New study explains the Moon's 'lemon shape'

Rather than being a perfect sphere, the Moon is slightly flattened with a bulge at one side, like a lemon. The processes that created our lemon-shaped satellite are uncovered in British scientific journal Nature this week.

Learning how the Moon gained these features could help us to understand other events in lunar evolution. However, attempts to interpret the basic shape of the Moon are hampered by the presence of large basins on its surface that formed after the crust solidified.

To circumvent this issue, American scientists from University of California analysed the topography and gravity outside these basins, and explain the shape of the Moon as the consequence of a combination of two early tidal processes.

The scientists proposed that, the main cause of the squashed shape is a crust-building process controlled by early tidal heating throughout the Moon, while its outer shell was weak enough to be affected by the Earth's tidal forces.

They also suggested that the bulge formed later via tidal forces as the Moon drifted away from the Earth. In addition, an uneven distribution of density in the Moon's interior eventually reoriented its polar axis by about 36 degrees to the configuration we observe today.

The researchers claimed that, their results are the best explanation yet of the Moon's lemon shape.