The moon may be millions of years younger than we thought

13 Jul 2020

Image: © elen31/

New research has been able to determine how long it took a magma ocean on the moon to cool, possibly revealing when Earth’s satellite was formed.

While our understanding of how the moon formed has been agreed upon by large parts of the scientific community, when it was formed remains a more open question. Now, researchers from the German aerospace centre DLR and the University of Münster believe they have found evidence that suggests a new date of birth.

Writing in Science Advances, the researchers used a new numerical model to reconstruct the time at which a Mars-sized protoplanet dubbed Theia collided with the infant Earth and released the material that would become the moon.

Previous assumptions have given the moon an age of 4.51bn years, but this new modelling has pushed the timeline forward to suggest it is actually 85m years younger, with a 25m year margin of error.

At this time, the ring of dust that was left after such a cosmic collision formed the moon, potentially in as little as a few thousand years. During this violent impact, a several-thousand-kilometre-deep magma ocean formed on Earth. A magma ocean was also formed on the moon that was somewhat shallower at more than 1,000km in depth.

Cooling a magma ocean

This magma ocean quickly began to solidify and formed a crust of floating, lightweight crystals at the surface of the moon and the cold vacuum of space. Until now, scientists were unable to determine how long it took for the magma ocean to crystallise completely, which is why they could not conclude when the moon originally formed.

The new modelling estimated that it took the moon’s magma ocean almost 200m years to completely solidify into mantle rock and is one of the first comprehensive studies to do so.

To then determine the age of the moon, the scientists had to calculate how the composition of the magnesium- and iron-rich silicate minerals that formed during the solidification of the magma ocean changed over time. This revealed a drastic change in the composition of the remaining magma ocean during solidification.

“By comparing the measured composition of the moon’s rocks with the predicted composition of the magma ocean from our model, we were able to trace the evolution of the ocean back to its starting point, the time at which the moon was formed,” said Sabrina Schwinger, co-author of the study.

Colm Gorey was a senior journalist with Silicon Republic