The it, in your example, refers to the state of being a creature of pure space.
looked it, in this instance, is used to give emphasis to the the previous observation.
He was completely exhausted from traveling across the desert for eight days, and he looked it.
The emphasis relies on the idea that looks can be deceiving. So someone could be a creature of pure space and yet not look it.
For example, the Emperor of Japan in the mid to late 19th century lived in a great palace and was dressed in the finest silks, waited on hand a foot, etc. He looked like a descendant of the Sun Goddess.
Saigo Takamori, on the other hand, was a politician and military officer of some renown and high standing, but he did not look it. In fact it has been reported on one occasion that when he left the Emperor's palace that he was arrested because he looked of such lowly standing the guard did not believe he could have any business being in the palace.