An examination of the evidence for and feasibility of a molten silicate basal layer in Mars’ mantle

One of the aims of the InSight mission was to seismically constrain the size and character of Mars’ core, however, seismology on Mars is challenging, involving the interpretation of low-amplitude signals with a relatively high noise level from small magnitude marsquakes on a single seismometer. Two recent papers propose a smaller core than previous studies that is overlain by a molten layer at the base of Mars’ mantle. Here we suggest that the seismic observations presented in support of this conclusion can be alternatively explained by scattering in the mantle, and that a basal layer is therefore not required by the data. Furthermore, we discuss several problems for the evolution and dynamics of Mars arising from the presence of the basal layer. We suggest that other possibilities should be considered, and that significant further investigation is required to determine the structure of Mars’ lowermost mantle and core. • It has recently been proposed that Mars’ mantle has a molten basal layer. • The seismic data giving evidence for this are critically re-examined. • Scattering – known to be prevalent on Mars - is shown to be a simpler explanation. • A basal layer is therefore not required to explain the seismic data. • A basal layer also raises questions about Mars’ evolution and dynamics.