Researchers from UC Santa Cruz have finally solved the mystery behind the moon's changing shapes. Findings of the study provided significant insight into the moon's early history and orbital evolution.
Study leader Ian Garrick-Bethell, assistant professor of Earth and planetary sciences at UC Santa Cruz, worked with colleagues to revisit the theory of "fossil bulge" and integrated tidal effects to see how the combination would affect the moon's overall shape. The team also factored in their analysis large impact basins known to alter the moon's topography.
"If you imagine spinning a water balloon, it will start to flatten at the poles and bulge at the equator," Garrick-Bethell explained. "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."
Scientists have struggled to study the moon's overall shape due to various impact basins on the moon. These craters have deformed the lunar crust and ejected large amounts of material resulting in variant pieces of research data.
After careful analysis, researchers concluded that the changes in the moon's shape are caused by tidal heating on its poles and frozen tidal-rotational bulges on the remainder of the surface. Due to tidal heating, the poles of the moon become thinner, while the regions facing the Earth have become thicker.
In addition, the researchers observed a misalignment in the moon's overall gravity field and topography by 34 degrees.
"The moon that faced us a long time ago has shifted, so we're no longer looking at the primordial face of the moon," Garrick-Bethell said. "Changes in the mass distribution shifted the orientation of the moon. The craters removed some mass, and there were also internal changes, probably related to when the moon became volcanically active."
Authors of the study admitted that further research is needed to outline the moon's early history and explain the topographical differences between the near and far sides of the moon.
Further details of the study were published in the July 30 issue of Nature.
