<Li> 10 Pa (1 femtobar) (night) </Li> <Tr> <Th> Composition by volume </Th> <Td> <Ul> <Li> He </Li> <Li> Ar </Li> <Li> Ne </Li> <Li> Na </Li> <Li> </Li> <Li> </Li> <Li> Rn </Li> </Ul> </Td> </Tr> <Ul> <Li> He </Li> <Li> Ar </Li> <Li> Ne </Li> <Li> Na </Li> <Li> </Li> <Li> </Li> <Li> Rn </Li> </Ul> <P> The Moon is an astronomical body that orbits planet Earth and is Earth's only permanent natural satellite . It is the fifth - largest natural satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits (its primary). The Moon is after Jupiter's satellite Io the second - densest satellite in the Solar System among those whose densities are known . </P>

When was the moon discovered and by whom