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Scientists discover the moon is shaped like a lemon

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Our closest neighbor has an "equatorial bulge"

NASA / JPL

Although our visit to its rocky surface confirmed that it's not covered in vast seas, it's not home to strange moon-men, and it's not made of cheese, the moon can still surprise us. It's only this week that scientists have revealed that, 45 years after Neil Armstrong set foot on the planetoid, our closest celestial neighbor is not actually round.

Craters have made working out the moon's shape tricky

It's more of a squashed sphere, with a distinct lump. Ian Garrick-Bethell, who authored the study published in Nature, describes it as "like a lemon with an equatorial bulge," or like a water balloon that flattens out as it's spun. But why, given that it spins much slower on its axis than the Earth and has none of our planet's plate tectonics, is the moon not a perfect sphere? Garrick-Bethell and his team instead ascribed the shape to a process known as tidal heating, in which early orbital forces between the Earth and the moon caused friction in the latter's interior, causing its crust to expand outward in certain places. As the planetoid moved further away from our planet and slowed down its rotation, one such tidal surge was frozen in place, explaining the modern moon's strange bulge.

Garrick-Bethell, a planetary scientist at the University of California, Santa Cruz, used a laser altimeter to create super-accurate maps of the moon's surface, before calculating its topography. The method meant the team behind the study were the first to get a clear picture of the moon's real shape — other scientists who have attempted the same in the past have been foiled by the sheer number of craters pockmarking the planetoid's exterior and concealing its topographical lumps and bumps.