Mars looms large in the scientific imagination, as well as in fiction. Of all the worlds of the solar system, it’s the only one Earth-like enough for exploration with Earth-like tools: Its atmosphere is thin and transparent, its surface is dry and cold, and it’s close enough for regular study. From telescope eyepieces, we’ve probed the Red Planet for centuries. And over the past 50 years, we’ve even sent instruments for a closer look.
However, in geological terms, that’s just a sliver of time. Mars’s deep history remains a mystery.
Read more: Five Martian Mysteries That Have Scientists Scratching Their Heads by Matthew R. Francis