If you think you know everything about your neighbor Moon, this is impossible. According to a new research that was published in the journal Nature, Earth's powerful gravity tugged the moon into its oddball shape long ago. The study also reveals that the tidal forces exerted during the initial days of the solar system can speak about the formation of the moon's large-scale topography, including its slight lemon shape.
Researchers believe that the moon formed from debris blasted into space when a mysterious planet-size body rammed into the young Earth. According the scientists, this happened nearly 4.5 billion years ago. The moon was born hot, and it came into existence quite close to our home planet. (The moon has been slowly spiraling away ever since.) The researchers are confident that the newborn moon was thus primed to be sculpted by Earth's gravity.
Lead author of this study Ian Garrick-Bethell and his team carefully studied topographic data gathered by NASA's Lunar Reconnaissance Orbiter and information about the moon's gravity field collected by the agency's twin GRAIL (Gravity Recovery and Interior Laboratory) spacecraft.
The data implicate that tidal effects acted as a key shaper of the moon, said the research team. For instance, tidal forces pulled on the lunar crust, stretching it out and heating it up in places. This process thinned out the crust at the lunar poles and thickened it in the regions that lined up with Earth, helping sculpt the moon into a lemon with two small bulges. One appears on the side facing our planet, the other on the side directly opposite.
Garrick-Bethell said this shape-shifting occurred when the moon's crust was floating on a sea of molten rock. "This happened a long time ago, when the moon was not completely solid," he said. The researcher also concluded that this took place in the first 100 to 200 million years of lunar thermal evolution.