The Role of Self-Heating and Roughness in Micro Cold Trap Stability: Implications for Lunar Poles

Using the Moon as a case study, we explore the effects of surface roughness at a small scale on the temperature of airless planetary bodies. Roughness can significantly influence temperature through a phenomenon known as ”self-heating,” in which indirect light plays a crucial role. Solar radiation can be locally reflected and scattered, causing this indirect light to reach areas of the surface that are typically not directly illuminated. This indirect contribution becomes particularly important on very rough surfaces (where self-heating occurs on at millimeter scale) or in concave geometries, such as deep craters (where self-heating occurs on a meter or tenth of meters scale). Indirect light can locally increase the temperature by several degrees, affecting the the stability of likely ices. Our numerical model considers both vertical and lateral heat exchange. We analyze different rough surfaces representing ideal lunar polar sites, providing surface temperature maps, highlighting the contribution of self-heating and estimating the lifetime of potential volatiles on these surfaces. Moreover, this work could offer the thermophysical conditions that can be integrated in a Lagrangian code (such as a smoothed-particle-hydrodynamics code) to characterize the volatile emission and the formation of a transient exosphere. Our results suggest that in some areas, even if the self heating can contribute to the surface temperature, water ice can remain stable in small cold traps that are only fractions of a meter in size.