Abstract Details
| Name: Ashish Devaraj Affiliation: CHRIST (Deemed to be University) Bangalore Conference ID: ASI2025_283 Title : Observational Evidence Contrasting the Linear PSD Model: Non-Linear Correlations of Solar EUV/FUV Radiation with Lunar Sodium Authors and Co-Authors : Ashish Devaraj 1, Shyama Narendranath K. C. 2, Sreeja. S. Kartha 1, Menelaos Sarantos 3, Akhil Krishna R. 1, T. Sivarani 4, Nidhi Sabu 1,5, Blesson Mathew 1, P. Anbazhagan 4, G. Selvakumar 4 Abstract Type : Poster Abstract Category : Sun, Solar System, Exoplanets, and Astrobiology Abstract : Photon-stimulated desorption (PSD) is a non-thermal process where high-energy photons release surface-bound atoms, such as sodium, from planetary bodies like the Moon. To examine the link between solar Extreme Ultra-Violet (EUV) radiation above 8.8 eV and sodium release from the lunar surface through PSD, we use simultaneous measurements of EUV photon flux and Na optical spectral line flux from the lunar exosphere. Data were collected using the high-resolution (R$\sim$72000) Echelle Spectrograph on the 2.34-m Vainu Bappu Telescope during first-quarter lunar phases (January-March 2024), observing NaI D2 and D1 flux below $\sim$590 km. Simultaneous EUV and FUV data were obtained from the GOES-R Extreme Ultraviolet Sensor (EUVS), and NUV data from the Total and Spectral Solar Irradiance Sensor-1 (TSIS-1) on the ISS. We correlated the Na spectral line flux with EUV photon flux in six EUVS bands spanning 256-1405 $\AA$ (48.5-8.8 eV) and NUV data (2000-4000 $\AA$) from TSIS-1. Our results reveal a non-linear increase in lunar exospheric sodium with rising EUV and FUV fluxes between 8.8-48.5 eV, contrasting with previous linear PSD models. We confirm that EUV radiation above 10 eV contributes to sodium release via PSD, with wavelengths 256-304 $\AA$ playing a significant role. Additionally, we observe a positive correlation between NUV flux and sodium optical line flux, supporting NUV involvement in sodium release. The line-of-sight column density averages $5.71 \times 10^{9}$ atoms cm$^{-2}$, with Chamberlain temperatures averaging 6721 $\pm$ 127 K and scale heights of 1494 $\pm$ 28 km, consistent with non-thermal processes. Higher temperatures and sodium densities during solar activity suggest an enhanced Na release during solar flares. These findings indicate a need to revise the PSD model for photon energies above 8.8 eV and establish more precise constraints on the PSD cross-section in this range. |