaissance Orbiter (LRO) mission. A high correlation between the CF values and FeO abundances from the Apollo samples was found. Based on this high correlation, a new global map (±60°) of FeO was produced using the CF map. The results show that the global FeO average is 8.2 wt.%, the highland average is 4.7 wt.%, the global modal abundance is 5.4 wt.% and the lunar mare mode is 15.7 wt.%. These results are close to those derived from data provided by Clementine, the Lunar Prospector Gamma Ray Spectrometer (LP-GRS) and the Chang'e-1 Interference Imaging Spectrometer (IIM), demonstrating the feasibility of estimating FeO abundance based on the Diviner CF data. The near global FeO abundance map shows an enrichment of lunar major elements.