Lunar Crater Observation Research Articles

Topography‐Enhanced Ultra‐Cold Trapping at the LCROSS Impact Site

AbstractSmall topographic features below the resolution of existing orbital data sets may create “micro ultra‐cold traps” within the larger permanently shadowed regions that are present at the lunar poles. These ultra‐cold traps are protected from the major primary and secondary illumination sources, and thus would create surfaces that are much colder than lower‐resolution temperature maps would indicate. We examine this effect by creating a high resolution (1 m pix−1) terrain map based on upscaled data from the Lunar Orbiter Laser Altimeter. This map is illuminated by scattered sunlight and infrared emissions from sunlit terrain, which are then run through a thermal model to determine temperatures. We find that while most of the terrain experiences maximum temperatures around 50 K, there are a number of 1–30 m‐scale ultra‐cold traps with maximum temperatures as low as 20–30 K. By comparing our modeled ultra‐cold trapping area to volatile abundances measured by Lunar Crater Observation and Sensing Satellite (LCROSS), we reveal a diverse environment where the surficial abundances necessary to explain the LCROSS results are strongly dependent on precisely where the impact occurred.

Analysis of the permanently shadowed region of Cabeus crater in lunar south pole using orbiter high resolution camera imagery

The Orbiter High Resolution Camera (OHRC) on-board India's Chandrayaan-2 orbiter mission had acquired two images of the Permanently Shadowed Region (PSR) and adjacent area of Cabeus crater at an unprecedented resolution (<0.3 m/pixel). Numerous small features, such as meter scale boulders, craters, and slope-normal lobes were identified in these images. Boulders and craters as small as 1.5 m and 1.8 m, respectively, were identified in PSR making this size limit two times better than the currently reported values (>3 m for boulders and > 4 m for craters). The crater size distributions in PSR and Non-PSR regions were found to be alike in the size range of 3–20 m. We identified over 20% more smaller craters (<3 m) in the Non-PSR areas as compared to the PSR because of the higher illumination in the Non-PSR. Slope-normal lobes (potentially related to the presence of ice) were present in PSR as well as in Non-PSR areas. The impact generated debris (potentially) of Lunar Crater Observation and Sensing Satellite (LCROSS) impactors were also identified inside the Cabeus crater. Finally, it is concluded that OHRC is one of the most suitable camera, presently available on any orbiter around the Moon, for the imaging of PSRs to facilitate the study of small surface features that might be related to surface/subsurface ice, and equally important for the trafficability inside the PSRs.

Time Series Analysis Methods and Detectability Factors for Ground-Based Imaging of the LCROSS Impact Plume

On 9 October 2009, multiple telescopes were used in a coordinated international observing campaign to acquire ground-based time series imaging to monitor the evolution of the impact plume from NASA’s Lunar CRater Observation and Sensing Satellite (LCROSS) mission. Although standard image processing techniques applied to these data were unsuccessful at detecting the presence of any impact plume, one detection was reported after processing images with Principal Component Analysis (PCA) filtering. In this work, we develop improvements to PCA filtering that increase the signal-to-noise ratio (SNR) of plume lightcurves. We use this updated methodology to remove atmospheric seeing effects not accounted for in the previous work, such as geometric distortions. We assess the robustness of PCA filtering as we search for plume detections in observations from five additional cameras in comparison with each pixel’s lightcurve during the final 40 s prior to impact to match the approximate duration of post-impact excess brightness. We explore the resulting combination of three detections and three non-detections to determine criteria for detectability in future observations of low SNR transient events. Our results indicate three observational setup constraints for optimizing the success of PCA filtering: (1) full-frame scattered light should not exceed the dynamic range between the illuminated and unilluminated surfaces, (2) the camera’s analog-to-digital conversion (ADC) should use at least 16-bit resolution, and (3) the ADC should not use gamma correction. We find that poor spatial or temporal resolution do not significantly degrade detectability, which suggests that any future LCROSS-like events may be detectable in PCA-filtered amateur observations.

Exogenic origin for the volatiles sampled by the Lunar CRater Observation and Sensing Satellite impact

Returning humans to the Moon presents an unprecedented opportunity to determine the origin of volatiles stored in the permanently shaded regions (PSRs), which trace the history of lunar volcanic activity, solar wind surface chemistry, and volatile delivery to the Earth and Moon through impacts of comets, asteroids, and micrometeoroids. So far, the source of the volatiles sampled by the Lunar Crater Observation and Sensing Satellite (LCROSS) plume has remained undetermined. We show here that the source could not be volcanic outgassing and the composition is best explained by cometary impacts. Ruling out a volcanic source means that volatiles in the top 1-3 meters of the Cabeus PSR regolith may be younger than the latest volcanic outgassing event (~1 billion years ago; Gya).

Alternative Propellant Nuclear Thermal Propulsion Engine Architectures

Recently, NASA’s Artemis Program has considered sustainably returning humans to the moon with in situ resource utilization as the central focus and considers nuclear thermal propulsion (NTP) to be a viable propulsion system candidate for deep space missions. This program also considers the moon to function as a staging area for deep space missions due to its strategic orbit around Earth. The Lunar Crater Observation and Sensing Satellite discovered the abundancy of water, ammonia, and other volatiles in permanently shadowed regions on the moon. Because NTP can theoretically use any fluid as a propellant, water and ammonia are two potential alternative propellants to hydrogen that do not require postprocessing to be used directly in situ. Alternative propellant NTP engine models were developed to examine the performance of water and ammonia. It was found that bleed cycle architectures are infeasible with current turbine materials, but expander cycles have acceptable turbine inlet temperatures with marginal performance differences from bleed cycles. At reactor power levels comparable to hydrogen NTP engines, water doubles the thrust while ammonia increases it by 70%, although at a much lower specific impulse. The largest contributor to the life of the engine was the maximum temperature of the SiC cladding for water and the maximum temperature of the fuel for ammonia where higher values resulted in shorter engine life.

Water within a permanently shadowed lunar crater: Further LCROSS modeling and analysis

The 2009 Lunar CRater Observation and Sensing Satellite (LCROSS) impact mission detected water ice absorption using spectroscopic observations of the impact-generated debris plume taken by the Shepherding Spacecraft, confirming an existing hypothesis regarding the existence of water ice in permanently shadowed regions within Cabeus crater. Ground-based observations in support of the mission were able to further constrain the mass of the debris plume and the concentration of the water ice ejected during the impact. In this work, we explore additional constraints on the initial conditions of the pre-impact lunar sediment required in order to produce a plume model that is consistent with the ground-based observations. We match the observed debris plume lightcurve using a layer of dirty ice with an ice concentration that increases with depth, a layer of pure regolith, and a layer of material at about 6 m below the lunar surface that would otherwise have been visible in the plume but has a high enough tensile strength to resist excavation. Among a few possible materials, a mixture of regolith and ice with a sufficiently high ice concentration could plausibly produce such a behavior. The vertical albedo profiles used in the best fit model allows us to calculate a pre-impact mass of water ice within Cabeus crater of 5±3.0×1011 kg and a mass concentration of water in the lunar sediment of 8.2±0.001 %wt, assuming a water ice albedo of 0.8 and a lunar regolith density of 1.5 g cm−3, or a mass concentration of water of 4.3±0.01 %wt, assuming a lunar regolith density of 3.0. These models fit to ground-based observations result in derived masses of regolith and water ice within the debris plume that are consistent with in situ measurements, with a model debris plume ice mass of 108 kg.

Characterizing the hydroxyl observation of the LCROSS UV-visible spectrometer: Modeling of the impact plume

Lunar Crater Observation and Sensing Satellite (LCROSS) impacted the Cabeus crater near the lunar South Pole on 9 October 2009 and generated an impact plume. The hydroxyl (OH) band strength observations obtained from the LCROSS mission are explained with the help of numerical modeling of the impact plume. We provide different models of OH production in the plume and conduct a parametric study to constrain the independent parameters of these models. In particular, detailed lofted grain heating, sublimation and photodissociation models are implemented along with models for H2O and OH production from the residual impact crater. Results show that the likely sources of observed OH are from a small amount of direct/abrasional OH desorption from regolith grains (~28 g) in the crater and from sublimation of water vapor (O(800 kg)) from lofted regolith-imbued ice grains followed by photodissociation.

Luna-5 (1965): Some Results of a Failed Mission to the Moon

Luna-5 was the second Soviet spacecraft to reach the Moon. During the first decade of space exploration of the Moon, the Luna probe series was the main part of the Soviet scientific program. The tasks of the Luna-5 probe launched to the Moon in May 1965 were to land softly on the lunar surface, take photos, and study the surface. Before the Luna-5 landing, the prospective coordinates of the landing site were telegraphed to observatories so that they would observe the event. However, during its descent, the braking engine failed and the probe crash landed at 22 h 13 min on May 12, 1965. Later, new supposed coordinates of the impact were reported. All the experiments were undoubtedly lost; nevertheless, successive television images of the failed landing made at the Abastumani Astrophysical Observatory (AbAO) of the Georgian Academy of Sciences can be considered a specific scientific result of the mission. In the images, a changeable object was detected near the large Lansberg crater; for obscure secrecy reasons, almost nothing was reported to specialists about this object. It has been identified as a small, gradually spreading impact cloud. An analysis of the reprocessed images taken at the AbAO has revealed the exact coordinates of the Luna-5 impact for the first time to be 1.35° S, 25.48° W, which differ substantially the calculation data published earlier. Some properties of the regolith at the Luna-5 impact site are compared to the results of the Lunar Crater Observation and Sensing Satellite (LCROSS) related to the region near the south pole of the Moon and reported in 2010.

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.

Partitioning a Large Simulation as It Runs

As computer simulations continue to grow in size and complexity, they present a particularly challenging class of big data problems. Many application areas are moving toward exascale computing systems, systems that perform 1018 FLOPS (FLoating-point Operations Per Second)—a billion billion calculations per second. Simulations at this scale can generate output that exceeds both the storage capacity and the bandwidth available for transfer to storage, making post-processing and analysis challenging. One approach is to embed some analyses in the simulation while the simulation is running—a strategy often called in situ analysis—to reduce the need for transfer to storage. Another strategy is to save only a reduced set of time steps rather than the full simulation. Typically the selected time steps are evenly spaced, where the spacing can be defined by the budget for storage and transfer. This article combines these two ideas to introduce an online in situ method for identifying a reduced set of time steps of the simulation to save. Our approach significantly reduces the data transfer and storage requirements, and it provides improved fidelity to the simulation to facilitate post-processing and reconstruction. We illustrate the method using a computer simulation that supported NASA's 2009 Lunar Crater Observation and Sensing Satellite mission.

Evolution of the dust and water ice plume components as observed by the LCROSS visible camera and UV–visible spectrometer

The LCROSS (Lunar Crater Observation and Sensing Satellite) impacted the Cabeus crater near the lunar South Pole on 9 October 2009 and created an impact plume that was observed by the LCROSS Shepherding Spacecraft. Here we analyze data from the ultraviolet–visible spectrometer and visible context camera aboard the spacecraft. We use these data to constrain a numerical model to understand the physical evolution of the resultant plume. The UV–visible light curve peaks in brightness 18s after impact and then decreases in radiance but never returns to the pre-impact radiance value for the ∼4min of observation by the Shepherding Spacecraft. The blue:red spectral ratio increases in the first 10s, decreases over the following 50s, remains constant for approximately 150s, and then begins to increase again ∼180s after impact. Constraining the modeling results with spacecraft observations, we conclude that lofted dust grains remained suspended above the lunar surface for the entire 250s of observation after impact. The impact plume was composed of both a high angle spike and low angle plume component. Numerical modeling is used to evaluate the relative effects of various plume parameters to further constrain the plume properties when compared with the observational data. Dust particle sizes lofted above the lunar surface were micron to sub-micron in size. Water ice particles were also contained within the ejecta cloud and simultaneously photo-dissociated and sublimated after reaching sunlight.

DETECTION OF OCEAN GLINT AND OZONE ABSORPTION USINGLCROSSEARTH OBSERVATIONS

The Lunar CRater Observation and Sensing Satellite (LCROSS) observed the distant Earth on three occasions in 2009. These data span a range of phase angles, including a rare crescent phase view. For each epoch, the satellite acquired near-infrared and mid-infrared full-disk images, and partial-disk spectra at 0.26-0.65 microns (R~500) and 1.17-2.48 microns (R~50). Spectra show strong absorption features due to water vapor and ozone, which is a biosignature gas. We perform a significant recalibration of the UV-visible spectra and provide the first comparison of high-resolution visible Earth spectra to the NASA Astrobiology Institute's Virtual Planetary Laboratory three-dimensional spectral Earth model. We find good agreement with the observations, reproducing the absolute brightness and dynamic range at all wavelengths for all observation epochs, thus validating the model to within the ~10% data calibration uncertainty. Data-model comparisons reveal a strong ocean glint signature in the crescent phase dataset, which is well matched by our model predictions throughout the observed wavelength range. This provides the first observational test of a technique that could be used to determine exoplanet habitability from disk-integrated observations at visible and near-infrared wavelengths, where the glint signal is strongest. We examine the detection of the ozone 255 nm Hartley and 400-700 nm Chappuis bands. While the Hartley band is the strongest ozone feature in Earth's spectrum, false positives for its detection could exist. Finally, we discuss the implications of these findings for future exoplanet characterization missions.

Characterization of the LCROSS impact plume from a ground-based imaging detection

The Lunar CRater Observation and Sensing Satellite (LCROSS) mission was designed to search for evidence of water in a permanently shadowed region near the lunar south pole. An instrumented Shepherding Spacecraft followed a kinetic impactor and provided--from a nadir perspective--the only images of the debris plume. With independent observations of the visible debris plume from a more oblique view, the angles and velocities of the ejecta from this unique cratering experiment are better constrained. Here we report the first visible observations of the LCROSS ejecta plume from Earth, thereby ascertaining the morphology of the plume to contain a minimum of two separate components, placing limits on ejecta velocities at multiple angles, and permitting an independent estimate of the illuminated ejecta mass. Our mass estimate implies that the lunar volatile inventory in the Cabeus permanently shadowed region includes a water concentration of 6.3±1.6% by mass.

The formation of molecular hydrogen from water ice in the lunar regolith by energetic charged particles

On 9 October 2009, the Lunar Crater Observation and Sensing Satellite (LCROSS) mission impacted a spent Centaur rocket into the permanently shadowed region (PSR) within Cabeus crater and detected water vapor and ice, as well as other volatiles, in the ejecta plume. The Lyman Alpha Mapping Project (LAMP), a far ultraviolet (FUV) imaging spectrograph on board the Lunar Reconnaissance Orbiter (LRO), observed this plume as FUV emissions from the fluorescence of sunlight by molecular hydrogen (H2) and other constituents. Energetic charged particles, such as galactic cosmic rays (GCRs) and solar energetic particles (SEPs), can dissociate the molecules in water ice to form H2. We examine how much H2can be formed by these types of particle radiation interacting with water ice sequestered in the regolith within PSRs, and we assess whether it can account for the H2 observed by LAMP. To estimate H2formation, we use the GCR and SEP radiation dose rates measured by the LRO Cosmic Ray Telescope for the Effects of Radiation (CRaTER). The exposure time of the ice is calculated by considering meteoritic gardening and the penetration depth of the energetic particles. We find that GCRs and SEPs could convert at least 1–7% of the original water molecules into H2. Therefore, given the amount of water detected by LCROSS, such particle radiation‒induced dissociation of water ice could likely account for a significant percentage (10–100%) of the H2measured by LAMP.

An Overview of the Lunar Crater Observation and Sensing Satellite (LCROSS)

The Lunar Crater Observation Sensing Satellite (LCROSS), an accompanying payload to the Lunar Reconnaissance Orbiter (LRO) mission (Vondrak et al. 2010), was launched with LRO on 18 June 2009. The principle goal of the LCROSS mission was to shed light on the nature of the materials contained within permanently shadowed lunar craters. These Permanently Shadowed Regions (PSRs) are of considerable interest due to the very low temperatures, <120 K, found within the shadowed regions (Paige et al. 2010a, 2010b) and the possibility of accumulated, cold-trapped volatiles contained therein. Two previous lunar missions, Clementine and Lunar Prospector, have made measurements that indicate the possibility of water ice associated with these PSRs. LCROSS used the spent LRO Earth-lunar transfer rocket stage, an Atlas V Centaur upper stage, as a kinetic impactor, impacting a PSR on 9 October 2009 and throwing ejecta up into sunlight where it was observed. This impactor was guided to its target by a Shepherding Spacecraft (SSC) which also contained a number of instruments that observed the lunar impact. A campaign of terrestrial ground, Earth orbital and lunar orbital assets were also coordinated to observe the impact and subsequent crater and ejecta blanket. After observing the Centaur impact, the SSC became an impactor itself. The principal measurement goals of the LCROSS mission were to establish the form and concentration of the hydrogen-bearing material observed by Lunar Prospector, characterization of regolith within a PSR (including composition and physical properties), and the characterization of the perturbation to the lunar exosphere caused by the impact itself.

Modeling of the vapor release from the LCROSS impact: 2. Observations from LAMP

Using a Monte Carlo model, we analyze the evolution of the vapor plume emanating from the Lunar Crater Observation and Sensing Satellite (LCROSS) impact into Cabeus as seen by the Lyman Alpha Mapping Project (LAMP), a far‐ultraviolet (FUV) imaging spectrograph onboard the Lunar Reconnaissance Orbiter. The best fit to the data utilizes a bulk velocity between 3.0 and 4.0 km/s. The fits to the light curve comprised of Hg, Ca, and Mg are not strongly dependent on the temperature. In contrast, the best fit to the light curve from H2 and CO corresponds to a 500 K thermal velocity distribution. The LAMP field of view primarily encounters particles released at low angles to the horizontal and misses fast moving particles released at more vertical angles. The isotropic model suggests that 117 ± 16 kg H2, 41 ± 3 kg CO, 16 ± 1 kg Ca, 12.4 ± 0.8 kg Hg, and 3.8 ± 0.3 kg Mg are released by the LCROSS impact. Additional errors could arise from an anisotropic plume, which cannot be distinguished with LAMP data. Mg and Ca are likely incompletely volatilized owing to their high vapor temperatures. The highly volatile components (H2 and CO) might derive from a greater mass of material. To agree with predicted abundances by weight of 0.047%, 0.023%, 11%, 0.28% and 3.4% for H2, CO, Ca, Hg, and Mg, respectively, the species would be released from 250,000 kg, 180,000 kg, 140 kg, 4400 kg, and 110 kg of regolith, respectively. This is consistent with the relative volatility of these species.

Scouring the surface: Ejecta dynamics and the LCROSS impact event

The Lunar CRater Observation and Sensing Satellite mission (LCROSS) impacted the moon in a permanently shadowed region of Cabeus crater on October 9th 2009, excavating material rich in water ice and volatiles. The thermal and spatial evolution of LCROSS ejecta is essential to interpretation of regolith properties and sources of released volatiles. The unique conditions of the impact, however, made analysis of the data based on canonical ejecta models impossible. Here we present the results of a series of impact experiments performed at the NASA Ames Vertical Gun Range designed to explore the LCROSS event using both high-speed cameras and LCROSS flight backup instruments. The LCROSS impact created a two-component ejecta plume: the usual inverted lampshade “low-angle” curtain, and a high speed, high-angle component. These separate components excavated to different depths in the regolith. Extrapolations from experiments match the visible data and the light curves in the spectrometers. The hollow geometry of the Centaur led to the formation of the high-angle plume, as was evident in the LCROSS visible and infrared measurements of the ejecta. Subsequent ballistic return of the sunlight-warmed ejecta curtain could scour the surface out to many crater radii, possibly liberating loosely bonded surface volatiles (e.g., H2). Thermal imaging reveals a complex, heterogeneous distribution of heated material after crater formation that is present but unresolved in LCROSS data. This material could potentially serve as an additional source of energy for volatile release.

Modeling of the vapor release from the LCROSS impact: Parametric dependencies

[1] The Lunar Crater Observation and Sensing Satellite (LCROSS) mission included an intentional impact into the Cabeus crater, a permanently shadowed region near the Moon's south pole. The impact produced a vapor plume of volatile species liberated from the impact site. Using a Monte Carlo model to simulate the vapor plume expansion, this paper investigates the expansion as a function of the physical properties of the gas. For a thermal release scenario, the cloud expands with the highest density at the center, with the density dropping within the cloud in time as the cloud expands. When a significant non-thermal component to the velocity (a bulk speed) exists, the vapor expands as a hemispheric shell outward from the impact site. For heavier species, the high bulk velocity produces a hemisphere of higher density of gas that appears as a ring from above. For lighter gases like H2, the thermal velocity is on the same order as the bulk velocity. If the source is prolonged, the source rate is dominant in determining the local density, however. Gases produced by photodissociation have a prolonged source close to the impact site compared to promptly produced vapors.

Results from the NMSU-NASA Marshall Space Flight Center LCROSS observational campaign

[1] We observed the Lunar Crater Observation and Sensing Satellite (LCROSS) lunar impact on 9 October 2009 using three telescope and instrument combinations in southern New Mexico: the Agile camera with a V filter on the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory (APO), a StellaCam video camera with an R filter on the New Mexico State University (NMSU) 1 m telescope at APO, and a Goodrich near-IR (J and H band) video camera on the NMSU 0.6 m telescope at Tortugas Mountain Observatory. The three data sets were analyzed to search for evidence of the debris plume that rose above the Cabeus crater shortly after the LCROSS impact. Although we saw no evidence of the plume in any of our data sets, we constrained its surface brightness through analysis of our photometrically calibrated data. The minimum surface brightness that we could have detected in our Agile data was 9.69 magnitudes arc sec−2, which is 177 times fainter than the brightest part of the foreground ridge of Cabeus. In our near-IR data, our minimum detectable surface brightness was 8.58 magnitudes arc sec−2, which is 370 times fainter than the brightest part of the foreground ridge in the J and H bands. The debris plume was detected by the LCROSS shepherding spacecraft and the Diviner radiometer on the Lunar Reconnaissance Orbiter. Given the plume radiance observed by LCROSS, we cannot distinguish between a conical or cylindrical plume geometry because when seen from Earth, both are below our detection thresholds.

A ground-based observation of the LCROSS impact events using the Subaru Telescope

The Lunar Crater Observation and Sensing Satellite (LCROSS) mission was an impact exploration searching for a volatile deposit in a permanently shadowed region (PSR) by excavating near-surface material. We conducted infrared spectral and imaging observations of the LCROSS impacts from 15 min before the first collision through 2 min after the second collision using the Subaru Telescope in order to measure ejecta dust and water. Such a ground-based observation is important because the viewing geometry and wavelength coverage are very different from the LCROSS spacecraft. We used the Echelle spectrograph with spectral resolution λ/Δ λ ∼ 10,000 to observe the non-resonant H 2O rotational emission lines near 2.9 μm and the slit viewer with a K′ filter for imaging observation of ejecta plumes. Pre-impact calculations using a homogeneous projectile predicted that 2000 kg of ejecta and 10 kg of H 2O were excavated and thrown into the analyzed area immediately above the slit within the field of view (FOV) of the K′ imager and the FOV of spectrometer slit, respectively. However, no unambiguous emission line of H 2O or dust was detected. The estimated upper limits of the amount of dust and H 2O from the main Centaur impact were 800 kg and 40 kg for the 3 σ of noise in the analyzed area within the imager FOV and in the slit FOV, respectively. If we take 1 σ as detection limit, the upper limits are 300 kg and 14 kg, respectively. Although the upper limit for water mass is comparable to a prediction by a standard theoretical prediction, that for dust mass is significantly smaller than that predicted by a standard impact theory. This discrepancy in ejecta dust mass between a theoretical prediction and our observation result suggests that the cratering process induced by the LCROSS impacts may have been substantially different from the standard cratering theory, possibly because of its hollow projectile structure.