The prospect that life did once exist, still exists and could be sustained in the future on Mars has taken a huge step forward with the confirmation that water ice has been found on the planet.

Water is an essential ingredient for life to survive - without it most of the biological processes needed for life to exist cannot take place.

With the discovery that water is locked in the Martian soil as ice, it makes theories the planet was a much wetter place with liquid water its surface in the past far more likely.

Under these conditions, primitive life could have evolved and - more excitingly - it could still be hanging on in tiny pockets beneath the surface.

For scientists who have spent their careers studying Mars, there could not be a more exciting time to be carrying out their work.

The idea that the planet could have in its past have harboured life, or might still do so, would have been dismissed as a crank in the years that followed the Viking missions to the planet in the 1970s.

Those missions found Mars to be a harsh, dry and sterile place, but more recent and contrasting evidence has enabled the prospect of life on Mars to grow into a mainstream theory among planetary scientists.

Actually obtaining direct samples of life on Mars, however, will be a difficult process.

The traditional tests used to find colonies of bacteria here on Earth involve growing the organism in a laboratory and then identifying it.

Doing such experiments with a robotic lander will be much harder and will instead rely upon searching for key chemicals and gases produced by living organisms.

There is, of course, also the difficulty in finding the right places to take samples from in the first place.

With the water on Mars locked up as ice under the soil, life could be sparse indeed if it is still there, and scientists say it will be like looking for a needle in a planet-sized haystack.

For future missions, the confirmation of water ice on the planet is incredibly important.

Water is heavy and difficult to transport, but for astronauts to set foot on Mars and to establish a base there, as Nasa hopes they will, will require water for them to survive.

Instead of carrying water to the planet in their spacecraft, astronauts may be able to purify water from the ice beneath the soil and use that.

It could provide significant benefits and free up vital space on the first human missions for other equipment and supplies.

So even if the ice on Mars has not supported life on the planet in the past, it certainly could in the future.