When we look up at the night sky and see the moon, we see what we believe is a perfectly round object. However, scientists recently discovered that the moon is not spherical, but shaped more like a lemon.
A new study suggests that this shape is due to the moon's spinning when it was younger, along with the tidal pull of the Earth, creating a specific gravitational effect that stretched out its core.
In their study, researchers used a laser altimeter to map out the surface of the moon with extraordinary detail. This allowed them to figure out the moon's topography, which then led them to the discovery that the Moon is lemon-shaped. Getting accurate measurements was problematic in previous studies because of the moon's rocky exterior.
Once researchers discovered the moon's shape, they were then tasked with discovering why it wasn't spherical like Earth and the other planets. This stumped the team, because from what we know, a celestial body's shape comes from its rotation. The moon's lemon shape suggests that it's rotating quickly, but that isn't the case.
"For the Earth and Mars and other bodies, we know that the dominant shape of the planet is due to its spin," said Garrick-Bethell, the lead researcher of the study. But the moon spins very slowly and is far from the Earth so it is not possible that current tidal pulls could be causing the moon's current shape.
However, when the moon was forming after being flung from Earth after a large impact, it was spinning faster and was closer to Earth. This meant that the Earth's tidal pull on it was stronger than it is now. The moon started out as liquid rock, but after its surface cooled, a hard crust formed on its surface. The liquid, however, remained beneath that. Earth's strong tidal forces tugged at the liquid underneath the surface, creating a bulge. As the moon moved away from Earth and cooled, the bulge froze in place, creating the moon's existing shape.
"If you take a water balloon and start spinning it, it will bulge out at the equator, and on the Earth, we have something very similar to that," said Garrick-Bethell, the lead researcher of the study.
Recently, scientists have been unearthing quite a few discoveries concerning the moon. Not only do we now understand its shape, but we also know what created its dark side, a process involving how one side of the moon cooled faster than the other. It seems we still have much to learn about our moon.
