TP11
This session invites oral and poster contributions across this broad area of the lunar environment. Key themes include
- Innovative science: Scientific outcomes using a range of methods, including data analysis, numerical simulation, lab experiments, instrumentation, future missions, and a combination of these.
- Pre-contamination characterization: What is needed to characterize the pristine state that is a critical benchmark for evaluating the impact of human activity.
- Interdisciplinary insights: Revealing mysteries of the coupling between different domains of the Moon and the space environment.
This session aims to gain insight into the complex coupling that shapes the lunar space environment, examine the implications for future lunar science, exploration, and human activities, engage with diverse scientists from various disciplines to share cutting-edge knowledge, and spark new ideas about science.
Session assets
The Negative Ions at the Lunar Surface (NILS) instrument [1] is the first instrument to measure negative ions directly on the lunar surface. Carried onboard the Chang’e-6 mission to the lunar far-side (South Pole-Aitken basin) in June 2024, the instrument produced 346 minutes of data. The instrument uses an electrostatic elevation scanning system and energy analyzer to measure the direction- and energy-resolved negative ion flux. The instrument field-of-view spans from the surface to space in 16 linearly-spaced angular steps. The instrument response, integrated over the 8 steps viewing the surface, is shown in Fig. 1 alongside the scattering function for energetic neutral hydrogen atoms (ENAs) previously derived from orbital observations [2].
Figure 1: Hydrogen ENA scattering function from Schaufelberger et al., 2011 along with the projected summed NILS response function.
NILS data provide direct constraints—at the emission source—on the energy and angular distributions of scattered and sputtered negative hydrogen ions. A detailed mathematical model of the instrument is used within a Bayesian inference framework to retrieve the scattering and sputtering functions. Finally, these NILS-derived functions are compared with orbital measurements of scattered solar wind protons and hydrogen ENAs.
[1] Canu-Blot, R., Wieser, M., Kérényi, M. et al. The Negative Ions at the Lunar Surface (NILS) Instrument on the Chang’E-6 Mission. Space Sci Rev 221, 38 (2025). https://doi.org/10.1007/s11214-025-01162-w
[2] A. Schaufelberger et al., “Scattering function for energetic neutral hydrogen atoms off the lunar surface,” Geophysical Research Letters, vol. 38, Art. no. 22, Nov. 2011.
How to cite: Canu-Blot, R., Wieser, M., Barabash, S., Stenberg Wieser, G., Kérényi, M., Wang, X.-D., Melville, N., and Zhang, A.: Scattering and Sputtering of Negative Hydrogen Ions from the Lunar Surface: Inference from NILS Observations on Chang’e-6, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-714, https://doi.org/10.5194/epsc-dps2025-714, 2025.
Solar wind precipitation on atmosphere-less bodies like the Moon generates backscattered and sputtered energetic neutral atoms (ENAs) from the surface and near-surface environment. Since ENAs does not sense electromagnetic fields, ENAs can be assumed to retain the initial velocity if gravity effect can be ignored. This makes global remote sensing of surface properties and near-surface environment possible from an orbiting spacecraft. Lunar Neutrals Telescope (LNT) is an ENA instrument onboard the first Turkish Lunar Mission AYAP-1 [1], which will be launched in early 2027. The LNT is designed to measure ENAs generated at the Moon surface from the orbit around the Moon and make a global map of plasma precipitation onto the Moon surface. There are three major scientific objectives for LNT observations: (A) To investigate the structure (shape) of mini-magnetosphere created by lunar magnetic anomalies and its response to the solar wind, (B) to search for volatile-rich areas on the Moon’s surface with the special focus on permanently shadowed regions, and (C) to investigate the formation and maintenance processes of the lunar exosphere.
The Design of the LNT, as shown in Figure 1, is based on the successful predecessor CENA/SARA sensor on Chandrayaan-1 [2] and is updated to achieve unprecedentedly high angular resolution (∼7° × 7°), which is approximately factor of 7 higher than the predecessor. Owing to its high angular resolution, the expected spatial resolution at the Lunar surface is ~12 km, which is small enough to resolve the fine structure of the mini-magnetosphere and properties of the permanently shadowed regions. The predicted performance of LNT is shown in the Table I. Energy and mass resolution of LNT also allows us to discriminate the process of plasma interaction with the surface (i.e. backscattered or sputtered), from which valuable information of surface properties can be derived.
We will present the predicted performance of LNT with the current status of development and discuss the expected science.
References:
[1] B. Yağlioğlu, et al. (2023), "The First Turkish Lunar Mission Part 1: Programmatic, Mission and System Aspects," 2023 10th International Conference on Recent Advances in Air and Space Technologies (RAST), Istanbul, Turkiye, 2023, pp. 1-6, doi: 10.1109/RAST57548.2023.10197907.
[2] M. Wieser et al. (2010), First observation of a mini-magnetosphere above a lunar magnetic anomaly using energetic neutral atoms, Geophys. Res. Lett., 37, L05103, doi:10.1029/2009GL041721.
How to cite: Shimoyama, M., Karlsson, S., Barabash, S., Futaana, Y., Wieser, M., Maynadié, T., Yağlıoğlu, B., Karagözoğlu, B., Öztürk, F., Nur ÇALIŞKAN, S., and Altay, Z.: Study of plasma interaction with Lunar surface environment: Science cases with Lunar Neutrals Telescope on Turkish Lunar Mission AYAP-1, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1325, https://doi.org/10.5194/epsc-dps2025-1325, 2025.
Introduction
The lunar dust environment in the exosphere, coupled with the other weather environments — plasma, electromagnetic field, and the surface regolith — is a highly dynamic system in nature. Particularly, since the discovery of the horizon glow in the 60s and 70s, scientists (and astronauts) have discussed the source of the emission. A potential, and widely accepted, hypothesis is the levitation of lunar dust in the near-terminator exosphere. However, it is still controversial due to the lack of experimental evidence. Recent measurements, particularly a dedicated in situ dust instrument on the LADEE spacecraft, did not find such dust components (Horanyi et al., 2015), raising questions about the levitated dust hypothesis.
Here, we propose a new, complementary technique of measurements using recently established energetic neutral atom imaging. The technique, named "Limb Sounding", can offer the exospheric density profile and levitated dust composition in the terminator region in a remote sensing manner (Futaana et al., 2024). In this presentation, we outline the technique, introduce its theory, and discuss its feasibility. We will also depict a simple system implementation as a pathfinder mission.
Outline of limb sounding
Figure 1 shows two main processes occurring in the dusty exosphere. The charge exchange with exospheric atoms neutralizes the solar wind (panel 1) and collision with a dust grain (panel 2). Depending on the size of the grain, the impinging solar wind proton is neutralized and decelerated. In both cases, the neutralized solar wind (also called energetic neutral atoms, ENAs) can reach the spacecraft that will be measured during the ingress to or egress from the lunar shadow. This geometry is required since the dusty exosphere is between the Sun and the spacecraft, and thus, the solar wind protons pass through the exosphere. Since a part of the solar wind will lose its charge states and be converted to energetic neutral atoms (ENAs) by several mechanisms in the dusty exosphere, the ENAs contain information about the dusty exosphere.
ENAs produced by exospheric gas: ENAs produced by the lunar exospheric neutrals were studied by Futaana et al. (2008). They conducted a forward model using an ideal exosphere and claimed that the ENA flux is high enough to be measured by an established ENA instrument. Theoretically, the flux is proportional to the exospheric density and the path length of the solar wind in the exosphere. Thus, the measured ENA flux contains the information of the exospheric density and spatial distribution (scale height). By time series measurements using the moving spacecraft, various paths of the measurements within an ingress (and egress) path can be measured.
ENAs produced by dust grains: Collision with dust grains is the other source of ENA production. Collier et al. (2009) established a theory of the dust-originated ENA production and demonstrated that the flux is measurable if the solar wind speed is high enough. The detection also depends on the dust grain size distribution. Here, we extended their theory to consider the energy loss and angular spread. This extension allows us to simulate the expected energy and directional distribution and their time series. This will further enable us to assess the feasibility of retrieving the dust grain size distribution and its height profile.
These two processes can be distinguished by measuring the energy of the hydrogen: The charge exchange does not alter the energy, but the dust grain penetration will decelerate the solar wind proton during the neutralization process.
Summary
In this presentation, we will outline the limb sounding technique, highlighting its theoretical feasibility. Particularly, their angular and energy distributions will be discussed. We further describe an example system to demonstrate the technique using a CubeSat as a pathfinder. With a relatively simple measurement system, the limb sounding technique can provide an opportunity to investigate the dynamic lunar dusty exosphere. Once it is validated, the measurement principle will potentially provide a long-term monitoring system of the lunar dusty exosphere, possibly contaminated by human activities in the coming decades.
Figure 1: Illustration of the Limb Sounding technique. (Top) A production mechanism of energetic neutral atoms (ENAs) by exospheric gas via the charge exchange mechanism. (Bottom) Another production mechanism of ENAs, i.e., the solar wind penetrating through dust grains in the exosphere.
How to cite: Futaana, Y., Gergacz, M., Kapitein, D., and Gustafsson, A.: Limb Sounding: A new remote sensing technique for lunar dusty exosphere monitoring, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-401, https://doi.org/10.5194/epsc-dps2025-401, 2025.
The Moon’s surface thermal environment is extreme compared to other planetary bodies in the solar system, with temperatures ranging between 400 K at the subsolar point and lower than 40 K in permanently shadowed regions around the poles (Paige et al. 2010). The surface temperature of the Moon also represents a fundamental boundary condition that governs the thermal state of the Moon’s regolith, the interior, and the behaviour of near-surface volatiles. The regolith is the layer of unconsolidated material covering the lunar surface, created by impacts and space weathering. The lunar environment is known to be characterized by interactions between the space plasma and the dusty surface, leading to a complex exosphere. Knowing more about the current state of the lunar regolith can give us insight into the geological history of the moon.
In contrast to in-situ measurements or returned samples, remote sensing measurements can be used to constrain surface properties on a global scale. NASA’s Lunar Reconnaissance Orbiter (LRO) was the first spacecraft to create a global 3D map of the lunar surface. During the 15+ years of operation of LRO, the Diviner Lunar Radiometer Experiment (Diviner) has measured the brightness temperature of the lunar surface in 9 wavelength channels ranging from 0.35 µm to 400 µm (Paige et al. 2010) with a spatial resolution of approximately 250 meters per pixel. With the help of thermal models, the Diviner measurements were used to derive global properties of the lunar regolith (Hayne et al. 2017). Based on the latter work, Bürger et al. (2024) developed a thermal model of the lunar regolith using microphysical parameters, such as the regolith grain size and stratification. However, their best-fit results to Diviner nighttime measurements were non-unique.
On the contrary to the diurnal cycle which spans roughly 29.5 Earth days, lunar eclipses (solar eclipses as seen from the lunar surface) provide cooling curves of the regolith on a much smaller timescale of roughly 4 Earth hours. As a consequence, eclipse cooling occurs only within a thin layer corresponding to the much shallower thermal skin depth < 1 cm (compared to ~10 cm for the diurnal cycle). Lunar eclipse events lead to a significant cooling of the lunar surface by ΔT ≈ 200 K, due to the lack of a lunar atmosphere. Therefore, eclipse events offer a unique opportunity to constrain the physical properties of the uppermost regolith layer, the interaction zone between the lunar space environment and the lunar surface.
We present a refinement of the thermal model of Bürger et al. (2024) by combining Diviner daytime, nighttime, and eclipse measurements to resolve the degeneracy of the solution space and give best-fit estimates for microphysical properties of the lunar regolith such as regolith grain size and stratification on a global scale. To capture the precise timing and geometry of each lunar eclipse we improve the upper boundary condition of the thermal model by using the SPICE toolkit. We filter for locations with a low rock abundance below the average of 0.4% (Bandfield et al. 2011) and small local slopes below 5 degrees, describing default regolith properties and avoiding offsets of the lunar local time. We analyse lunar maria and highlands independently and investigate a latitudinal trend of the derived regolith properties. A comparison with in-situ measurements conducted by the Apollo mission is made to confirm the results.
Figure 1: Comparison of the thermal model with the Diviner data for a location in the maria near the equator. The top panel shows the available Diviner measurements for this location between 2009-12-01 and 2024-06-01 on top of their respective simulated diurnal curves. Nighttime data are marked with triangles, daytime data with asterisks. The eclipse event on the morning side is marked with a circle and shown in the cutout in the top right corner. The temperature drops by ~200 K for a short duration and then rises quickly to continue the ascending curve of the morning side. A drop in temperature without a measurement means that the location was not in the field of view of Diviner during the eclipse, instead it is part of the diurnal curve of another data point. The bottom panel shows the difference between model and data with χ2 = 1.6 K.
References:
Paige et al. (2010), Space Sci. Rev., 150(1-4).
Bandfield et al. (2011), JGR, 116(12).
Hayne et al. (2017), JGR, 122(12).
Bürger et al. (2024), JGR, 129(3).
How to cite: Langermann, L., Bürger, J., Hayne, P. O., Delbo, M., and Blum, J.: Refining a Thermophysical Model of the Lunar Surface using Eclipses, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1060, https://doi.org/10.5194/epsc-dps2025-1060, 2025.