Complementary analyses further support a molten Basal Mantle Layer on Mars: A reply to Russell et al. (2026)

Seismic data offer a unique window into planetary interiors. Here, following a note from Russell et al. (2026), we provide further analysis to solidify our identification of a seismic phase detected by the InSight mission as one which interacts with a basal mantle layer (BML) on Mars (Samuel et al., 2023a). We show that other mantle discontinuities are unlikely to produce this seismic signal. We clarify how our proposed layered structure is compatible with other available geophysical observations and geodynamical constraints, and can be used to make inferences about Martian evolution. • InSight seismic data reveal P-wave phases interacting with a molten basal mantle layer on Mars. • Polarization and sensitivity kernels confirm CMB-interacting P-wave arrivals in event S1000a. • Mid-mantle reflections and mantle scattering cannot explain the observed seismic phases. • Basal mantle layer models remain consistent with Mars’s geodetic and lithospheric constraints. • A molten basal mantle layer is compatible with Mars’s thermal evolution and ancient dynamo.