Core–mantle boundary Core–mantle boundary The core–mantle boundary (CMB in the parlance of solid earth geophysicists) of the Earth lies between the planet's silicate mantle and its liquid iron-nickel outer core. This boundary is located at approximately 2891 km (1796 mi) depth beneath the Earth's surface. The boundary is observed via the discontinuity in seismic wave velocities at that depth due to the differences between the acoustic impedances of the solid mantle and the molten outer core. P-wave velocities are much slower in the outer core than in the deep mantle while S-waves do not exist at all in the liquid portion of
ITS launch vehicle "evolved quite a bit" since the November 2016 articulation of the very large "ITS launch vehicle." A key driver of the new architecture is to make the new system useful for substantial Earth-orbit and cislunar launches so that the new system might pay for itself, in part, through commercial spaceflight activities in the near-Earth space zone. In September 2017, the new smaller design was revealed to be the diameter launch vehicle, referred to by its "code name" BFR, with similar core vehicle structure (carbon fiber), engines (Raptor), and Mars mission architecture; but explicitly aimed at superseding and replacing the entire