SANTA CRUZ, Calif., July 30 (UPI) -- Neither the Earth nor its moon are a perfect sphere. Scientists have know this. But while the Earth's slightly elliptical shape has been explained by its rotation and the gravitational pull of the moon, these factors didn't entirely explain the Moon's lemon-like form. And astronomers remained a bit puzzled -- until now.
Researchers at the University of California, Santa Cruz (UCSC) say that tidal forces early in the moon's formational history account for its odd appearance. Today, the moon rotates too slow and is too far from Earth to explain its flattened shape. But in its earliest days, while still predominantly liquid, the moon was closer and spinning faster. The sculpting effects of these two factors were frozen into place as the moon solidified and matured.