Four and a half billion years ago, the Earth’s surface was a hot mess, unfriendly to life. Long before its appearance, the temperature on the planet was scorching, and the air was toxic. In addition, at that time, the Sun was bombarding the Earth with strong emissions of radiation, attacking the planet with coronal mass ejections and a stream of charged particles (solar wind). Then the planet was uninhabitable. But perhaps the Earth had a “shield” nearby, which helped the planet preserve its atmosphere and, ultimately, not only develop life, but also suitable conditions for it. The latest NASA study, published in Science Advances, suggests the Moon was the shield.
“The Moon appears to represent a significant protective barrier from solar wind for Earth, which was critical to Earth’s ability to maintain its atmosphere during this time,” explains Jim Green, chief scientist at NASA and lead author of the new study. “We look forward to confirming our findings when NASA sends astronauts to the moon using the Artemis program, which will deliver critical samples of the Moon’s South Pole to Earth.”
According to leading theories, the Moon formed 4.5 billion years ago when a Mars-sized object called Theia crashed into proto-earth. Then our planet was less than 100 million years old. The debris of the collision formed the Moon, and the other remnants were reunited with the Earth. Due to the force of gravity, the presence of the Moon stabilized the Earth’s axis of rotation. At that time, the Earth was rotating much faster, one day only lasted 5 hours.
And in the early days, the Moon was much closer to Earth. Now it is moving away from the Earth at a speed of 3.81 cm per year. Four billion years ago, the Moon was three times closer to Earth than it is today – about 129,000 km, up from 383 km today.
Previously, scientists believed that the moon never had a long-term global magnetic field due to the small size of its core. However, it has long been known about the Earth’s magnetic field, which creates beautifully colored auroras in the Arctic and Antarctic. The movement of liquid (due to the heat left over from the formation of the Earth) iron and nickel deep inside the planet generates magnetic fields that form a protective bubble that surrounds it – the magnetosphere.
But thanks to studies of samples of the lunar surface from the Apollo missions, scientists have found that the moon once also had a magnetosphere. Evidence continues to accumulate after examining specimens that have been sealed for decades and recently analyzed using modern technology.
As on Earth, the heat from the formation of the moon could hold the iron inside, although not for as long due to its size.
“It’s like baking a cake: you take it out of the oven and it’s still cooling,” explains Green. “The more mass, the longer it takes to cool down.”
The new study simulates the behavior of the magnetic fields of the Earth and the Moon about 4 billion years ago. Scientists have created a computer model to look at the behavior of magnetic fields at two positions in their respective orbits.
The researchers stated that at a certain time, the Moon’s magnetosphere could serve as a barrier to harsh solar radiation falling on the Earth-Moon system. According to the model, the magnetospheres of the Moon and Earth were magnetically connected in the polar regions of each object. Important for the evolution of the Earth, the high-energy particles of the solar wind could not completely penetrate the bound magnetic field and separate the atmosphere.
Scientists have calculated that this common magnetic field situation, when the magnetospheres of the Earth and the Moon are connected, could have persisted from 4.1 to 3.5 billion years ago.
Over time, as the interior of the moon cooled down, our closest neighbor lost its magnetosphere, and eventually its atmosphere.
If our Moon played a role in protecting the Earth from harmful radiation at a critical early time, then similarly, other moons around Earth’s exoplanets in the galaxy can help preserve the atmosphere for their planets and even contribute to its habitability conditions, scientists say.