<P> The origin of the Moon is usually thought to be that a Mars - sized body struck the Earth, making a debris ring that eventually collected into a single natural satellite, the Moon, but there are a number of variations on this giant - impact hypothesis, as well as alternate explanations, and research into how the Moon came to be continues . Other proposed scenarios include captured body, fission, formed together (condensation theory), planetesimal collisions (formed from asteroid - like bodies), and collision theories . </P> <P> The standard giant - impact hypothesis suggests the Mars - sized body, called Theia, impacted Earth, creating a large debris ring around Earth, which then accreted to form the Moon . This collision also resulted in the 23.5 ° tilted axis of the earth, thus causing the seasons . The Moon's oxygen isotopic ratios seem to be essentially identical to Earth's . Oxygen isotopic ratios, which may be measured very precisely, yield a unique and distinct signature for each solar system body . If Theia had been a separate protoplanet, it probably would have had a different oxygen isotopic signature from Earth, as would the ejected mixed material . Also, the Moon's titanium isotope ratio (Ti / Ti) appears so close to the Earth's (within 4 ppm) that little if any of the colliding body's mass could likely have been part of the Moon . </P> <P> Some theories have been stated that presume the Earth had no large moons early in the formation of the Solar System, 4.6 billion years ago, Earth being basically rock and lava . Theia, an early protoplanet the size of Mars, hit Earth in such a way that it ejected a considerable amount of material away from Earth . Some proportion of this ejecta escaped into space, but the rest consolidated into a single body in orbit about Earth, creating the Moon . </P>

Who was the scientist who discovered moon phases