USA – Sottosuolo lunare alla ribalta – L’esplorazione delle grotte lunari al centro dell’importante incontro scientifico dell’AGU American Geophysical Union – Advancing Earth and Space Science.
A new Orleans, dal 13 al 17 dicembre 2021, si è svolto l’incontro autonnale dell’American Geophysical Union a new Orleans. Durante l’incontro, insieme a molte relazioni su diversi studi scientifici sul nostro satellite, è stato presentato uno studio dell’Università del Colorado at Boulder che attraverso simulazioni al computer ha verificato la possibili condizioni all’interno delle grotte lunari.
La Luna può sembrare una distesa brunastra uniforme, ma guardandola da vcino è possibile trovare asperità e fessure sulla superficie, da profonde trincee a pozzi e forse anche grotte.
I ricercatori della Colorado University at Boulder hanno deciso di provare come potrebbe essere l’ambiente, all’interno di alcune di queste cavità oscure, molte delle quali sono troppo buie per essere viste chiaramente dall’orbita.
I risultati preliminari del team, suggeriscono che pozzi e grotte sulla Luna mostrano condizioni notevolmente stabili.
Secondo Andrew Wilcoski, uno studente laureato presso il Dipartimento di Scienze Astrofisiche e Planetarie della CU Boulder, le grotte lunari non sembrano subire i forti sbalzi di temperatura che sono comuni sulla superficie lunare.
“Se vogliamo mandare persone in queste grotte nei decenni a venire, vogliamo sapere cosa si dovranno aspettarsi laggiù”, ha detto Wilcoski, coautore della nuova ricerca.
Il messaggio è: com’è andare a fare la speleologia sulla luna?
I futuri esploratori lunari dovranno partire preparati. Pozzi e caverne, ha spiegato Wilcoski, sono luoghi potenzialmente ideali per le colonie spaziali del futuro. Le loro sale e corridoi sono naturalmente accoglienti e potrebbero proteggere gli esseri umani dalle pericolose radiazioni del sole.
Alcuni scienziati si sono anche chiesti se le fosse lunari e le grotte potrebbero essere ricche di risorse naturali fondamentali per la lunga permanenza umana sulla Luna. Ghiaccio d’acqua, che gli esploratori potrebbero estrarre per raccogliere acqua da bere, per lavarsi e persino come carburante per missili.
Per scoprirlo con certezza, Wilcoski e lo scienziato planetario Paul Hayne hanno effettuato simulazioni al computer per cercare di ricreare le condizioni sotto la superficie della Luna.
Le loro scoperte iniziali sono contrastanti: gli ambienti stabili delle grotte lunari potrebbero aiutare gli astronauti a superare alcuni degli aspetti più estremi della Luna. Quelle stesse condizioni, tuttavia, potrebbero renderli luoghi tutt’altro che perfetti per la ricerca l’acqua.
“Sono opzioni interessanti per stabilire una presenza umana a lungo termine sulla luna“, ha detto Hayne, un Professore presso il Laboratorio di fisica atmosferica e spaziale della CU Boulder.
Hayne ha aggiunto che nessuno sa quanti pozzi e caverne potrebbero nascondersi sulla Luna. Le ricerche dal 2014 ne hanno trovati più di 200. Molti sembravano buchi rotondi nella superficie lunare e andavano da quasi un chilometro di larghezza alle dimensioni di un autobus a due piani di Londra.
Gli scienziati sono entusiasti del loro potenziale, perché la Luna stessa è un ambiente molto estremo.
“All’equatore, sulla superficie le temperature possono raggiungere più di 100 gradi durante il giorno e scendere fino a -170 gradi durante la notte“, ha detto Wilcoski.
I ricercatori hanno sviluppato simulazioni, per tracciare le temperature in ipotetiche fosse lunari e grotte di varie forme e dimensioni, mentre il sole sorgeva e tramontava sulla luna. L’esposizione e l’orientamento degli ingressi alle cavità ovviamente è molto importante. Se l’ingresso di una grotta punta direttamente verso il sole nascente, ad esempio, diventerà molto più calda che se puntasse da un’altra parte.
Proprio come le grotte sulla Terra, le grotte sulla Luna sembrano essere ambienti relativamente miti.
La maggior parte delle simulazioni fatte dal team ha rilevato temperature da meno 120 a meno 70 gradi Celsius per un intero giorno lunare.
Coddizioni sfavorevoli per l’acqua congelata nel ghiaccio, ha detto Wilcoski.
Precedenti ricerche di Hayne e altri scienziati, hanno dimostrato che il ghiaccio d’acqua potrebbe essersi accumulato nel corso di miliardi di anni in alcuni siti sulla Luna, che i ricercatori chiamano “trappole fredde”. Ma, in base ai risultati delle simulazioni, molte caverne lunari sono probabilmente troppo calde per ospitare simili tesori.
“Una possibilità interessante sarebbe quella di stabilire una stazione base protetta, all’interno di un pozzo lunare o di una grotta vicino a uno dei crateri polari contenenti ghiaccio d’acqua“, ha detto Hayne. “Gli astronauti potrebbero avventurarsi fuori dalle grotte quando le condizioni lo permettono, per raccogliere terreno ricco di ghiaccio”.
Ecco gli altri temi affrontati durante l’incontro:
-The Science of Exploration: The Moon and Beyond III Oral
-Thermal Environments and Volatile-trapping Potential of Lunar Pits and Caves
-The Effects of Impact Angle on Lunar Water Retention by Micrometeoroid Impact
-Investigating the Distribution of Lunar Polar Volatiles Using Mini-RF Surface Roughness Data
-LRO-LAMP Investigations of Cold Trapped Volatiles at the Lunar South Pole
-An Exogenic Origin for the Volatiles Sampled by the LCROSS Impact
-Lunar-Laser-Lab for Volatiles INvestigation. A CLPS-compatible Instrument for In-situ Resource Exploration
-Lunar Trailblazer: A Pioneering Smallsat for Lunar Water and Lunar Geology
P53B – The Science of Exploration: The Moon and Beyond III Oral
A close collaboration between science, technology and exploration enables deeper understanding of the Moon and other airless bodies as we move beyond low-Earth orbit. The Solar System Exploration Research Virtual Institute (SSERVI) focuses on the scientific aspects of exploration as they pertain to the Moon, Near Earth Asteroids (NEAs) and the moons of Mars. In the broader context of the current Moon to Mars initiative, this session will feature interdisciplinary, exploration-related science centered around these airless bodies targeted as potential human destinations. Areas of study span a broad spectrum of lunar, NEA, and Martian moon science encompassing investigations of the surface, interior, exosphere, and near-space environments as well as science uniquely enabled from these bodies. Graduate students and early career researchers are particularly encouraged to submit for oral presentations.
P53B-01 – Thermal Environments and Volatile-trapping Potential of Lunar Pits and Caves
The Moon is host to numerous pits and caves located in varied terrains across its surface including mare basalt, impact melt deposits, and highland terrain (Wagner and Robinson, 2014). Lunar pits have great potential both as scientific targets and for resources during future human exploration. They have the potential to provide insights into the volcanic and impact history of the Moon, as well as shelter from temperature extremes, micrometeorite bombardment, and radiation on the lunar surface. Of particular interest is their potential to sequester significant deposits of volatiles, including water. Although low-to-mid latitude pits are likely too warm to cold-trap volatiles, possible pits at high latitudes (Lee, 2018; Avent and Lee, 2021) may have the geometries and temperatures necessary for a number of volatile species to remain stable over geologic time. Therefore, knowledge of the thermal environments of lunar pits and the existence and composition of volatiles within these pits could help answer questions about the history of volatiles on the Moon.
We develop a 3D thermal model to characterize the temperature environments within lunar pits and caves, with the ultimate goal of assessing the stability of a range of volatile species within these pits. The model is initialized with a 3D surface composed of triangular facets of variable size. The model balances 1D heat conduction on each facet with direct insolation, infrared emission, and multiple-scattering of both visible and infrared radiation, and also accounts for the effects of terrain shadowing within lunar pits. Model output is validated against thermal observations of known lunar pits made by the Diviner Lunar Radiometer Experiment onboard the Lunar Reconnaissance Orbiter.
We examine how pit interior temperatures depend on pit geometry and latitude. High latitude pits may provide thermal environments cold enough to trap volatiles. The next iteration of the model will include a coupled Monte Carlo ballistic “hopping” model that will evaluate the residence times and equilibrium vapor pressures of volatiles within pits. The ballistic model will allow the assessment of the effects of pit geometry and latitude on the trapping of a range of different volatile species, and predict the compositions of concentrated volatiles that may exist within lunar pits.
P53B-02 – The Effects of Impact Angle on Lunar Water Retention by Micrometeoroid Impact
Micrometeoroid impact has been considered a major source for lunar water formation. Recent laboratory experiments and molecular dynamics simulations have shown that micrometeoroid impact can provide the energy required to change the hydroxyl groups formed by solar wind implantation to water molecules. While the impact can initiate the reactions to form water molecules, the high temperature and mechanical collisions during the impact can also eject or desorb water molecules to the space. Hence, micrometeoroid impacts can also contribute negatively to lunar water retention.
The impact angle determines the size of the crater as well as the gardening depth, two very important factors that can directly affect water retention. In this study we use atomic scale simulation to investigate the effect of impact angle on lunar water retention during the micrometeoroid impact. Both the impact angle distribution and the surface roughness are included to determine the net effect of micrometeoroid impact on lunar water formation from the birth of the moon till present.
P53B-03 – Investigating the Distribution of Lunar Polar Volatiles Using Mini-RF Surface Roughness Data
Questions surrounding the presence, distribution, and nature of volatiles, such as water, at the lunar poles have driven much of lunar science over the past two decades. A multitude of datasets have suggested the presence of water both at volumetric depth, and as surficial frost; and data from the LCROSS impactor directly attests to the presence of water at the Moon’s south pole. However, despite highly suggestive data acquired from a number of different instruments, results from radar exploration of the Moon have remained ambiguous.
Recent studies combining Diviner-derived ice stability zones and LOLA surface roughness has suggested that there is a correlation between regions of ice stability and regions of decreased surface roughness. Motivated by this, we undertook an investigation of lunar polar surface roughness using a controlled Mini-RF monostatic circular polarization ration (CPR) south polar mosaic. We investigated 42 south polar craters and 7 background regions, and divided the craters by floor illumination into fully PSR (permanently shaded region), no PSR, and mixed. Our results showed that non-PRS craters had consistently higher CPR than fully PSR and mixed PSR craters. Amongst the mixed and fully PSR craters, a smaller subset of craters emerged with significantly lower CPRs than standard low-roughness lunar regions. The lowest CPR craters include Sverdrup, Laveran, an unnamed crater at 168.4° E, 88.7° S, both the PSR and non PSR portions of the floors of Cabeus and Cabeus B, and a non-crater floor background region near Sverdrup. The magnitude of CPR difference between these exceptionally smooth polar craters and standard low-roughness lunar regions is similar in magnitude to the difference between standard low-roughness lunar regions and the roughest average lunar regions. This suggests that the CPR deviations observed in these craters are both highly unusual, and significant. We hypothesize that these crater floor regions — that include the floor of Cabeus crater sampled during the LCROSS mission—are the result of an enhanced volatile presence in the regolith. Continued analysis will help to determine if this signature is the result of a low-porosity intimate mixture of water ice and regolith, near surface smoothing resulting from deeply buried ice lenses, or another previously unrecognized process.
Using Mini-RF circular polarization data (CPR) we investigated the surface roughness of 41 lunar south polar craters, divided by the presence or absence of permanently shadowed regions on the crater floor. Our analysis revealed 5 craters with exceptionally low surface roughness. The magnitude of CPR difference between these exceptionally smooth south polar craters is similar in magnitude to the difference between the smoothest lunar equatorial regions and the roughest lunar highlands regions. This suggests that the observed deviation is both highly unusual and significant. We hypothesize that the decreased surface roughness of these crater floors is intimately related to the presence of volatile species, such as water ice. This research provides a new look at the potential distribution of water ice at the lunar south pole.
P53B-04 – LRO-LAMP Investigations of Cold Trapped Volatiles at the Lunar South Pole
The Lyman Alpha Mapping Project (LAMP) UV spectrograph, onboard the Lunar Reconnaissance Orbiter, has provided lunar surface and exospheric observations for over a decade. Observations have included regions of interest such as permanently shadowed regions (PSRs) at the south pole. Cold traps within PSRs are considered regions of interest partially due to their ability to sequester volatiles such as H2O. In this study, we accumulated south pole observations from the start of the science phase of the mission in mid-September 2009 through early-October 2016. We expand upon similar previous LAMP PSR studies by more than doubling the data used in previous analyses, increasing the signal to noise of the dataset, and incorporating improved data quality filtering. We focus our study on five craters: Faustini, Shoemaker, Haworth, Cabeus, and Amundsen. Additionally, we investigate a region adjacent to Shoemaker and Haworth which is thermally capable of cold trapping H2O. We observe lower albedos within the cold trap regions than in the surrounding non-cold trap regions across all wavelengths, indicative of increased regolith porosity within cold traps. We additionally find areas of high Off-band (175 nm – 190 nm) to On-band (148 nm – 162 nm) albedo ratio (the UV wavelength ranges with high and low H2O ice reflectivity, respectively) within cold traps, which is consistent with the presence of water ice. We find further evidence of cold trapped volatiles by examining Off-band/On-band ratios with annual maximum temperature. An increase in Off-band/On-band ratio at ~120 K is further indicative of volatile stability timescales on the order of 1 Myr.
P53B-05 An Exogenic Origin for the Volatiles Sampled by the LCROSS Impact
The Moon is recognized as a cornerstone for understanding the history of the solar system. Just as the impact history of the Moon helps us to understand the impact history of the Earth and other solar system bodies, the history of volatiles on the Moon can help us to constrain how volatiles were delivered to the Earth-Moon system as well as the development and loss of secondary atmospheres through internal outgassing. The Permanently Shaded Regions (PSRs) of the Lunar poles are known to provide an environment well suited for long-term preservation of volatiles, but the exact abundance and composition of the volatiles present in the PSRs is poorly understood. The greatest insight into the composition of volatiles beyond water ice was provided by the Lunar Crater Observation and Sensing Satellite (LCROSS) mission. Through a re-analysis of the composition measurements, we have determined new constraints on the origin of the volatiles in the top three meters of the Lunar south pole Cabeus Permanently Shaded Region.
P53B-06 – L3VIN: Lunar-Laser-Lab for Volatiles INvestigation. A CLPS-compatible Instrument for In-situ Resource Exploration
L3VIN is a compact laser-induced breakdown spectroscopy (LIBS) instrument that mounts 2.5D spectral mapping and imaging optical assemblies into a compact, plug-and-play package that can be integrated into virtually any small rover or lander to add key new analytical capabilities not available today in planetary sciences: ultra-fast geochemical with no moving parts. L3VIN
uses active laser beam steering technology developed by our team under several NASA SBIR awards [1-2].
As an autonomous, broad utility system with autofocusing and mapping capabilities, L3VIN stands to improve upon spaceflight LIBS systems, enabling high-precision mapping of lunar volatiles and other resources using absolutely no moving parts – L3VIN does not require rotating a mast to raster a region of interest. This concept is revolutionary in that it enables real-time standoff micro-scale survey at micron to cm scales at < 2m distance from the lunar regolith using active laser beam steering technology built in into the instrument. Mounted on a small rover, our innovative LIBS-based architecture will return 20 x 20 cm maps of volatile (and other ISRU-relevant materials) at 1 m distance with < 1mm/pixel resolution in less than 1 h with detection limits 1 wt%. Combined with a mineralogical instrument such as MIR3000, a near-infrared reflectance instrument (see accompanying abstract in this session), L3VIN would enable geochemical and mineralogical information to be obtained from the same spot on the lunar regolith. For example, MIR3000 detection of H2O/OH species can be validated by LIBS detection of H and O emission lines. More broadly, mineralogical information obtained by MIR3000 cam be complemented by chemical information derived from L3VIN. Thus, a compact payload (< 6 kg) combining both instruments can provide unambiguous, ground-truthed characterization and distribution of lunar materials (hydrated/hydrous compounds, minerals, metals, volatiles) in locations of high interest in the south polar region and the Gruithuisen Domes (see accompanying abstract in this session).  https://sbir.nasa.gov/SBIR/abstracts/19/sbir/phase2/SBIR-19-2-S1.07-2925.html
Our instrument mounts spectral mapping and imaging optical assemblies into a compact, plug-and-play package that can be integrated into virtually any small rover or lander to add key new analytical capabilities not available today in planetary sciences: ultra-fast geochemical with no moving parts.
As an autonomous, broad utility system with autofocusing and mapping capabilities, the instrument improves upon similar systems, enabling high-precision mapping of lunar volatiles and other resources using absolutely no moving parts. This is, the instrument does not require rotating a mast to raster a region of interest. This concept is revolutionary in that it enables real-time micro-scale survey at micron scales at a distance from the lunar regolith using active laser beam steering technology.
Mounted on a small rover or lander, our instrument can characterize and map the distribution of lunar materials (hydrated/hydrous compounds, minerals, metals, volatiles) in locations of high interest in the south polar region and the Gruithuisen Domes.
P53B-07 – Lunar Trailblazer: A Pioneering Smallsat for Lunar Water and Lunar Geology
Lunar Trailblazer is a NASA SIMPLEx small satellite science mission for understanding the Moon’s water and water cycle. Identification of water, determining its form and abundance, and mapping the distribution of water ice and geologic units at spatial scales relevant to robotic and human exploration provide critical knowledge as lunar surface exploration moves forward.
Trailblazer simultaneously measures composition, temperature, and thermophysical properties from a 100+/-30 km lunar polar orbit at high spatial and spectral resolution over select areas of the lunar surface. The objectives are to detect and map water on the lunar surface at key targets to (1) determine its form (OH, H2O or ice), abundance, and local distribution as a function of latitude, soil maturity, and lithology on the sunlit Moon; (2) assess possible time-variation in lunar water on sunlit surfaces; (3) use terrain-scattered light to determine the form, abundance, and distribution of exposed water in permanently shadowed regions; and (4) collect thermal data to understand how local gradients in albedo and surface temperature affect ice and OH/H2O concentration, including the potential identification of new cold traps. While achieving these objectives, Trailblazer will perform the highest-to-date spatial resolution compositional and thermophysical properties mapping and conduct reconnaissance of potential future landing sites.
Lunar Trailblazer’s international team is led by Caltech and managed by JPL. A Lockheed Martin-built and integrated ~200 kg smallsat carries two instruments: (1) JPL’s High-resolution Volatiles and Minerals Moon Mapper (HVM3) shortwave infrared imaging spectrometer (<70 m/pixel, 0.6-3.6 ?m, 10 nm spectral resolution) and (2) the UK-contributed, University of Oxford-built Lunar Thermal Mapper (LTM) multispectral thermal imager (<50 m/pixel, 4 broadband thermal channels 6-100 ?m, 11 compositional channels 7-10 ?m). Selected in June 2019 and confirmed in November 2020, Lunar Trailblazer passed its Critical Design review in July 2021. The integrated Lunar Trailblazer flight system will be delivered in late fall 2022. An ESPA Grande rideshare, Lunar Trailblazer has been manifested by NASA as a secondary payload on the 2025 IMAP launch and is thus scheduled to begin its science phase at the Moon in summer 2025. Plain-language Summary Lunar Trailblazer is a NASA small satellite mission to the Moon, scheduled to complete its flight system in 2022. Lunar Trailblazer will map the lunar surface to determine where there is water on the Moon. Water ice is particularly important as a science exploration target for future landed missions and as a resource for human explorers. The type, amount, and distribution of water as well as the temperature and composition of the Moon's surface will be measured by Lunar Trailblazer, using two infrared imaging instruments that measure reflected radiation from the sun and thermally emitted radiation. This presentation will provide an update on mission status as of December 2021. P53B-08 - The Volatiles Investigating Polar Exploration Rover (VIPER) Mission: Measurement Goals and Traverse Planning A critical goal to both science and exploration is to understand the form and location of lunar polar volatiles. The lateral and vertical distributions of these volatiles inform us of the processes that control the emplacement and retention of these volatiles, as well as helping to formulate in-situ resource utilization (ISRU) architectures. While significant progress has been made from orbital observations, measurements at a range of scales from centimeters to kilometers across the lunar surface are needed to generate adequate “volatile resource models” for use in evaluating the resource potential of volatiles at the Moon. VIPER is a solar and battery powered rover mission designed to operate over multiple lunar days, traversing 10s of kilometers as it continuously monitors for subsurface hydrogen and other surface volatiles. In specific thermal terrain types, including permanently shadowed terrain and locales that permit near-surface ice stability, subsurface samples will be examined for volatile content using a one-meter drill. This talk will provide an overview of the VIPER mission which is scheduled for flight to the Lunar South Pole in late 2023. Fonti: https://agu.confex.com/agu/fm21/meetingapp.cgi/Session/134793