There are five oceans on the surface of planet Earth, the largest being named the Pacific Ocean, and between them they contain 97 per cent of the world's water. An ocean is a body of saline (salty) water, and although they cover 72 per cent of the planet's surface, we still know very little about what lies at the bottom of the deep blue sea - in fact we know of only around 230,000 living species of an estimated two million! Oceans aren't just the preserve of Earth though, other exoplanets and moons, such as Enceladus, are thought to have huge bodies of salty water.

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How do corals eat?

Coral reefs house at least 25 per cent of species on Earth despite covering only 0.2 per cent of the ocean floor.

Do fish drink?

Next time you take a dip in the ocean, consider what the fish are drinking and whether you are swimming in urine.