Huge Impact May be Why the Moon's Near and Far Sides Differ So Much
upstart writes:
Huge Impact May Be Why The Moon's Near And Far Sides Differ So Much:
When spacecraft first journeyed around the Moon, something unexpected was revealed: the far side has almost none of the lava flows we call seas or maria, which dominate what we can see from Earth.
For almost 60 years, astronomers have sought to explain the discrepancy with many different theories. A new model proposes the answer lies in the Moon's largest and deepest impact crater.
The lunar seas are the result of immense lava flows that erupted recently enough they have not been completely covered in craters. The puzzle is why there were so many more such eruptions on one hemisphere than the other.
A new study in the journal Science Advances proposes that the formation of the South Pole-Aitken (SPA) basin triggered a heat plume in the lunar interior that produced the imbalance. The SPA is among the Solar System's largest impact basins, with a metal structure beneath that may be the asteroid that formed it. The SPA is not as well known as smaller lunar craters, both because it's on the far side, and its immense age (4.3 billion years) means subsequent impacts have partially obscured it.
[...] For much of the time since the absence of seas on the far side was discovered, attempts to explain the difference centered on the relationship of the two hemispheres to Earth. Examples include efforts to explain how Earth's gravitational field could have produced greater activity on the lunar near side, or the planet's bulk blocked incoming asteroids, reducing cratering.
However, if the study authors are right, it's all a coincidence, a consequence of where the impact that caused the SPA happened to take place.
Journal Reference:
Matt J. Jones, et. al., A South Pole-Aitken impact origin of the lunar compositional asymmetry, (DOI: https://www.science.org/doi/10.1126/sciadv.abm8475)
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