Peaks of Eternal Light on the Lunar South Pole: How They Were Found and What They Look Like

Abstract

This paper summarizes the search for the Peaks of Eternal Light (PELs) on the lunar South Pole. Already predicted in the 19 century, the question of existence of such peaks has revived after the Clementine and Lunar Prospector missions and detailed ground based radar imagery. These peaks can be considered primary targets for future robotic or manned missions. For the first time now, a detailed analysis has been made of the existence, whereabouts and characteristics of these peaks. Also tools have been developed to analyse the surface and slopes of the polar areas at pixel-level based on orbital imagery. Mission planners of the arising multitude of (commercial) lunar or Mercury missions can use this information and these tools to derive engineering implications. Why go to a Peak of Eternal Light? Fig. 1 explains how on the lunar poles both Sun and Earth appear only very low above the horizon, a characteristic that is only shared in our solar system by Mercury. Due to local topography (craters and depressions) this geometric condition creates regions of permanent shadow. Mountain tops sticking out of the icy shadows close to the pole will be lit by a Sun moving around low and close to the local horizon, and can be lit for significantly longer than the typical 14 days valid for the remainder of the lunar surface. Such a Peak of Eternal Light is expected to have some properties that make it particularly attractive for a future lunar landing: