1The planet Mars has fascinated scientists and writers for more than a century.
2Today, robotic rovers drive very slowly across its cold and dusty surface.
3These robots drill into ancient rocks and study the red soil very carefully.
4Above all, they are searching for signs that liquid water once flowed there.
5Where there was once water, there might also have been simple forms of life.
6Ancient river valleys and empty lake beds can still be seen from orbit.
7The rovers send their photographs and their measurements back to Earth every single day.
8Each picture takes many minutes to travel all the way through space to Earth.
9So far, no clear evidence of past or present life has been found.
10However, the soil does contain useful chemicals that simple living things could use.
11Future missions will bring precious rock samples all the way back to our planet.