Temporal Variations of ⁴⁰Ar and Radon Density Distributions in the Lunar Exosphere from Transient Events

Ian-Lin Lai^1*, Yi-Hsin Chang², Wing-Huen Ip¹

¹Graduate Institute of Astronomy, National Central University, Taoyuan City, Taiwan
²Department of Electrical Engineering, National Taiwan University, Taipei City, Taiwan

* Presenter:Ian-Lin Lai, email:ianlai@gm.astro.ncu.edu.tw

Moonquakes play a pivotal role in the liberation of noble gases, notably ⁴⁰Ar and Radon (²²²Rn) which is the decay product of ²³⁵U, from the moon's interior into its tenuous, surface-bound exosphere. The random-walk trajectories of these gas atoms are ballistic, characterized by much more frequent interactions with the lunar surface than with other gas particles. The details of the gas-surface interaction depend on the lunar surface temperature distribution and various photolytic and physico-chemical reactions, many of which are still under discussion. Following previous treatments guided by the measurement data from the Apollo/LACE experiment and the LADEE observations of the LDEX mission, we constructed time-dependent models of the ⁴⁰Ar and ²²²Rn density distributions immediately after a transient outgassing event. Our theoretical work is to prepare for in-situ monitoring of these rare gases and moonquakes by Moon-based instruments in the near future.

Keywords: planetary science, moon