Mars is one of our closest neighbours in space, and people often call it "the red planet." Its surface looks red because the soil contains a lot of iron, which behaves a little like rust. Today Mars is a harsh place: it is extremely cold and dry, with no rivers or oceans on the surface.
However, Mars was not always like this. When scientists look at the planet, they see long valleys and channels that look very much like the ones water creates on Earth. This suggests that billions of years ago, rivers and even lakes may have covered parts of Mars.
This idea matters because, on our own planet, life depends on liquid water. If Mars once had water, it might also have had the right conditions for simple life. To investigate, space agencies send robotic explorers called rovers. These machines move slowly across the surface, drilling into rocks and studying the chemicals inside them. Every sample brings scientists closer to answering one of the biggest questions in science: was there ever life beyond Earth?
