With so much knowledge about the Earth's closest companion already in store, scientists have finally unturned a stone on a long-held moon mystery.

According to the New York Times, a new study, published in the journal Nature, suggests the moon is lemon-shaped. Such measurements have been made difficult by the moon's craters, but a team of researchers believes they have finally cracked the code.

"Like a lemon with an equatorial bulge," study lead author Ian Garrick-Bethell, a planetary scientist at University of California - Santa Cruz, told the Times. "If you can imagine a water balloon flattening out as you spin it."

The researchers first obtained topography maps of the moon as accurate as possible with a laser altimeter. They used those maps to create a model of what the moon must have looked like before the craters ever existed.

"When we try to analyze the global shape of the moon using spherical harmonics, the craters are like gaps in the data," Garrick-Bethell said in a press release. "We did a lot of work to estimate the uncertainties in the analysis that result from those gaps."

Garrick-Bethell and his team determined tidal heating, or acceleration, caused part of the moon to appear flattened on one side and enlarged on another.

"There's no plate tectonics like on the Earth," Garrick-Bethell told the Times. "Why is it so deformed?"

Though the moon is not known to spin and should be a round ball of cooled liquid, gravitational forces likely caused the moon's crust to shift as it still spinned.

"The moon that faced us a long time ago has shifted, so we're no longer looking at the primordial face of the moon," Garrick-Bethell said in the release. "Changes in the mass distribution shifted the orientation of the moon. The craters removed some mass, and there were also internal changes, probably related to when the moon became volcanically active."