The large and unusual orbital tilt of the Earth's moon has been finally explained. It has been estimated that the moon's orbit is inclined by at least 5 degrees vis-à-vis Earth's around the sun.
The theories on the tilt are all linked to the moon's formation. Early research suggested the newborn Earth was hit by a Mars-size rock called Theia, and the resulting debris led to the formation of the moon and caused far-reaching changes in the orbits of Earth.
Published in the journal Nature, the research paper, "Tidal Evolution of the Moon from a High-Obliquity High-Angular-Momentum Earth," has Matija Ćuk as lead author with Douglas Hamilton, Simon Lock and Sarah Stewart as the co-authors.
According to the study, the tilt might have been caused by a giant angled impact and the infant Earth got vaporized forming the moon.
Stewart says the giant impact that created the moon might have hit Earth at a highly slanted or oblique angle. That tilted Earth in such a way that its axis of spin slanted 70 degrees compared with the sun's axis of spin.
With the moon pulling away from Earth over the years, rates of rotation slowed too, and the moon later reached a point called the Laplace plane transition and escaped the influence of Earth.
After the moon crossed the Laplace plane, Earth set right its axis of spin to the current tilt of 23.5 degrees. That explains why the moon orbits Earth at a higher angle of 30 degrees, Stewart said.
Thanks to Earth's tilt, gravitational forces between Earth and the moon turned unequal at the poles and equator. That is why a lower inclination of the moon's orbit to the current 5 degrees exists.
On the legitimacy of the theory that early Earth was hit and caused the current tilt to the moon's orbit, Stewart said it is reasonably likely and rated the chances at 30 percent.
Faster Spinning Of Earth
According to scientists, in the high-energy impact that created the moon, most of Earth including the mantle region got vaporized. As a result, a dense vapor cloud was formed that was 500 times bigger than today's Earth. Later, much of the material fell back to Earth and the debris led to the formation of the moon.
The massive punch from the hit also made Earth spin very quickly with a day being completed in 2 to 3 hours.
"We already suspected that the Earth must have spun especially fast after the impact," Ćuk said.
However, as billions of years passed, the fierce gravitational interactions between Earth and the moon slowed, and Earth came to the current 24 hours to complete a day.