Moon mystery: Why our Earth's satellite is lemon-shaped
Scientists have worked out the reasons for the distorted shape of our Moon. A US team calculated the effect on the shape of the early Moon of tidal and rotational forces. They say its own spin and the tidal tug of the Earth created a "lemon-shaped" satellite. This shape-shifting occurred when the Moon was mostly liquid beneath a thin outer crust of rock.
"For the Earth and Mars and other bodies, we know that the dominant shape of the planet is due to its spin," he said. "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." This effect, however, does not explain how "surprisingly distorted" our Moon is.
"It's spinning really slowly, and it's really far from the Earth, so it's not like tides today could be causing that." Prof Garrick-Bethell's new explanation is that four billion years ago - when the Moon formed from the debris thrown out by a huge impact between early Earth and a so-called planetoid - was much closer to the Earth. This meant tides were stronger.
"The Moon was also spinning much faster," he told BBC News. "So there's a variety of interesting things that could happen, at that time when the Moon was really hot, that could change its shape."