Planetary surfaces

Abstract:

Introduction: Mimas is a small moon of Saturn with a heavily cratered surface and high eccentricity, suggesting an inactive past. It was, thus, surprising when Cassini measurements of Mimas’ libration and tracking of its pericenter precession revealed that Mimas maintains an ocean under an ice shell 20-30 km thick [5,12]. Subsequent investigations into how an ocean-bearing Mimas could have avoided developing tidally-driven fractures [7], its tidal heating budget  [8], constraints on shell thickness from the formation of the Herschel impact basin [3], and thermal-orbital evolution models [5,9] all point to a young ocean that has emerged within the past 10-15 Myr. These results suggest that Mimas may possess the youngest ocean in the Solar System, making it an important target for understanding the early stages of ocean development – such as for Enceladus’ ocean – and the habitability of ocean worlds through time. Uranus’ moon, Miranda, may also have developed an ocean relatively late in its history (e.g., [2]); understanding the evolutionary and geophysical processes at Mimas may help prepare us for a future mission to the Uranian system.Here, we expand upon past work [8,9], in which we relied on globally-averaged tidal heating and constant surface temperature, to develop a map of plausible ice shell thicknesses and surface heat flows on Mimas assuming a present-day ocean. Our goals are to determine the variability in heat flow and ice shell thickness that result from spatial differences in surface temperature and strength of the tide and to quantify requirements that would enable ocean detection via heat flow measurements. Our results also provide estimates of tidal power, which affect the circularization timescale and ocean lifetime within thermal-orbital evolution models.Methods: We utilize the numerical toolkit MATH [13] to compute tidal heating within Mimas’ ice shell and identify the equilibrium ice shell thickness and surface heat flux at a suite of locations across Mimas. These calculations depend on the surface temperature and the basal heat flux. Here, we develop a surface temperature map based on models of solar insolation, and informed by Cassini measurements (e.g., [4]), to obtain robust temperatures. We then vary the basal heat flux across a range that encompasses minimal heating from only radiogenic decay to high heat fluxes associated with dissipation in Mimas’ rocky interior. We use the inferred ice shell thickness of 20-30 km [5,12] to determine the basal heating cases that provide consistent results. From these maps, we can deduce the precision needed to use heat flow measurements to differentiate between a fully frozen Mimas, which likely produces endogenic heat flows of ~1 to several mW/m2 (e.g., [9]), and an ocean-bearing Mimas.The ice shell thickness maps can also be used to compute the tidal dissipation associated with Mimas’ present-day orbit and interior structure. We will input these values into the numerical toolkit PISTES [11] to assess the extent to which Mimas’ ice shell evolution can occur over a longer timescale and/or begin at a higher eccentricity than in past models. These results are particularly important for understanding how Mimas came to possess an ocean. While we expect that Mimas’ ocean emerged due to a recent eccentricity-pumping event that increased its eccentricity to the point of melting, the cause and details are not well-understood. A gap in Saturn’s rings, known as the Cassini Division, appears to record Mimas’ phase of inward migration and increasing eccentricity [1,6]. However, models of this process require Mimas to reach a much higher eccentricity than the thermal-orbital evolution models predict; Mimas’ entire ice shell would have melted in that case, which is inconsistent with its geologic record (see discussion in [5]). In addition, the timescales for Mimas’ subsequent outward migration are in conflict. These discrepancies motivate further investigation into Mimas’ thermal-orbital evolution to determine whether the initial conditions and lifetime of the ocean can be extended.Anticipated results: In Figure 1, we show maps of surface heat flow and ice shell thickness for Europa, assuming different basal heating values [10], which we created using the same tools and approach we are now applying to Mimas. We will present similar maps of ice shell thickness and heat flow across Mimas at its present-day eccentricity that are consistent with the inferred average ice shell thickness. We will also present the precision required for future heat flow measurements to detect the ocean and constrain the thickness of the ice shell, which we will compare to our recent Europa results. Finally, we will present revised thermal-orbital evolution models that account for differences in tidal dissipation between the globally-averaged and spatially-variable models of Mimas and discuss the implications of our findings on the development and age of Mimas’ ocean.Figure 1: We show equilibrium ice shell thicknesses (left) and surface heat flows (right) for Europa assuming different values of the basal heat flux (rows) and applying surface temperatures from model fits to Galileo data (see [10]). Variations in tidal strength exert a strong control on the pattern of heat flow while surface temperature creates deviations in the shell thickness map from the purely tidal pattern. We are conducting a similar investigation of Mimas to better understand the current state of its ocean and ice shell, develop measurement requirements, and explore implications for the ocean’s evolution.References: [1] Baillié, K., et al. (2019) MNRAS 486, p. 2933-2946. [2] Beddingfield, C.B. et al. (2022) PSJ 3, 174. [3] Denton, C.A., and A.R. Rhoden (2022) GRL 49, e2022GL100516. [4] Howett, C. J. A., et al. (2020) Icarus 348. [5] Lainey, V., et al. (2024) Nature 626, p. 280 – 282. [6] Noyelles, B., et al. (2019) MNRAS 486, p. 2947–2963. [7] Rhoden, A.R., et al. (2017) JGR – Planets 122, p. 400-410. [8] Rhoden, A. R., & Walker, M. E. (2022) Icarus 376. [9] Rhoden, A. R., et al. (2024a) EPSL 635. [10] Rhoden et al. (2024b) AGU, Abs P23E-3117 [11] Rudolph, M. L., et al. (2022) GRL 49.[12] Tajeddine, R., et al. (2014) Science 346, p. 322–324.  [13] Walker, M. E., & Rhoden, A. R. (2022) PSJ 3, 149.

Abstract:

The Europa Thermal Emission Imaging System (E-THEMIS) on the Europa Clipper spacecraft will investigate the temperature and physical properties of Europa using thermal infrared images in three wavelength bands at 7-14 µm, 14-28 µm and 28-70 μm [Christensen et al., 2024]. The specific objectives of the investigation are to 1) understand the formation of surface features, including sites of recent or current activity, in order to understand regional and global processes and evolution and 2) to identify safe sites for future landed missions. The E-THEMIS radiometric calibration includes removing the thermal emission from the instrument housing, optical elements, and filters using observations of space and an internal calibration flag [Christensen et al., 2024]. On February 28, 2025, the Clipper spacecraft performed a close flyby of Mars for a trajectory gravity assist. Twenty four hours prior to closest approach the spacecraft pointed the E-THEMIS instrument at Mars and performed a sequence that scanned E-THEMIS across the planet at a slew rate of 100 micro-radians per second. This rate is the same as what be used to image Europa during each flyby [Pappalardo et al., 2024]. This activity accomplished two primary objectives: 1) collect images of a well-characterized target (Mars) to validate the E-THEMIS calibration methodology and software prior to the first observations of Europa; and 2) rehearse the data collection procedure that will be used to obtain global observations of Europa.Mars makes an excellent thermal calibration target because it has been extensively studied and characterized by numerous thermal infrared instruments. The E-THEMIS observations were simulated using modeled surface temperatures generated using global maps of thermal inertia albedo made from the MGS TES data [Christensen et al., 2001], together with the krc thermal model [Kieffer, 2013]. The wavelength-dependent atmospheric absorption and emission was modeled using data from the UAE Emirates Mars Mission EMIRS thermal infrared spectrometer [Amiri et al., 2022; Edwards et al., 2021]. EMIRS collects global scans of hyperspectral data from 6-100 µm at 5 and 10 cm-1 spectral sampling at ~200 km spatial resolution [Edwards et al., 2021]. These spectra were resampled from wavenumber to wavelength and weighted by the three E-THEMIS spectral bandpasses to produce 3-band simulated E-THEMIS global images. EMIRS data were not collected simultaneously with the E-THEMIS imaging, but global observations were acquired at the same season and within 5° of latitude, 10° of longitude, and 0.3 H local time of the E-THEMIS data. Fig. 1 shows an example of the nearest EMIRS observation to the E-THEMIS observing conditions of sub-spacecraft latitude=20.3° N, longitude=163.0° E, local time=11.48 H, and Ls=50.5°. A transfer function from the krc-generated surface temperatures and the bandpass-weighted EMIRS data was created by averaging the ratio of forty-five EMIRS observations to the krc-generated surface temperatures. Simulated E-THEMIS observations were produced using the average of these ratios and the krc surface temperatures. The results are given in Fig. 2. The E-THEMIS data could not be transmitted to Earth until Clipper was more than 2 AU from Sun due to spacecraft thermal constraints. As a result the data were received on Earth on May 7, 2025, and the results and an assessment of the E-THEMIS calibration will be discussed.Fig. 1. Measured Mars temperatures. Comparison of temperature globes for surface temperature (krc model) and E-THEMIS-bandpass-weighted EMIRS data for Bands 1, 2, and 3. The EMIRS observations were acquired on Feb. 17, 2025, at a sub-spacecraft viewing geometry of 16.0° N latitude, 174.1° E longitude, 11.60 H local time, and 45.5° Ls. Fig. 2. Simulated E-THEMIS temperature images. The data for each E-THEMIS band were created using the krc model surface temperatures transferred to E-THEMIS wavelength bands using a transfer function derived from EMIRS observations. ReferencesAmiri, H., D. Brain, O. Sharaf, P. Withnell, M. McGrath, M. Alloghani, M. Al Awadhi, S. Al Dhafri, O. Al Hamadi, and H. Al Matroushi (2022), The emirates Mars mission, Space Science Reviews, 218(1), 4.Christensen, P. R., et al. (2001), The Mars Global Surveyor Thermal Emission Spectrometer experiment: Investigation description and surface science results, J. Geophys. Res., 106, 23,823-823,871.Christensen, P. R., J. R. Spencer, G. L. Mehall, M. Patel, S. Anwar, M. Brick, H. Bowles, Z. Farkas, T. Fisher, and D. Gjellum (2024), The Europa Thermal Emission Imaging System (E-THEMIS) Investigation for the Europa Clipper Mission, Space Science Reviews, 220(4), 1-65.Edwards, C. S., P. R. Christensen, G. L. Mehall, S. Anwar, E. A. Tunaiji, K. Badri, H. Bowles, S. Chase, Z. Farkas, and T. Fisher (2021), The Emirates Mars Mission (EMM) Emirates Mars InfraRed Spectrometer (EMIRS) Instrument, Space science reviews, 217, 1-50.Kieffer, H. H. (2013), Thermal model for analysis of Mars infrared mapping, J. Geophys. Res, 116, 451-470.Pappalardo, R. T., B. J. Buratti, H. Korth, D. A. Senske, D. L. Blaney, D. D. Blankenship, J. L. Burch, P. R. Christensen, S. Kempf, and M. G. Kivelson (2024), Science Overview of the Europa Clipper Mission, Space Science Reviews, 220(4), 1-58.

Abstract:

Enceladus maintains its global, unconsolidated ocean around its rocky, porous core by tidal dissipation with Saturn and torque from its resonance with Dione [1].  The active South Polar Terrain (SPT) region is associated with intense concentrations of endogenic heat, but it is the significantly lower-power conductive heat flow that dominates global heat loss as it occurs over the entire surface.  If Enceladus’ global ocean is to be sustained over a significant fraction of its existence, heating rates would have to be balanced endogenic heat loss. Estimates of heating rates from models vary from 1.5-150 GW [2].  The large range results from uncertainty in both the structure of the bodies’ interiors and their evolution.  Ice shell thickness/shape models, which interpret gravity, libration and topographic data, produce global conductive heat loss estimates of around 18-35 GW [3,4,5].Endogenic heat loss from the SPT has been estimated using thermal observations from Cassini Composite Infrared Spectrometer (CIRS) to be between 5-19 GW [6,7,8], resulting in a conventional, combined heat loss estimate of around 50 GW [9].Detecting endogenic heat loss using thermal observations presents a significant challenge, principally relating to limited data coverage and uncertainty about the surface thermal properties but is possible under some circumstances [10].We use thermal observations CIRS to identify endogenic heat at the north pole of Enceladus in the form of conductive heat flow.   From this estimate we can infer global average heat loss.  We are then able to invoke the same mechanisms used to estimate the global average heat loss from ice shell thickness models [5, 9] to characterize the first north polar and global average ice shell thicknesses independently derived from thermal observations.Acknowledgments: This work was made possible through NASA’s support of Cassini Data Analysis Program Grant Number 80NSSC20K0477. References[1] Nimmo, F., Barr, A.C., Behounková, M. and McKinnon, W.B., 2018. The thermal and orbital evolution of Enceladus: observational constraints and models. Enceladus and the icy moons of Saturn, 475, pp.79-94.[2] Lainey, V., Casajus, L.G., Fuller, J., Zannoni, M., Tortora, P., Cooper, N., Murray, C., Modenini, D., Park, R.S., Robert, V. and Zhang, Q., 2020. Resonance locking in giant planets indicated by the rapid orbital expansion of Titan. Nature Astronomy, 4(11), pp.1053-1058.[3] Thomas, P.C., Tajeddine, R., Tiscareno, M.S., Burns, J.A., Joseph, J., Loredo, T.J., Helfenstein, P. and Porco, C., 2016. Enceladus’s measured physical libration requires a global subsurface ocean. Icarus, 264, pp.37-47.[4] Čadek, O., Tobie, G., Van Hoolst, T., Massé, M., Choblet, G., Lefèvre, A., Mitri, G., Baland, R.M., Běhounková, M., Bourgeois, O. and Trinh, A., 2016. Enceladus's internal ocean and ice shell constrained from Cassini gravity, shape, and libration data. Geophysical Research Letters, 43(11), pp.5653-5660.[5] Hemingway, D.J. and Mittal, T., 2019. Enceladus's ice shell structure as a window on internal heat production. Icarus, 332, pp.111-131.[6] Spencer, J.R., Pearl, J.C., Segura, M., Flasar, F.M., Mamoutkine, A., Romani, P., Buratti, B.J., Hendrix, A.R., Spilker, L.J. and Lopes, R.M.C., 2006. Cassini encounters Enceladus: Background and the discovery of a south polar hot spot. science, 311(5766), pp.1401-1405.[7] Howett, C.J.A., Spencer, J.R., Pearl, J. and Segura, M., 2011. High heat flow from Enceladus' south polar region measured using 10–600 cm− 1 Cassini/CIRS data. Journal of Geophysical Research: Planets, 116(E3).[8] Spencer, J.R., Nimmo, F., Ingersoll, A.P., Hurford, T.A., Kite, E.S., Rhoden, A.R., Schmidt, J. and Howett, C.J., 2018. Plume origins and plumbing: from ocean to surface. Enceladus and the icy moons of Saturn, 163.[9] Nimmo, F., Neveu, M. and Howett, C., 2023. Origin and evolution of Enceladus’s tidal dissipation. Space Science Reviews, 219(7), p.57[10] Miles, G., Howett., C., Spencer J., Vol. 16, EPSC2022-1190, 2022, https://doi.org/10.5194/epsc2022-119

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.

Abstract:

Introduction: The Lunar Thermal Mapper (LTM) is a multispectral infrared radiometer, built by the Oxford Physics Instrumentation Group for the Lunar Trailblazer mission; a small satellite launched in February 2025 under NASA’s Small Innovative Missions for Planetary Exploration (SIMPLEx). Trailblazer aims to advance our understanding of the lunar water cycle by mapping surface temperature, water abundance, distribution and form (OH, H2O, ice) and silicate lithology (i.e., Si-O Christiansen spectral feature). LTM was developed to improve upon existing infrared instrumentation in lunar orbit (e.g., Diviner Lunar Radiometer Experiment, hereafter referred to as Diviner) to provide higher resolution temperature estimations and refine interpretations of thermophysical properties at the surface [2, 3]. Accurately determining surface temperatures on airless bodies is essential for deriving emissivity spectral features (such as the Christiansen Feature and Restrahlen bands, which are diagnostic of silicate lithologies) that are representative of the surface. Temperature errors can affect spectral shape, resulting in the misidentification of surface composition [5, 8].  Our team compared six methods for estimating LTM’s brightness temperature (BT), including the temperature retrieval approach used by Diviner, to (1) determine which method provides the most representative surface temperature and (2) assess how variations in BT estimation affect derived emissivity spectral shape. Despite challenges facing the Trailblazer mission, refining methods for BT estimation remains relevant to the planetary community, as future missions continue to depend on infrared instrumentation and accurate BT retrievals for remote compositional interpretation (e.g., LEAP, L-CIRiS, Europa Clipper).   Instrumentation: LTM is a 15-channel infrared imager that covers a range between 6 to 100 µm [2,3]. LTM advances infrared compositional analysis by incorporating eleven narrowband compositional filters across the 6.25 to 10 µm range. This expanded spectral coverage enables more precise characterization of key features, such as the Christiansen Feature, Reststrahlen bands, and transparency features, which are essential for identifying spectral endmembers (Table 1) [2,3].   LTM builds upon Diviner, a nine-channel instrument that has a broad spectral range from 0.3 to 400 µm (Table 1) [1]. Diviner’s three narrowband compositional channels, 7.55–8.05 µm (Channel 3), 8.10–8.40 µm (Channel 4), and 8.38–8.60 µm (Channel 5), are specifically tuned to capture the Christiansen Feature (CF), an emissivity peak that is diagnostic of broad silicate mineralogy and sensitive to variations in silica content [1,4].  Table 1: LTM and Diviner observational parameters.    Methodology: To assess BT and emissivity retrieval techniques for LTM, we measured four lunar analog samples under controlled laboratory conditions to retrieve high-resolution emission spectra. These laboratory spectra were down-sampled to match LTM’s narrowband spectral resolution. Six BT estimation methods were tested to determine how effectively each method preserved laboratory spectral shape and temperature. The following section describes the laboratory setup and the BT estimation methods examined in this study. Laboratory: Using the PASCALE (Planetary Analogue Surface Chamber for Asteroids and Lunar Environments) in conjunction with a Bruker 70V Fourier Transform Infrared (FTIR) spectrometer, we conducted thermal infrared measurements of four volcanic lunar analogue samples; dunite (Twin Sisters -1 and -2), basalt (BIR-1) and rhyolite (RGM-1) under controlled ambient conditions (350 K, 1000 mbar, N2 atmosphere) [4]. The integration of PASCALE with FTIR allows for the acquisition of thermal emission spectra (as opposed to typical laboratory reflectance), offering a more representative analog of data collected by orbiting infrared instrumentation. Spectra were measured across ~6000 to 350 cm⁻¹ at a resolution of 4 cm⁻¹. Quality assurance and calibration procedures followed established protocols outlined in [6,7,8].  BT Estimations: To evaluate BT performance at LTM’s spectral resolution, each sample’s measured radiance was convolved with LTM’s filter response to simulate instrument-resolution radiance. The resulting spectra were converted to BT using the Planck function. Seven distinct methods were applied to the LTM-resolution BT data to determine the maximum BT values for each sample (Table 2). Emissivity was subsequently derived as the ratio between the observed LTM-resolution radiance and an ideal blackbody at the retrieved maximum BT for each method across all samples. The accuracy of the BT estimation methods was assessed by comparing the resulting emissivity spectra and maximum BT values to the full laboratory reference data (350K and full resolution emissivity). Additionally, a focused comparison with Diviner’s BT retrieval method was conducted to identify method-specific discrepancies and evaluate cross-instrument consistency.Table 2: BT estimation methods Results & Discussion: Six BT estimation methods were applied to laboratory emissivity spectra of four lunar analogue samples (dunite, basalt, and rhyolite), as shown in Figure 2. The associated standard errors (SE) for each method are reported in Table 3. Among the tested approaches, four methods (3rd degree polynomial, quadratic, spline and narrowband maximum) showed close agreement with high-resolution laboratory spectra (Figure 2). Temperature variations across compositions were minor, with low SE values (Table 3).  Since the spline fit did not significantly outperform the simpler polynomial or narrowband methods, lower complexity approaches are preferred for LTM temperature retrievals, with a maximum SE of 3.42%.In contrast, due to limited spectral sampling, the Diviner method underestimates surface temperatures by up to 19 K (SE max: 5.55%) in the dunite (TS-2) sample. Expanding this analysis to include a broader range of lithologies or impacted processed samples would help assess whether the Diviner approach (and potential other methods with sparse spectral sampling) introduce systematic shifts in the Christiansen Feature (CF) position or affect the spectral shape relative to more spectrally resolved techniques.  Table 3: BT estimations and associated SE of temperature for dunite (TS-1, TS-2), basalt (BIR-1) and rhyolite (RGM-1). Fig 2: Six BT methods are fitted to laboratory emissivity spectra of four lunar analogues. Conclusion:Comparisons between BT estimation methods indicate the 3rd-degree polynomial, quadratic, and narrowband maximum methods offer the best agreement with laboratory data (SE max: 3.42%). Although Diviner’s method tends to underestimate surface temperatures (up to 19 K), it still preserves spectral shape and wavelength range, supporting the reliability of compositional interpretations. Expanding the dataset to include a broader range of compositions could confirm whether different approaches result in systematic shifts in the Christiansen Feature across different lithologies. This work enhances the accuracy of remote compositional interpretation and supports future exploration on airless bodies.