Lunar asymmetry and interior dynamics

Kurzfassung

The lunar asymmetry is a very distinctive feature of the Moon, one that is reflected not only visually in the distribution of the darker mare regions but is also evident in other observational parameters such as topography, surface composition and gravity. Such asymmetry is at odds with the expected laterally homogeneous properties arising from the crystallization of a global magma ocean, and thus the origin of this asymmetry has been one of the most fundamental questions in lunar science. Here, we provide an overview of the observational data, discuss proposed scenarios for the origin of the asymmetry, and demonstrate what further implications the observed asymmetry may have for the Moon’s current internal structure and dynamics. Beyond that, we describe key future measurements (heat flux, tides, and seismic measurements) for further characterizing and elucidating the extent and origin of the Moon’s asymmetry. Furthermore, we argue that there is likely not just a single possible cause for the asymmetry, despite the fact that e.g. an asymmetry in crustal thickness - as is suspected on the Moon - has many causal relationships with other observable quantities, and thus an asymmetry in these is to be expected. Rather, it is the result of a superposition of several relevant (we speculate at least two) events: one during the crystallization of the magma ocean and at least one additional event thereafter.