Fig. 1: Inversion results.
From: Geophysical evidence for an enriched molten silicate layer above Mars’s core
Thermochemical evolution and present-day structure of Mars. One model among the best 50 is displayed for each inversion set. a–f, Without a BML (homogeneous mantle), with η0 = 6 × 1021 Pa s, E* = 300 kJ mol−1, V* = 3.8 cm3 mol−1. g–l, With a BML (heterogeneous mantle), with η0 = 5 × 1020 Pa s, E* = 110 kJ mol−1, V* = 4.4 cm3 mol−1. a,g, Evolution of crustal and lithospheric thicknesses (including the uppermost mantle thermal boundary layer (TBL)). b,h, Evolution of uppermost convective mantle (Tm) and core (Tc) temperatures. c,i, Present-day temperature profiles and mantle melting curves from ref. 48 accounting for the influence of iron in the BML3. d,j, Density profiles. e,k, Shear and compressional wave speed profiles. f,l, Raypaths for waves reflected at (blue) or diffracted along (red) deep mantle interfaces. Additional raypaths for other phases considered for the inversion are shown in grey. m,n, Close-up views of the region delineated in the vicinity of the BML in l, showing the P- and S-wave velocity structure (m) and raypath (n) of the P-diffracted wave reflected at the CMB (PbdiffPcP). In the homogeneous mantle, S-wave reflection occurs at the CMB, while in the heterogeneous mantle, it occurs above the CMB where velocity decreases abruptly due to the transition from a partially molten to a fully/essentially molten state in the BML (dotted curves). In the heterogeneous mantle, the P-diffracted phase (PbdiffPcP) travels in a molten silicate mantle with slower wave speeds compared with those in a solid mantle, significantly delaying its travel time. The PbdiffPcP phase results from multiple rays diffracted at the top of the fully molten BML before and/or after core reflection, which contribute to this seismic phase. The path displayed corresponds to one of these contributions, which is the reason why it is not symmetric. However, because the seismic model is spherically symmetric, the sum of the contributions will result in a symmetric path (Supplementary Fig. 4).
