This area of Mars was once a volcanic plain. The surface here is not dissimilar to volcanic plains on the Earth, where large sheets of lava cover the landscape. Just like on the Earth, you can also see the evidence for individual lava flows and pools of lava, long since cooled into interesting shapes.

Unlike on Earth, there are lots of craters on this lava plain, and you might notice that some of the craters have dark interiors and a spray of darker material around them, but most don't. This difference is telling you something about the difference in age of these craters. These lava flows are composed of dark rock, but lighter-colored dust blows everywhere on Mars (and shows as gray in our black and white images). So old structures and craters have been blanketed in a layer of dust. But when a new crater forms, it punches a hole into the dark lava rock underneath, and so fresh craters on this landscape will have dark interiors showing fresh rock, but over time, the dust will blow around and coat those craters, too.

Some larger craters in this scene have a dark interior, not because they are young or fresh, but because they are big enough to have slightly steeper slopes and so even though dust is blown into the crater, fresh dark lava rock avalanches to the floor or is eroded into dark sand that stays in the crater.

Written by: Ross Beyer  (21 July 2023)