In-situ ionospheric observations near lunar south pole by the Langmuir Probe on Chandrayaan3 Lander

In-situ measurements of the near surface lunar plasma environment are made using the RAMBHA-LP (Radio Anatomy of the Moon Bound Hypersensitive ionosphere and Atmosphere -Langmuir Probe) payload onboard India’s Chandrayaan-3 Lander during lunar day time (24-08-2023 to 02-09-2023). These observations provide estimates of near surface ( 2 meters above the surface) lunar electron density and electron temperature from the south polar region, ‘for the first time'. The estimations reveal the daytime lunar plasma to have mean electron density (Ne) in the range of 380-600/cc and mean electron temperature (Te) in the range of 3000-8000 K. The critical roles of solar wind and the Earth’s magnetospheric particle flux in modulating the lunar dayside ionosphere outside and inside the Earth’s geomagnetic tail respectively are unraveled using RAMBHA-LP observations and Lunar Ionospheric Model (LIM) simulations. The study also highlights the role of molecular species in the genesis of lunar near surface plasma environment.