The planet Mars gives us such a panoply of different terrains to explore with our spacecraft and rovers. The European Space Agency mission Mars Express has been returning a number of fascinating images based on mapping data from the spacecraft’s instruments. Some of these are so detailed you can see features like sand dunes rippling across the floor of the impact crater Hale in the Argyre Basin of the Martian southern hemisphere. In other places we can spot flow features that look for all the world like the aftermath of a flood or a region cut by a fast-moving river of water sometime in Mars’ distant past.

So, why explore Mars? The most common answer is “because it’s there” is a good one, although it’s tough to convince skeptics of the value of serendipitous exploration. In truth there are dozens of answers. We explore so we can learn. What do we learn from Mars? Its dry and dusty surface holds the keys to a fascinating past that included dramatic planetary reversals of fortune from wet to dry. Can we extrapolate anything we learn at Mars to our future on Earth? Possibly, but it’s not clear that what happened to Mars is waiting in store for Earth. We can, however, take what we know at Earth and apply it to Mars. We know how flowing water changes surface characteristics here on the home planet, and when we see it on Mars, we know how it happened. Same with volcanic flows and impact cratering and wind-driven erosion. All those things happen here on Earth, and we know what they look like here. Find the same kinds of structures on Mars and you have a good lead as to what happened ON Mars.

That’s the beauty of exploration—you learn and then you take what you know and apply it elsewhere to understand how things work in the cosmos. Mars is giving us a lot of mysteries, but it’s also allowing us to do some practical planetary science, all for the price of some useful missions!