The walls on the sides of Zumba Crater on Mars are so steep, it looks like an eyeball staring back at you from the digital terrain model. The ejecta forms a hill of red and brown around the perfectly circular blue crater floor.
Image credit: NASA/JPL/University of Arizona/USGS
This digital terrain model (DTM) is constructed from a stereo-pair of photographs captured by HiRISE on the Mars Reconnaissance Orbiter. The young impact crater burrowed into a hill of its own ejecta on the Martian surface. The crater is quite small, only 3.3 kilometers in diameter, which also means it's very simple with a relatively smooth floor lacking complex structure. The crater floor isn't perfectly smooth: it is carpeted with a deposit type unique to Martian craters. The pitted floor deposit is a mix of shattered rock fragments and glassy impact melts, leftovers from the high-energy, high-temperature impact. We only see it in the youngest, freshest Martian deposits, and haven't found it in any terrestrial or lunar craters (yet!). We think it might have something to do with the interaction of hot melt and ice, so maybe one day we'll see something like it in a fresh Antarctic deposit.
The model is rainbow-coloured by elevation, with a high crater rim peaking in brown and fading down to red, while the deep crater moves through blue into purple on the crater floor. The walls of the crater are so steep that not even a hint of intermediary yellows and greens are visible. The walls rise about 200 meters above the surrounding plane, while the crater floor dives over 600 meters down.
That the crater floor is relatively smooth compared to the surrounding plains marks this as a young, fresh crater. It is also deeper than the average Martian crater by about 25%, again marking itself as very young and not yet infilled with sediments. The steep walls indicate the impact was straight-on, not oblique, as does the relatively symmetrical spray of ejected material.
Using the any-planet impact calculator, a 3-kilometer wide, 0.6 kilometer deep simple impact crater like this on Mars can be formed by a rocky meteorite of about 200 meter diameter travelling at 20 kilometers a second. It could have also been formed by a larger or higher-density impactor moving at a slower speed, or a smaller or lower-density impactor moving at a higher speed. An asteroid travelling at Martian escape velocity, 5 kilometers per second, would need to be just over twice as large, 525 meters diameter, to produce a crater of exactly Zumba's dimensions. A collision of that magnitude occurs approximately every 42,000 years, producing a moderately large shaking (magnitude 7.4) on impact.