The Moon may have acted as a protective shield for a young Earth

Around 4 billion years ago, a massive object the size of Mars collided with a young, developing Earth.

The collision tossed vaporized particles from the Earth into space, which were then bound together through gravity to form the Moon.

This is just one theory of how the Moon formed. Since then, our planet and its only natural satellite have been inseparable since. A new study suggests that the Earth and Moon's relationship runs even deeper, and that the Moon may have shielded the Earth from losing all its atmosphere — allowing life to flourish on our planet.

The findings are detailed in a study published this week in the journal Science Advances.

When it first formed, the Moon was three times closer to Earth than it is today — some 80,000 miles away, For context, it is now 238,000 miles from Earth.

Lunar samples returned by astronauts during the Apollo missions revealed the Moon once had a magnetic field like Earth's, which acted as a shield from electrical charges.

In the new study, scientists simulated how the Earth's and the Moon's magnetic fields would have interacted some 4 billion years ago, when the pair were much closer to one another. What they found suggests the Moon was not merely Earth's close companion — it was our planet's protector.

“The Moon seems to have presented a substantial protective barrier against the solar wind for the Earth, which was critical to Earth’s ability to maintain its atmosphere during this time,” Jim Green, NASA’s chief scientist and lead author of the new study, said in a statement accompanying the research.

The magnetosphere of the Moon and Earth, the region of space that surrounds an object where charged particles are affected by that object's magnetic field, would have been magnetically connected at each of their polar regions.

As a result, the charged particles emitted by the Sun as solar wind would not have been able to penetrate the pair's shared magnetic field.

Without the Moon, Earth may not have been able to withstand the Sun's powerful radiation emissions, which constantly bombarded the young planet at the time. If these emissions had made it through the shield, it would have made it impossible for life to thrive on our planet.

Over time, however, the Moon slowly lost its magnetic field and its atmosphere.

Understanding the Moon's effect on the Earth's habitability helps scientists in their hunt for signs of life on other worlds. This study suggests an exoplanet's moon could affect the potential for life on that world.

The scientists behind this study plan to further validate their findings using data collected during NASA's upcoming Artemis mission to the Moon. One of the mission's goals is to return the first lunar samples from the Moon's South Pole, where it is believed that the Moon and Earth's magnetic field were most strongly connected.

“We look forward to following up on these findings when NASA sends astronauts to the Moon through the Artemis program," Green said.

"Significant samples from these permanently shadowed regions will be critical for us to be able to untangle this early evolution of the Earth’s volatiles, testing our model assumptions," he noted.

Abstract: Apollo lunar samples reveal that the Moon generated its own global magnetosphere, lasting from ~4.25 to ~2.5 billion years (Ga) ago. At peak lunar magnetic intensity (4 Ga ago), the Moon was volcanically active, likely generating a very tenuous atmosphere, and, it is believed, was at a geocentric distance of ~18 Earth radii (R_E). Solar storms strip a planet’s atmosphere over time, and only a strong magnetosphere would be able to provide maximum protection. We present simplified magnetic dipole field modeling confined within a paraboloidal-shaped magnetopause to show how the expected Earth-Moon coupled magnetospheres provide a substantial buffer from the expected intense solar wind, reducing Earth’s atmospheric loss to space.