Final answer:
The Moon did not differentiate to the same degree as Earth due to its lower mass, gravity, lack of internal activity, and inability to retain an atmosphere, leading to a lack of volatiles and distinct geological history.
Step-by-step explanation:
Astronomers believe that the Moon did not differentiate to the same degree as Earth because of several factors. First, the Moon's mass is only one-eightieth that of the Earth, resulting in a surface gravity about one-sixth of Earth's. This low gravity makes it too weak to retain an atmosphere, which means that volatiles, or substances that evaporate at low temperatures, are quickly lost into space. Secondly, the Moon's relative lack of internal activity, absence of air and water, and deficiency in volatiles, unlike Earth, have resulted in a geological history that is quite distinct from our planet.
Although Galileo's observations suggested that the Moon might share some similarities with Earth, we now understand that these are superficial. Unlike Earth, the Moon cannot sustain atmospheres for long, as they are lost by freezing onto the surface or escaping into space. Thus, the geological processes that drive differentiation, such as volcanism and plate tectonics, have not operated in the same way on the Moon.
Finally, theories about the Moon's formation, such as the fission theory or the sister hypothesis, suggest that the conditions under which the Moon separated from or formed alongside Earth did not favor the same level of differentiation observed on Earth.