University of Arizona | 2019 Jun 12
The moon’s consistent appearance in the sky each night may lull earthlings into a sense of familiarity, but the moon is actually a puzzling place. It lacks an atmosphere and is bone-dry; it can hardly claim a central iron core; and it has a lightweight crust that is chemically similar to Earth.
The best explanation, so far, for the existence of such a world was proposed by two University of Arizona alumni, William Hartmann and Donald Davis, 45 years ago. The idea was inspired by Hartmann’s work as a graduate student under Gerard Kuiper ...
In 1974, Hartmann and Davis proposed what became known as the Giant Impact Theory. They theorized that the moon formed when a Mars-sized planet dubbed Theia – the moon’s Titan mother in Greek mythology – struck Gaia, the early Earth, more than 4.5 billion years ago. The collision, they proposed, flung the top layer of the Earth into space, where the debris recombined to form the moon. ...
The Giant Impact Theory seems to account for the most obvious characteristics of the moon today: No atmosphere, little water and no iron core. Additionally, returned Apollo samples have shown that lunar rocks are chemically indistinguishable from Earth rocks.
On the surface, pun intended, this confirms the 1974 theory. However, computer simulations show that the standard giant impact would create a moon made of the impacting planet Theia, not the Earth, said lunar expert Erik Asphaug ...
