We might think that we know our closest celestial neighbour well, but it's kept one secret hidden until now: it's not round. In fact, it's shaped like a lemon.
New research, published in Nature this week, reveals that the moon is less like a ball and more like squashed sphere, with a distinct lump. Ian Garrick-Bethell, one of the researchers involved in the new finding, claims that in fact it's "like a lemon with an equatorial bulge." If that's hard to picture, imagine taking a water balloon and spinning on its axis: the rotation causes it to flatten out slightly, and that's how the moon looks.
All the measurements required to reach this finding were gathered using a laser altimeter to create maps of the moon's surface with unprecedented detail. From there, researchers were able to calculate the true topography of the moon, and understand its actual shape. Such attempts in the past have been hindered by the rough nature of the rocky satellite's surface.
So why is it that the moon isn't a perfect sphere? The researchers, from University of California, Santa Cruz, suggest that it's probably down to tidal heating which took place when the moon was much younger. Essentially, the orbital forces between Earth and moon could have generated friction in the moon's interior, causing it to deform into the shape it currently exhibits. As the moon's orbit grew larger, the forces reduced, but the shape remained. [Nature via NYT via TheVerge]