Alien hunters claim to have seen running water in these NASA images of Mars.

The US space agency is weighing up how to use the Curiosity Rover, which is exploring the planet, to collect samples of running water on the surface.

But is concerned that Earthly bacteria on the droid will get into the Martian water - potentially starting "alien" life to form on the planet.

A NASA spokesman said: "Ever since it was announced that there may be evidence of liquid water on present-day Mars, NASA scientists have wondered how best to further investigate these long, seasonally changing dark streaks in the hope of finding evidence of life – past or present – on the Red Planet."

Jim Green, NASA’s director of planetary science, said: "It’s not as simple as driving a rover to a potential site and taking a scoop of soil.

“Not only are these on steep slopes, we need to ensure that planetary protection concerns are met. In other words, how can we search for evidence of life without contaminating the sites with bugs from Earth?”