The Earth-Moon system’s history remains mysterious. Scientists believe the two formed when a Mars-sized body collided with the proto-Earth. Earth ended up being the larger daughter of this collision and retained enough heat to become tectonically active. The Moon, being smaller, likely cooled down faster and geologically ‘froze’. The apparent dynamism of the Moon challenges this idea. New data suggest this is because radioactive elements were distributed uniquely after the catastrophic Moon-forming collision.
New data suggest this is because radioactive elements were distributed uniquely after the catastrophic Moon-forming collision. Earth’s Moon, together with the Sun, is a dominant object in our sky and offers many observable features which keep scientists busy trying to explain how our planet and the Solar System formed. Most planets in our solar system have satellites. For example, Mars has two moons, Jupiter has 79 and Neptune has 14. Some moons are icy, some are rocky, some are still geologically active and some relatively inactive. How planets got their satellites and why they have the properties they do are questions which could shed light on many aspects of the evolution of the early Solar System.
The Moon is a relatively cold rocky body, with a limited amount of water and little tectonic processing. Scientists presently believe the Earth-Moon system formed when a Mars-sized body dubbed Theia — who in Greek mythology was the mother of Selene, the goddess of the Moon — catastrophically collided with the proto-Earth, causing the components of both bodies to mix.
The debris of this collision are thought to have fairly rapidly, perhaps over a few million years, separated to form the Earth and Moon. The Earth ended up being larger and evolved in a sweet spot in terms of its size being just right for it to become a dynamic planet with an atmosphere and oceans. Earth’s Moon ended up being smaller and did not have sufficient mass to host these characteristics. Thus retaining volatile substances like water or the gases that form our atmosphere, or retaining sufficient internal heat to maintain long-term planetary volcanism and tectonics, are idiosyncratic to how the Earth-Moon forming collision occurred. Decades of observations have demonstrated that lunar history was much more dynamic than expected with volcanic and magnetic activity occurring as recently as 1 billion years ago, much later than expected.
A clue as to why the near and far side of the Moon are so different comes from strong asymmetry observable in its surface features. On the Moon’s perpetually Earth-facing near side, on any given night, or day, one can observe dark and light patches with the naked eye. Early astronomers named these dark regions ‘maria’, Latin for ‘seas’, thinking they were bodies of water by analogy with the Earth. Using telescopes, scientists were able to figure out over a century ago that these were not in fact seas, but more likely craters or volcanic features.
Back then, most scientists assumed the far side of the Moon, which they would never have been able to see, was more or less like the near side.
Story Source: Materials provided by Tokyo Institute of Technology. Note: Content may be edited for style and length.