When lost on another planet, our little green friend reminds us: Remember your training. Save you it can.

I’m not surprised that Mars Guy is going back to the textbook, so to speak, because we just don’t have experience with a geologic setting quite like this - the moderately well-preserved rim of a ~50 km-diameter impact crater - from prior Mars exploration or Apollo (Earth, of course, has done a lousy job of preserving craters of this size). The closest example is Opportunity’s exploration of Endeavour Crater, which is much smaller, with a far smoother, more degraded rim. Apollo 15 landed near the edge of the Apennine Mountains, formed by the immense Imbrium basin impact (~1100 km diameter), but the astronauts didn’t have the chance to ascend the foothills to any great height during their short and very busy stay. Opportunity had access to extensive outcroppings of bedrock at Endeavour, not to mention the kind of smooth, light-toned “paver stones” that Curiosity and Perseverance have been driving over for years. The Apollo astronauts saw nothing of the kind, unsurprisingly - the Moon being completely blanketed by that powdery surface.

Those other landing sites feature nothing quite like the distinct, boulder-studded knolls and ridges that Percy is investigating, which seem related to the original crater formation process itself. These gentle hills roughly follow the regional SW to NE trend of the rim mountain Percy is climbing (zoom in just a bit on the ESA map to see the steep face of the spur north of the rover), and several feature intact, massive blocks of bedrock that I’d love to sample (see Paul Hammond’s Pico Turquino post for the best example yet). Good episode by Mars Guy, and I can’t disagree with him here for the most part, but believe me, he isn’t laying the hardcore stuff on us yet: impact crater geology melts brains, not just rocks!