Scientists solve mystery of dark 'streaks' on Mars

Did water once flow on Mars?

That's a question that has puzzled scientists for a long time.

For years, researchers have pictured strange dark streaks running across the dusty Martian surface, with some thinking that could be a sign of liquid.

However, a new study by experts suggests they could be because of something completely different.

Experts at Brown University in the US and the University of Bern in Switzerland decided to take a closer look at the mystery of the dark markings.

These lengthy streaks can form suddenly and fade over a period of years.

On average they are around 600-775 metres long, sometimes branching out and even going around obstacles.

First spotted in the 1970s by Nasa's Viking mission, some scientists have suggested there could be up to two million of these streaks on the planet and that it could be possible evidence of flows of liquid water.

Water is considered an essential ingredient for life, and if true, it could then suggest that the Red Planet could host environments suitable for living organisms.

The team examined about 500,000 slope streaks across Mars for their study which had been spotted in satellite images over time.

Their findings point to the fact that they were likely to have made by fine-grain dust that had been knocked down slopes by wind, meteor impacts or marsquakes - rather than being a sign of water.

Adomas Valantinas from Brown University and co-leader of the study, explained: "The tiny dust particles can create flow-like patterns without liquid.

"This phenomenon occurs because extremely fine dust can behave similarly to a liquid when disturbed - flowing, branching and creating finger-like patterns as it moves downslope."

However, the team did not rule out that liquid might have once existed on Mars.

Valentin Bickel from the University of Bern, who was also involved with the study, added: "Generally, it is very difficult for liquid water to exist on the Martian surface, due to the low temperature and the low atmospheric pressure.

"But brines - very salty water - might potentially be able to exist for short periods of time."