Every planet has its own moons except Mercury and Venus. In our Solar system we got 8 planets (Not including Pluto considered as a dwarf planet) Earth has only 1 moon and some planets have 2-3 or even 67 moons as of Jupiter. Space has a lot of terrestrial bodies revolving around. Earth is not the only planet and our solar system is not the only one, there are billions of Solar Systems like ours and Billions of Stars like Sun (Sun is a star if you know) and also lot bigger than it too. Also many Galaxies Milky way is not the only Galaxy. Space is very big, its doesn't have an end and its known its around 13.8 Billion years old