New research suggests the magnetic field of the Moon lasted at least 1 billion years longer than previously thought, a finding that is significant for the habitability of exoplanets and exomoons. The lunar dynamo was previously thought to have lasted between 4.25 and 3.56 billion years ago, but this latest revision suggests that the magnetic field endurance might be related to a more complex source.

The analysis, published in Science Advances, was conducted on glassy lunar soil samples collected by the Apollo 15 mission. Within these lunar rocks, there are little shards of basalt, which give an accurate account of our satellite's magnetic history. The rock was estimated to have formed between 1 to 2.5 billion years ago.

"We didn't think that small planetary bodies could generate magnetic fields for a very long time because they have smaller cores that would cool quickly and crystallize early in their lifetimes," lead author Professor Sonia Tikoo, from Rutgers University, said in a statement. "Because the rate of crystallization depends on the core composition, our finding may challenge what we think the lunar core is made of. It's mostly made of iron, but something must be mixed in with it: sulfur, carbon or another element."

The magnetic field of the moon when those rocks formed was 5 microtesla smaller than what we currently experience on Earth, where the magnetic field varies between 25 and 65 microtesla.

"The Earth's magnetic field is a shield that protects us from dangerous solar wind particles and ionizing radiation, so magnetic fields play a key role in the habitability of planets and, possibly, moons," Professor Tikoo added. "Without this shield, we'd have more radiation, we'd have lots of mutations and who knows how life would respond in an unstable environment like that. It would be a harsher place to survive in."

Stellar winds and storms can severely affect a planet. Mars lost its atmosphere due to its lack of a magnetic field. Stars too active, like Proxima b, would be a challenge for our planet as well, so life-hosting bodies seem to require a strong magnetic field.

"Whenever we look at exoplanets or the moons of exoplanets that could be in the habitable zone, we can consider the magnetic field as an important player in habitability," she said. "Then the question becomes what size planets and moons should we be considering as possibly habitable worlds."

The study reminds us that there’s a lot more we need to learn about the Moon, even if we are looking at distant worlds.