By studying moon rocks, researchers at Rutgers University have discovered that the moon’s magnetic field lasted 1 billion to 2.5 billion years longer than once thought.
The findings could have important implications in regard to habitability on other moons and planets in space.
“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,” said Sonia Tikoo, an assistant professor in Rutgers’ Department of Earth and Planetary Sciences.
Without this shield, Earth would be hit with more radiation leading to more mutations and an unstable environment making it a much harsher place to live.
In their research, the team was able to successfully heat a lunar rock brought back to Earth during an Apollo space mission for the first time. This allowed researchers to retrieve accurate intensity for the lunar magnetic field since rocks can record magnetic fields to which they were exposed.
Tikoo used a rock magnetometer to analyze the lunar rock that measures the strength and direction of magnetic fields in rocks. Then researchers slowly demagnetized the rock to reveal its original magnetization and heated it to 1,436 degrees Fahrenheit in a controlled atmosphere chamber to keep the heat from altering the rock.
Results of the study led researchers to believe the moon’s magnetic field declined by about 90 percent from its high point 3.56 billion years ago or earlier when it was about the same strength as the Earth’s, about 50 microtesla.
The lunar rock, which is about 1 billion to 2.5 billion years old, recorded 5 microtelsa. Since the moon has no core-generated magnetic field today, scientists don’t know when it turned off.
“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,” Tikoo said. “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.”
When a planet’s magnetic field dies, ionizing particles from its sun can lead to the loss of its water over hundreds of millions of years. Mars once had lots of water but lost nearly all of it after its magnetic field died about 4 billion years ago.
“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,” Tikoo said. “Then the question becomes what size planets and moons should we be considering as possibly habitable worlds.”
The full research can be found in the journal Science Advances.