Way back in the Dark Ages, before I got out of graduate school, I took a planetary science course or two at the university. Our field trips were great! We went to places on Earth that had similar characteristics to Mars. That would be deserts, volcanoes, and meteor craters. The West has these in various places, and so over the course of several trips we went to Arizona Meteor Crater, Sunset Crater (a volcano in northern Arizona), the Great Sand Dunes in southern Colorado, and the Big Island of Hawaii, where we studied volcanoes and sapping valleys.

On one of the trips to Meteor Crater we actually had permission to go into the crater to study the layered rocks and the ejecta hurled out when the incoming space asteroid chunk impacted the desert some 50,000 years ago. We were led down by the world’s foremost authority on the crater, the late Dr. Gene Shoemaker. Descending to the bottom of the crater we examined each layer of rock and gleaned its depositional story. Fascinating stuff and a once-in-a-lifetime experience for most of us.

When I saw the latest “rim country” image from the Mars Exploration Rover Opportunity (currently finishing up its exploration of Endurance Crater) I felt transported back more than a dozen years to that hot, dusty day when we explored the layers of Earth’s history in the Arizona desert. The scene here is so familiar that I had a strong memory of Gene’s voice calling out to us across the rock faces and crumbling layers to “come see this!”

This is Mars exploration today, limited by the speed of a couple of slow-moving rovers serving as our eyes and geological tools on the Red Planet. It’s providing tantalizing glimpses of an alien planet that looks so familiar, yet lies so far away. In a funny way, however, looking at pictures like this make me homesick for the wide open spaces we once explored as we readied ourselves to study Mars. I think Gene would say the same thing, but like me, he’d be champing at the bit to go there and see it for himself.

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!