Scientists Explain why Moon is Shaped Like a Lemon

Researchers explain why moon has an odd shape.

The team at the University of California, Santa Cruz, found that early tidal effects shaped the moon. The study could also explain the satellite's origin as well as its orientation in space.

Previous research has shown that a relatively "mild" cosmic collision gave rise to Earth's moon some 4.5 billion years ago. Earth's gravity molded a mass of ejected rock into the moon that we see today. But, the gravitational pull of our planet doesn't fully explain why the lunar surface has an odd shape.

Back in 1898, scientists proposed an idea known as "fossil bulge" hypothesis to explain the bulge on the lunar surface.

"If you imagine spinning a water balloon, it will start to flatten at the poles and bulge at the equator," said Ian Garrick-Bethell, assistant professor of Earth and planetary sciences at UC Santa Cruz, according to a news release. "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 involved in the current study said that the bulge hypothesis doesn't entirely explain the deformed shape moon. The team incorporated tide effects as well as accounted for large impact basins. The team even used data about moon's gravity and topography.

According to the researchers, the moon probably got its squashed appearance due to a gravitational process called tidal heating. The tidal heating stretched the lunar surface; the bulge could have occurred at a later period when the moon was still spinning but had slowed down a bit. As the moon drifted away from earth, a tidal surge got frozen in place, The New York Times reported.

The study is published in the journal Nature.