The moon's orbit is tilted because of gravitational forces from large, nearby-passing rocks that crashed into the Earth billions of years ago, a new study revealed.

These giant rocks also added an overlay of metals onto the Earth, contributing about one percent to the mass of the planet, researchers said.

Scientists believe that when Theia, a space rock the size of Mars, struck the Earth more than 4.5 billion years ago, the moon emerged from the debris that came from the collision. The moon's orbit is currently tilted about five degrees as regards to the position of the planet, and previous studies explained that the moon's leaning should be 10 times smaller. This mystery is called the lunar inclination problem.

How The Moon's Orbit Became Tilted

Researchers of the new study simulated the moon moving around the orbital plane of the Earth. They simulated rocks with a total mass equivalent to 0.75 to 1.5 percent of the mass of the planet.

Before the huge rocks crashed into Earth, they usually passed by the planet within close proximity. These close passes may have brought them near enough to the planet or to the moon to gravitationally tug its orbit. It was highly likely that millions of years after the formation of the moon, these nearby-passing rocks could have caused the moon's orbit to become tilted, scientists said.

Planetary scientist Kaveh Pahlevan, the study's lead researcher, explained that what surprised them was the ease with which the orbital trajectory of the moon can by tilted by gravitational interactions.

"A surprisingly small amount of mass passing close by is enough to gravitationally nudge the Moon out of its original orbit," said Pahlevan.

The formation of the moon may have happened as the formation of the Earth ended, researchers said. If the lunar formation transpired much earlier, the orbit of the moon would have been destabilized. The moon could have collided with the Earth or escaped beyond the solar system.

Metals On The Earth's Outer Layer

Meanwhile, because the newborn Earth was extremely molten, scientists said that majority of the iron in the planet sunk to the core.

Metals such as iridium, platinum and gold have a high chemical affinity for iron, and when the iron went deep into the Earth's core, these elements should have sunk with it.

This is why scientists believe that the metals on the outer layer of the Earth were brought by huge collisions from many other gigantic rocks, all of which happened after the formation of the Earth's core.

The findings of this study are featured in the journal Nature.

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