And how do they form?
I know there have been many missions to the moon and it's incredible to think humans have walked on its surface!...
Normally, when stuff collides, things fly apart from each other. So how did planets form in the first place?
Space is full of stars giving off huge amount of energy. So, why is it so chilly?
Where are we within the universe? Joanna Kerr asks
astrophysicist Dr Sean McGee from the University of