I'm sure you know that Earth isn't the only planet in our Solar System; there are actually eight in total. The most Earth-like planet in many ways is Mars, nicknamed the 'Red Planet' because of its red-coloured surface. But it's becoming clear that Mars was actually a blue planet for a long time, covered in lakes, rivers and seas of flowing water, just like Earth!
These amazing pictures were taken by the Mars Express spacecraft, which is orbiting around Mars. They show a riverbed winding across the surface of the planet. This is believed to have been carved by deep, flowing water in the distant Martian past, billions of years before humans even existed!
There is still water on Mars today, although it is frozen under the surface and at the planet’s North and South Poles (like Earth's ice caps). So, this new riverbed might not seem like such an astonishing find, but it's massive!
At 1,500 km long it stretches further than the River Rhine, which runs right across Europe, all the way from Switzerland to the Netherlands! Plus, it's 300 metres deep. That's deeper than any river on Earth!
These new images from the Mars Express give us an exciting glimpse into the past of the red planet, and it doesn't look much different from our own world today!
Scientists believe that billions of years ago Mars suffered the greatest flood in the entire history of the Solar System! It's hard to imagine now, as these days Mars is much too cold, and its atmosphere too thin, for liquid water to survive on its surface.