WE NEVER see the farside of the moon. What we see from earth on any day of the month is always the same hemisphere, as it is tidally locked to us, which means it takes the exact same time to revolve around the earth as it does to rotate on its own axis.
Pictures snapped on our many missions around the moon show a striking asymmetry between the two hemispheres. The surface of the hemisphere that faces the earth permanently or the nearside is much more levelled than the farside. The mountainous highlands of the farside have punctured through many theories about the moon’s origin.
According to new research published in Nature, this thick-crusted hemisphere might be the remains of a second moon that coated itself on larger moon in proximity.
This new theory builds on the verified “giant-impact” model that suggests the moon and other smaller satellites formed out of the debris of a collision between the early Earth and a mars sized body.
“Our model works well with models of the moon-forming giant impact, which predict there should be massive debris left in orbit about the earth, besides the moon itself. It agrees with what is known about the dynamical stability of such a system, the timing of the cooling of the Moon, and the ages of lunar rocks,” said Erik Asphaug, one of the authors from University of California, Santa Cruz.
The researchers used precise computer simulation models to back-track the reasons behind the thicker crust of the other half of the moon.
They hypothesised a second impact between the moon and a destabilised companion moon, only this time the process was very slow.
“In such a low-velocity collision most of the colliding material is piled onto the impacted hemisphere as a thick new layer of solid crust, forming a mountainous region comparable in extent to the lunar farside highlands, ” the authors explain.
Curiously such a dynamics do not fit into the general bounds of space collisions, as “it does not form a crater, but splats material onto one side.”