In December, scientists discovered that lunar material brought to Earth-the first new Moon rocks discovered since the 1970s-was approximately a billion years younger than previously dated samples. This suggests that liquid magma existed on the Moon billions of years earlier than previously thought, raising issues about how the Moon's rock melted.

"All our experience tells us that the moon should be cold and dead 2 billion years ago. But it is not, and the question is, 'Why?'" Alexander Nemchin, author of the analysis published Thursday in the journal Science, said.

The Chang'e 5 mission returned 3.81 pounds (1.73 kilograms) of moon rock to scientists on Earth from a location known as Oceanus Procellarum. Since then, scientists who have gained access to the valuable material have embarked on a series of tests to learn more about the rocks and the secrets of the solar system they may contain.

The age data they've compiled is remarkable because it shows that volcanism on the Moon occurred long after one would anticipate such a small body to cool down and cease active.

Theorists will now consider fresh possibilities for what kind of heat source could have kept the late-stage behavior going.

Because the Chang'e 5 samples don't contain many of the chemical elements associated with this effect, it doesn't appear to have been caused by concentrated radioactive decay. Or, due to the conditions of its formation, rock could have melted early in the Moon's history, when it was much hotter than it is now.

Impacts on the Moon and tidal heating are another possible explanation. Earth pulls on the Moon in the same way that the Moon pulls on the Earth, generating tides. However, because the Moon lacks plate tectonics, all of the yanking and scrunching generates heat via friction.

Fortunately, more data is on the way. The Chang'e 5 samples are a taster for NASA's next Artemis mission, which will deliver much more rock samples to Earth for analysis.

Because the Moon serves as a standard for dating other planetary surfaces, the more information these lunar rocks can provide, the better we will be able to determine the ages of other worlds. The Chang'e 5 rocks are only the start of a resurgence in lunar exploration.