Neil Bowles

Abstract:

Abstract Intermittently sunlit areas near the lunar south pole are estimated to harbor thermal conditions permitting long‐term stability of water ice and other volatiles. They are targets for future science and exploration missions due to the combination of sunlight availability for solar power generation, and the possibility for extraction of volatiles for scientific analysis and ISRU. We construct a geodatabase of spatially co‐registered remote sensing and thermal model results, and perform a probabilistic analysis to determine the likelihood of successfully landing and operating on such locations for a quadrangular study area that bounds the 80°S parallel. In addition to water ice thermal stability, we consider factors relevant for the operation of solar‐powered landed spacecraft: visibility to the Earth, visibility to the sun, and local slope. For two scenarios representing sets of most‐ and least‐constrained landing site requirements, we find that circular landing ellipse diameters of ∼0.9 and 2.6 km, respectively, would allow to target available compliant terrains with 100% success. We quantify the reduction in success probability with increasing landing ellipse size. Further, we explore the distributions of geometric properties of compliant areas, and identify three sites of interest that support large areas of compliant terrain: near De Gerlache crater, near Shackleton crater, and Mons Mouton (informally named as Leibnitz‐β massif). This study is provided to support planning for future lunar missions. Plain Language Summary Researchers have identified areas near the lunar poles that receive occasional sunlight and could keep water ice and other resources stable over a long period of time. These spots are valuable for future lunar missions since they could provide solar power and possibly resources such as water for scientific study and on‐site use. To assess potential landing sites in the south polar region, we created a database combining remote sensing and thermal data set, then used it to calculate the likelihood of successful landing on accessible terrains with stable water ice conditions from the 80°S to the South Pole. The study looked at factors critical for solar‐powered landers: the terrain's visibility to Earth (for communication), sunlight access, and the slope of the ground. We analyzed two scenarios with different landing precisions. We found that landing areas with diameters of about 0.9 and 2.6 km could ensure a 100% success rate under the most‐ and least‐constrained scenarios, respectively. Larger landing areas decreased the success probability. We also mapped the physical characteristics of ideal areas and highlighted three promising locations near De Gerlache crater, Shackleton crater, and Mons Mouton. Key Points We identify intermittently sunlit areas that permit long‐term stability of sub‐surface water ice, and accessible by landed missions “Compliant terrains” in two scenarios range from 13,071 km² (least constrained) to 290 km² (most constrained) in the south polar region For areas ≥80°S, we recommend sub‐km landing precision for missions with success criteria involving exploration of lunar polar water ice

Abstract:

Research into compositions of small bodies and planetary surfaces, such as asteroids, is key to understanding the origin of water and organics on Earth [1], as well as placing constraints on planetary dynamics and migration models [2] that can help understand how planetary systems around other stars may form and evolve. Compositional estimates can be found with thermal infrared (TIR; 5-25μm) spectroscopy, as the TIR region is rich in diagnostic information and can be used in remote sensing observations and laboratory measurements. However, TIR spectra of the same material may appear differently depending on several factors, such as particle size, surface roughness, porosity etc. This work quantifies the changes in spectral morphology (i.e., shapes and depths of spectral features) as particle size transitions from fine (90%), at several size fractions, aimed to be

Abstract:

Introduction: Enceladus Thermal Mapper (ETM) is an Oxford-built high-heritage instrument that is being developed for outer solar system operations. ETM is based upon the design of Lunar Thermal Mapper (LTM, launched on Lunar Trailblazer, Fig. 1). It has a strong heritage story, including MIRMIS (on Comet Interceptor), Compact Modular Sounder (on TechDemoSat-1) and filters shared with Lunar Diviner (on Lunar Reconnaissance Orbiter). ETM is a miniaturized thermal infrared multispectral imager, with space for 15 spectral channels (bandpasses) that can be tailored to the mission requirements. It consists of a five-mirror telescope and optical system and an uncooled microbolometer detector array. Real-time calibration is achieved using a motorized mirror to point to an onboard blackbody target and empty space. ETM has an IFOV of 35 mm, so assuming a 100 30 km orbit it will have a spatial resolution of 40 to 70 m/pixel and a swath width of 14 - 27 km. ETM Updates: Through UK Space Agency funding we have developed three areas of ETM: its filter profile, radiation tolerance and sensitivity to Enceladus-like surfaces. Filters: ETM is a push broom thermal mapper, which works by the detector being swept over a surface. Each of the detector’s 15 channels is made up 16 rows, which are coadded to increase the signal to noise. A recently completed preliminary study has updated ETM’s bandpasses to include filters between 6.25 mm and 200 mm to enable it to detect Enceladus’ polar winter (170 K). Depending on the mission goals not all channels need to be utilised to achieve this, making some available for additional studies (e.g. searching for salt). Radiation: The radiation environments of Enceladus are vastly different to those of the Moon. Recent radiation testing and analysis showed that the majority of ETM’s existing design is already highly radiation tolerant. With some additional shielding and one component change all parts can reach the radiation hardness required to operate in the Saturn-system. The additional shielding may be provided by the spacecraft structure, depending on the adopted design. Sensitivity: ETM’s sensitivity to cryogenic surfaces is currently predicted through a well-characterised model. However, as part of the LTM calibration campaign we plan to directly measure its sensitivity to

Abstract:

Introduction: The origins of Mars' moons, Phobos and Deimos, remain uncertain, with two main hypotheses under consideration: formation from debris following a high-energy impact between Mars and an asteroid [1], or capture of primitive asteroids [2]. To address this, JAXA's Martian Moons eXploration (MMX) mission aims to return samples from Phobos by 2031 [3]. The characterisation of these samples will determine the origin of Phobos.To ground-truth remote observations of Phobos, we have used X-ray diffraction (XRD), and Fourier transform infrared (FTIR) reflectance spectroscopy to characterise the bulk mineralogy and IR spectral properties of ureilites, carbonaceous and ordinary chondrites, the composition of which could be indicative of a captured asteroid [4], and Martian meteorites that could represent a collisional formation. By acquiring XRD and IR data from the same material, mineral abundances can be directly correlated with features in reflectance spectra [5]. When MMX reaches Phobos, meteorite data collected in the laboratory will play a crucial role towards interpreting the mineralogy and composition of materials on its surface.Methods: We have characterised the mineralogy and spectral properties of six CM (Mighei-like) carbonaceous chondrites, Tarda (C2-ung), the CO (Ornans-like) chondrite Kainsaz, a range of shock darkened ordinary chondrites (mostly falls) including L4-6, and H5-6, four CR2 chondrites, four ureilites, Martian meteorites Nakhla and Tissint, and a Tagish Lake (C2-ung) based simulant created by the University of Tokyo, known as UTPS-TB [6]. For the meteorites, chips of approximately 200 mg were ground to produce powders with grain sizes of less than 40 microns. The UTPS-TB sample came in a powdered form which was ground to the same grain size as the meteorites.Diffuse reflectance spectra (1.7 - 50 μm) were collected using a Bruker VERTEX 70V FTIR spectrometer at the University of Oxford Planetary Spectroscopy Facility. Spectra were calibrated at the start of each measurement day and between measurements of samples using a gold standard. The powdered sample was measured under a vacuum to reduce terrestrial atmospheric contributions.XRD patterns of the same powders were collected using an INEL X-ray diffractometer with a position-sensitive detector at the Natural History Museum, London. Around 50 mg of powdered sample was measured for 16 hours to achieve good signal-to-noise. Measurements of well-characterised standard minerals were collected for 30 minutes and compared with meteorite patterns to identify minerals and quantify their abundance in the sample [e.g. 7].Results & Discussion: The mineralogical and spectral characteristics of meteorites in this investigation are compared the reflectance spectra of Phobos’ surface. The CR chondrites are primitive, containing both anhydrous silicates (e.g. olivine and pyroxene) and aqueous alteration phases such as phyllosilicates, carbonates, magnetite, and sulfides. Their albedo is ~3-5% reflectance with a weak red slope in the visible to near-infrared (VNIR). The CRs have a 3 μm hydration band, due to partial aqueous alteration. Their low VNIR reflectance, red-sloped continuum, and weak 3 μm spectral absorption feature is like that of Phobos, supporting the captured asteroid origin theory. The CM chondrites share similar spectral features but have a lower albedo and a stronger μm hydration band, corresponding to a higher phyllosilicate composition.   The ureilites are achondritic ultramafic meteorites containing olivine, pyroxene and carbon phases. These samples have a low albedo (~6-15% in VNIR) due to their opaque carbonaceous composition. However, their VNIR spectra are blue-sloped, inconsistent with Phobos’ red-sloped spectra. Ureilites are also anhydrous and therefore lack the 3 μm hydration band seen in Phobos spectra. Their low reflectance and feature-poor spectra could resemble Phobos, however there is a significant difference in spectral slope and hydration features. Therefore, Phobos were composed of ureilitic material, its surface would need to be significantly modified by space weathering.Martian meteorites Nakhla (a nakhlite) and Tissint (a shergottite) have mineralogical and spectral features consistent with their basaltic origin. XRD measurements of these meteorites are dominated by pyroxene (augite, pigeonite), and olivine, consistent with their origin in the Martian crust. Their reflectance spectra have relatively high albedo, mafic absorption bands at ~1 and 2 μm, and a lack of hydration features. These features are inconsistent with the spectra of Phobos, which lack 1 or 2 μm bands and show significantly lower reflectance.CR and CM chondrites are the closest spectral match to Phobos from the samples studied. Their low albedo, red-sloped, hydrated spectra are consistent with surface measurements of Phobos. Ureilites share low reflectance but differ significantly in slope and hydration, while Martian meteorites differ in more spectral characteristics. These results support the interpretation that Phobos is composed of primitive, carbon-rich material, likely of outer solar system origin, and favour a capture scenario over a collisional formation from Martian ejecta. The similarities between the carbonaceous chondrites and Phobos indicates that the Martian moons may be captured asteroids and further demonstrates the importance of the MMX mission sample return for solving the mystery of their origin definitively.References: [1] R. Citron et al. (2015) Icarus 252:334-338. [2] M. Pajola et al. (2013) The Astrophysical Journal 777:127. [3] K. Kuramoto et al. (2022) Earth, Planets and Space 74:12. [4] K. D. Pang et al. (1978) Science 199(4324):64-66. [5] H. C. Bates et al. (2023) Meteoritics & Planetary Science 1-23. [6] H. Miyamoto et al. (2021) Earth, Planets and Space 73:1-17 [7] G. Cressey et al. (1996) Powder Diffraction 11:35-39.