China’s moon mission found something interesting.

Reuters reports that the Chinese moon mission brought back rock samples that were about a billion years younger than expected – meaning the molten early moon cooled much slower than we thought:

Samples brought back from U.S. and Soviet missions were more than 2.9 billion years old. The samples acquired on China’s Chang’e-5 mission late last year – around 1.96 billion years old – suggests volcanic activity persisted longer than previously expected.

“The Oceanus Procellarum region of the Moon is characterised by high concentrations of potassium, thorium, and uranium, elements that generate heat through long-lived radioactive decay and may have sustained prolonged magmatic activity on the near side of the Moon,” wrote the article’s authors, including Chinese researchers.

The article said the heat source for the magmatic activity might also be due to so-called “tidal heating”, or heat generated by the gravitational tug and pull of the Earth.