Nasa: Mars has flowing water

Scientists at Nasa say they think they've identified new evidence of flowing water on Mars, the crucial component for sustainable life - and potential human colonisation one day.

Their excitement comes after analysis of satellite images that show small trails of salty liquid water running down slopes on the Red Planet. ITV News Science Correspondent Alok Jha reports:

• More: Ten key moments in the effort to understand Mars

Nasa have tweeted a short video outlining the key points of the discovery of liquid, salty, water on the surface of Mars.

"Mars is not the dry, arid planet we thought of in the past," Nasa says.

• Pictures: 'Dark, narrow streaks' show the flow of water on Mars

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Photographs released by Nasa show the dark, narrow streaks that scientists say are formed by the flow of briny, liquid water across the surface of Mars.

The experts are unsure where the water comes from, but think it may rise up from underground ice or salty aquifers, or condense out of the thin Martian atmosphere.

• Seasonal Mars landscape changes shaped by 'water activity'

Nasa has discovered that liquid water "almost certainly" exists on the surface of Mars.

It's not known where the extremely salty water comes from, with theories including the melting of 'near-surface ice', seasonal discharges from layers of water-bearing rock or absorption from the Martian atmosphere.

"It is conceivable that RSL are forming in different parts of Mars through different formation mechanisms," said the scientists.

• More: Ten key moments in the effort to understand Mars

Nasa have announced that liquid water "almost certainly" exists on Mars.

In a press conference, the space exploration agency said it has discovered that seasonal changes to the Martian landscape are caused by flowing water on the surface of the planet.

"Under certain circumstances, liquid water has been found on Mars" - Nasa Planetary Science Director Jim Green, said in the briefing.

Liquid water on the surface of Mars could support life and "may affect future human exploration," according to Nasa.

The live announcement has now ended.

• More: Ten key moments in the effort to understand Mars

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Mysterious features on Mars that change with the seasons are almost certainly created by flowing liquid water, scientists at Nasa believe.

Latest satellite images have identified narrow streaks, typically less than five metres (16.4 ft) wide, that appear on slopes during warm seasons, lengthen, and then fade when conditions become cooler.

Experts have speculated that water might be involved in the formation of the gully-like features, known as recurring slope lineae, but only now has evidence supporting the theory come to light.

Liquid water could suggest that the surface of Mars is able to support life.

Nasa wrote: "Water is essential to life as we know it. The presence of liquid water on Mars today has astrobiological, geologic and hydrologic implications and may affect future human exploration."