Chang'e-6 far-side rocks point to Earth-driven magma flows behind the Moon's two faces

Different rocks report on different layers, and the study uses that. The Chang'e-6 basalts carry chemical signatures of depleted mantle material, much like the low-Ti basalts Apollo astronauts returned ^[4]. Mg-suite rocks form when parts of the accumulated mantle partially melt and interact with crust, so their magnesium number (Mg#) indicates the mantle they came from ^[6]. Anorthosites speak to the crust ^[8].

In the mantle, the Mg# values of Chang'e-6 and Apollo Mg-suite samples are similar, and the researchers concluded that the cumulates under both sides share broadly similar chemistry ^[7]. In the crust, far-side anorthosites have higher peak Mg# than comparable Apollo samples ^[8]. That agrees with earlier remote observations ^[8]. Far-side Mg-suite rocks also contain extremely low concentrations of rare earth elements and have lower Th/Sm ratios ^[9]. The source text breaks off before the authors say what they read into that last ratio.

The mantle was the open question. Scientists had been uncertain whether the hemispheric contrasts seen at the surface and in the crust extend deep into the mantle ^[12]. If the cumulates are alike, the asymmetry lives in crust-level rocks, and a model has to produce a uniform interior under a lopsided shell ^[5].

The cause is a separate step. The team says its findings suggest that large-scale heat-driven circulation in the ancient magma ocean, after the Moon became tidally locked to Earth, produced the differences ^[14]. The Science China Press summary puts it as uneven heating from Earth's gravitational pull driving enormous flows of ancient magma ^[15]. Earlier proposals numbered four ^[13]: magma ocean circulation, a massive collision, tidal heating and uneven crust development, and none has won universal acceptance ^[11]. In our view the Nanjing account is closer to a combination of the circulation and tidal-heating ideas than a fifth entrant. The chemistry as described locates where the asymmetry sits more directly than it shows what drove it.

Two limits on the evidence. The comparison runs across missions, so hemisphere is entangled with where each spacecraft landed ^[2]. The release does not report sample counts, landing sites or a journal. The thing this doesn't tell you is whether the same data rule out the collision explanation, and the source does not say.