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A research team on board Australia’s Marine National Facility research vessel, Southern Surveyor, have made an unusual discovery: an island that isn’t there.

We rely on maps all the time. Street directories and websites such as Google Maps help us to find our way around unfamiliar places, and help prevent us getting lost. In some situations, accurate maps are more than just a convenience – they are a necessity.

For example, nautical maps used by ships show many hazards such as shallow water, sand bars and coral reefs. Knowing where these are allows a ship’s crew to navigate a safe path to their destination. In case of an emergency, using a map to locate the nearest dry land may be of crucial importance.

‘Sandy Island’ appeared on many maps, including Google Maps and some meteorological maps. It seemed to be a rather large island (28 kilometres long) located in French territorial waters between Queensland and the island of New Caledonia – two places we’re sure are real!

The group of scientists from the University of Sydney, who were leading a research team on board Southern Surveyor, noticed the island wasn’t on the ship’s nautical charts, or on French government maps. The scientists were taking seafloor samples to try to work out the age and history of the seafloor across the Coral Sea.

It was late at night, around 10.30 pm when they arrived where Sandy Island was supposed to be. The captain went slowly for fear of running aground, but lo and behold there was 1300 metres of water below them, and no island!

How this phantom island found its way onto so many maps is not yet clear. What is clear is that a few places are going to have to update their maps, especially as accurate maps are important for nautical safety.

The mystery of Sandy Island shows how important it is to check sources of information. It is also a reminder that direct observation is a good way to confirm what we know. We know so little about our oceans; only 12 per cent of Australia’s territorial waters have been mapped.