Nasa scientists may still be celebrating their discovery of liquid water on Mars, but they now face some serious questions about how they can investigate further and look for signs of life on the red planet.
The problem is how to find life without contaminating the planet with bugs from Earth.
Researchers at the space agency are keen for the Curiosity rover to take a closer look at the long dark streaks created by liquid water running down craters and canyon walls during the summer months on Mars.
But the rover is not sterile and risks contaminating the wet areas with earthly bugs that will have hitched a ride to the planet and may still be alive.