Scientists have discovered 'oceans' of water 12 miles below the surface of Mars which could potentially harbour life.

Seismic data from NASA's Insight lander indicates deep, porous rock filled with liquid water that experts predict would cover the entire red planet to the depth of around a mile.

But the underground reservoir is just too deep to drill into with current technology – dashing hopes it could help sustain any future Martian settlers.

It is understood that oceans disappeared from the surface of Mars more than three billion years ago.

The newly-discovered water is being held in tiny cracks and pores in rock in the middle of Mars' crust, between 7 and 12.5 miles below the surface.

Drilling a hole even a mile deep is a major challenge, even on Earth.

The geophysicists say their findings, published in the journal Proceedings of the National Academy of Sciences, do pinpoint another promising place to look for life on Mars – if it can one day be accessed.

The discovery also helps answer questions about the geological history of the planet.

Dr Vashan Wright, from the University of California San Diego, said: 'Understanding the Martian water cycle is critical for understanding the evolution of the climate, surface and interior.

'A useful starting point is to identify where water is and how much is there.'

Their analysis of seismic data led to the conclusion there is a deep layer of fractured igneous rock – cooled magma – saturated with water.

Co-author Professor Michael Manga said: 'Establishing that there is a big reservoir of liquid water provides some window into what the climate was like or could be like.

'And water is necessary for life as we know it. I don't see why [the underground reservoir] is not a habitable environment.

'It's certainly true on Earth – deep, deep mines host life, the bottom of the ocean hosts life.

'We haven't found any evidence for life on Mars, but at least we have identified a place that should, in principle, be able to sustain life.'

Professor Manga said that lots of evidence - river channels, deltas and lake deposits, as well as water-altered rock - supports the theory that water once flowed on the surface of Mars.

But that wet period ended over three billion years ago, after Mars lost its atmosphere.

Planetary scientists have sent probes and landers to the red planet to find out what happened to that water.

They say that the water frozen in Mars' polar ice caps can't account for it all - nor when it happened, and whether life exists or used to exist on the planet.

The new findings indicate that much of the water didn't escape into space, but instead filtered down into the crust.

The Insight lander was sent by NASA to Mars in 2018 to investigate the crust, mantle, core and atmosphere. The mission ended in 2022.