Overview

• Laboratory measurements estimate the far-side basalt formed at about 1,100°C, roughly 100°C cooler than comparable near-side rocks.
• The team dated the fragments to about 2.8 billion years using ion-probe lead isotopes and mapped mineral chemistry with electron probes.
• Researchers say the cooler mantle likely reflects a scarcity of uranium, thorium and potassium that generate heat through radioactive decay.
• Hypotheses for the uneven element distribution include a giant impact, an early collision with a smaller moon, or tidal effects from Earth.
• Findings come from the first returned samples from the lunar far side via China’s Chang’e‑6 mission, though present-day mantle temperatures remain undetermined.