More than four decades after Neil Armstrong made his first steps on the moon, man continues to unravel more mysteries surrounding the Earth's natural satellite. Just this month, a group of researchers led by Ian Garrick-Bethell, from the University of California, Santa Cruz, published a study that revealed the true shape of the moon.

For their study "The tidal-rotational shape of the Moon and evidence for polar wander" which was published in the journal Nature on July 30, Garrick-Bethell and colleagues used highly precise topographic maps of the moon that were made by laser altimeter and made mathematical calculations to determine how the moon's surface looked like before its craters were formed.

The large craters on the moon's surface used to hamper efforts to determine its true shape. The researchers, however, said that they finally know the true shape of the moon, which has been described to be slightly flat with a bulge on one end and which has been likened to the shape of a lemon.

"If you imagine spinning a water balloon, it will start to flatten at the poles and bulge at the equator," Garrick-Bethell said. "On top of that you have tides due to the gravitational pull of the Earth, and that creates sort of a lemon shape with the long axis of the lemon pointing at the Earth."

The researchers also provided an explanation on how the moon's shape was formed. Garrick-Bethell said that changes in the shape of the moon occurred when it was still made up mostly of liquid below a tiny crust of rock. The moon's shape is possibly caused by the gravitational pull of the Earth which raised the tides on the moon and stretched its thin crust during its formation.

"The Moon was [also] spinning much faster," Garrick-Bethell said. "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."

The equatorial bulge, on the other hand, was likely formed at a later time when the moon was still spinning albeit slowing down and moving away from the Earth freezing the rising liquid in place.

"The remainder of the degree-2 topography is consistent with a frozen tidal-rotational bulge that formed later, at a semi-major axis of about 32 Earth radii," Garrick-Bethell and colleagues wrote.

The findings of the study could pave way to knowing when and how the moon was exactly formed.