HOW EARTH GOT ITS WATER
A lot of our water likely came from space, which could be shown by a NASA spacecraft that just returned from a nearby asteroid
WORDS ANDREW MAY
DID YOU KNOW? Queen guitarist and astronomer Brian May helped NASA identify a suitable landing spot for OSIRIS-REx
It’s easy to take water for granted on Earth. It surrounds us all the
time – in the sea, in rivers and streams, in rain, in clouds even when it’s not raining and in frozen form as snow and ice in winter. But where did all this water come from? In its earliest days, Earth was extremely hot – maybe as high as 2,000 degrees Celsius – so there couldn’t have been any liquid water on the surface at that time. In fact, there are several scientific theories as to how our planet got its water.
Earth is often described as a ‘water planet’, which is a good description of the way it appears from space, with water, in liquid or frozen form, covering three-quarters of its surface. But if you delve a little deeper, it turns out this is only a superficial impression. Most of our planet is solid rock, with water making up just 0.05 per cent of its mass. Ironically, although Earth is the only place in the Solar System where water is easy to see on the surface, it’s a long way from being the most water-rich body orbiting the Sun.
In fact, water becomes increasingly prevalent the farther out you look in the Solar System, though due to the cold temperatures, much of it exists frozen as ice. But even liquid water may exist in copious quantities deep in the interior of some bodies,
such as Jupiter’s moon Ganymede, where liquid water may make up as much as 46 per cent of its volume. By the time you get to the outermost parts of the Solar System, such as the Kuiper Belt and Oort Cloud, the majority of the material there is in the form of frozen water.