Aluminum and calcium would have more easily condensed in the atmosphere on the colder far side of the moon. Eventually, these elements combined with silicates in the mantle of the moon to form minerals known as plagioclase feldspars, making the crust of the far side about twice as thick as that of the near side.
"Earthshine, the heat of Earth soon after the giant impact, was a really important factor shaping the moon," Roy said.
NEWS: Violent Moon Formation Happened Later Than Thought
When collisions from asteroids or comets blasted the moon's surface, they could punch through the near side's crust to generate maria. In contrast, impacts on the far side's thicker crust failed to penetrate deeply enough to cause lava to well up, instead leaving the far side of the moon with a surface of valleys, craters and highlands, but almost no maria.
"It's really cool that our understanding of exoplanets is affecting our understanding of the solar system," Roy said.
Future research could generate detailed 3D models testing this idea, Roy suggested. The authors detailed their findings June 9 in the Astrophysical Journal Letters.