Shared Earth-Moon Magnetosphere Protected Their Atmospheres From Young Sun's Intense Wind, Study Says

How did the moon help the Earth eventually become habitable? A team of researchers found that the Earth and moon once shared a magnetosphere that protected both of them.

Scientists once believed that the moon never had a magnetic field but studies conducted by the Apollo astronauts revealed that our satellite indeed has a magnetic field, albeit a 1000 times weaker than the Earth's. This suggested that the moon once had a more substantial magnetic field that possibly lasted for several 100 million years.

What did the moon's past magnetic field mean to the Earth?

In a new study published in the journal Science Advances, a team of researchers simulated how the moon's past magnetic field may have behaved and affected the Earth billions of years ago. They found that the Earth and moon's magnetic fields were actually connected in the polar regions.

At the time, the sun was much younger and much more active in bombarding the Earth with charged particles and radiation. But the researchers found that the coupled Earth-moon magnetosphere prevented these potentially harmful particles from completely penetrating and stripping away their atmospheres. They wrote that the moon's magnetosphere would have taken "the brunt of the solar wind, no matter how intense."

"The results of our magnetic field topological modeling demonstrate a critical and previously unrecognized condition: that Earth-Moon coupled magnetospheres work together to protect the early atmospheres of both Earth and the Moon," the researchers wrote.

Because of this protection, the Earth retained its atmosphere and eventually went on to develop habitable conditions and, eventually, life. The moon eventually lost its magnetosphere, without the protection of which it also lost its atmosphere.

Today, the Earth's magnetic field is rather like a protective shield that deflects and traps most of the charged particles from the sun, thereby shielding the surface from harmful ultraviolet radiation.

What's interesting is that this is not the only way the moon significantly affected the Earth's history.

The Earth was once spinning much faster, completing a day in just five hours. But because of the moon, which at the time was much closer to the Earth than today, the Earth's spin axis stabilized, NASA said in a news release.

"Understanding the history of the Moon's magnetic field helps us understand not only possible early atmospheres, but how the lunar interior evolved," study co-author and NASA deputy chief scientist David Draper said in the news release. "It tells us about what the Moon's core could have been like -- probably a combination of both liquid and solid metal at some point in its history -- and that is a very important piece of the puzzle for how the Moon works on the inside."