The lunar environment is known to be characterized by complex interactions between plasma, the exosphere, dust, and the surface. However, our understanding of the environment is limited due to the lack of experimental evidence. Here, we propose a small, low-cost mission to characterize the dust and exosphere environment of the Moon. Named the Limb Pathfinder (LimPa), this is a proof-of-concept mission aimed toward understanding the coupling between plasma, dust, and tenuous neutral atmosphere. The LimPa mission was proposed to a call for the Small Mission to the Moon issued by European Space Agency in 2023. LimPa is designed to examine the dust exosphere above the lunar polar regions by using an utterly novel remote-sensing technique to measure the solar wind hydrogen atoms-the solar wind protons that are neutralized to hydrogen atoms. Its goals are (1) to detect for the first time the neutralized solar wind hydrogen produced by exospheric gas and levitated dust; (2) to measure the height profiles of the levitated dust and exospheric gas densities; and (3) to determine the emission mechanism of the horizon glow. Our baseline design of the LimPa mission is a 12U CubeSat. Three highly matured instruments are used: an energetic neutral atom camera, a proton sensor, and a camera system. The LimPa CubeSat is proposed to be inserted into a circular lunar polar orbit, with an altitude of 100 km as a baseline. The Sun-pointing attitude will allow measurements of neutralized solar wind that are produced by the exosphere and dust grains above the polar regions. The nominal lifetime is for 3 months as a pathfinder mission. The LimPa mission will open a new window to remote characterization of the lunar dust exosphere environment above the poles, and will demonstrate that this monitoring can be achieved with a simple and low-cost instrument system and spacecraft operation. The concept to be proven by the LimPa mission will enable long-term monitoring of the fragile dust exosphere environment, which substantially impacts on lunar exploration and will be significantly altered by human activities.

Solar wind precipitation on atmosphere-less bodies like the Moon generates backscattered and sputtered energetic neutral atoms (ENAs) from the surface. Since ENAs does not sense electromagnetic fields, ENAs can be assumed to retain the initial velocity if gravity effect can be ignored. This makes remote sensing of surface properties and near-surface plasma conditions possible from a spacecraft orbit. Lunar Neutrals Telescope (LNT) is an ENA instrument on the first Turkish Lunar Mission. LNT is tailored to answer several fundamental scientific questions. Three scientific objectives are set: (1) To search for volatile-rich areas on the surface including permanently shadowed regions, (2) to investigate the structure of mini- magnetosphere created by lunar magnetic anomalies and its response to the solar wind, and (3) to investigate the formation and maintenance processes of the lunar exosphere. We will present LNT scientific objectives as well as a brief description of the instrument.

We present the first direct measurement of neutral oxygen in the lunar exosphere, detected by the Chandrayaan-1 Energetic Neutral Analyzer (CENA). With the lunar surface consisting of about 60% of oxygen in number, the neutral oxygen detected in CENA's energy range (11eV-3.3keV) is attributed to have originated from the lunar surface, where it was released through solar wind ion sputtering. Fitting of CENA's mass spectra with calibration spectra from ground and in-flight data resulted in the detection of a robust oxygen signal, with a flux of 0.2 to 0.4 times the flux of backscattered hydrogen, depending on the solar wind helium content and particle velocity. For the two solar wind types observed, we derive subsolar surface oxygen atom densities of N-0= (1.1 0.3) 10(7)m(-3) and (1.4 0.4) 10(7)m(-3), respectively, which agree well with earlier model predictions and measured upper limits. From these surface densities, we derive column densities of N-C= (1.5 0.5) 10(13)m(-2)and (1.6 0.5) 10(13)m(-2). In addition, we identified for the first time a helium component. This helium is attributed to backscattering of solar wind helium (alpha particles) from the lunar surface as neutral energetic helium atoms, which has also been observed for the first time. This identification is supported by the characteristic energy of the measured helium atoms, which is roughly 4 times the energy of reflected solar wind hydrogen, and the correlation with solar wind helium content.