What the Moon Rocks Were Hiding

What the Moon Rocks Were Hiding By Mark Thompson - March 02, 2026 09:25 AM UTC | Planetary Science When the Apollo astronauts returned from the Moon, they brought back something more valuable than any treasure, 382 kilograms of Moon rock that would keep scientists busy for generations. For decades those samples have been scrutinised, measured, and debated and, for decades one question has refused to be satisfactorily answered… Did the Moon once have a powerful magnetic field or was it always magnetically feeble? On one side, scientists pointed to the Apollo samples themselves, many of which are strongly magnetised, suggesting the early Moon had a magnetic field comparable to or even exceeding Earth's. On the other side, theorists argued this was impossible. The Moon's core is tiny, barely a seventh of the Moon's total radius and too small to have generated a powerful dynamo. Both sides seem to have had evidence. The Apollo astronauts bought back 382 kg of Moon rock. The crew of Apollo 11 are pictured here from left to right, Neil A. Armstrong, commander; Michael Collins, command module pilot; and Edwin E. Aldrin Jr., lunar module pilot (Credit : NASA) Now researchers at the University of Oxford have cracked it and the resolution is one of those satisfying moments where a complicated mystery turns out to have a somewhat more simple explanation. Analysing the chemical makeup of a type of volcanic rock known as Mare basalts, the dark flat plains that give the Moon its familiar patchy appearance, the Oxford team found a striking pattern. Every lunar sample that had recorded a strong magnetic field also contained large amounts of titanium. And every sample with less than six percent titanium by weight was associated with a weak magnetic field. The correlation was clean and consistent across the entire dataset. What this tells us is that the Moon's magnetic history was not the steady, sustained configuration that decades of Apollo analysis had implied. Instead, for the va...