The moon once had a magnetic field stronger than that of the Earth, scientists say, but what made it work and what made it stop remains a mystery, according to Space.com.
The moon currently does not have a magnetic field, but moon rocks collected during the Apollo missions suggest that billions of years ago, the man-in-the-moon had a magnetic heart.
The moon might have powered its magnetic field like Earth does now, or cosmic impacts could have heated plasma which caused short bursts of magnetic forces (magnetizing the rocks), Space.com reported.
"We think planets generate magnetic fields by moving electrically conducting fluids inside them," said Benjamin Weiss, a planetary scientist at MIT. "The defining question of lunar science for more than four decades, even before the Apollo missions, is to what extent is the moon an unmelted primordial body like many asteroids, as opposed to a melted evolved body with a multilayered structure, which can have a metallic core with a magnetic field."
"The moon is intermediate between a planet and a small body like an asteroid, so establishing whether the moon had an ancient dynamo could help show that it was a highly evolved body differentiated into layers like Earth," Weiss told Space.com. "This would tell you about the origin of the moon - some models say the moon started off cold and unmelted, while others suggest it was created from a giant impact and predict it should have been hot."
Scans of lunar rocks show the lunar magnetic field probably occurred over 4 billion years ago, 1 billion years after the formation of the moon.
"It's hard to understand how the moon's magnetic field could be as strong as it seemed given how the moon has a very small core," Weiss said.
"The moon's core is maybe one-fifth to one-seventh the radius of the moon, while Earth's core is maybe one-half the planetary radius. This means the surface of the moon is much farther away from its core than you see with Earth. Since magnetic fields fall rapidly in strength with distance, it's hard to understand how the moon could have had a magnetic field that was that strong all the way to its surface."
