Curiosity has been rolling through finely layered sulfate bedrock for weeks, so when the rover's cameras returned images of small disc-shaped lumps covering rock blocks instead of the expected laminations, the science team sat up. The features — 3-4 millimeters across, about 1 millimeter thick — aren't entirely unprecedented. Similar morphologies appeared near Pahrump Hills early in the mission, and they show up on Earth in evaporite settings where minerals precipitate as a fluid dries out. Two competing hypotheses are on the table: the discs could reflect the crystal growth habit of a specific mineral, or they could be fragments of a harder layer that broke apart and accumulated. The blog post by planetary scientist Lucy Lim (NASA Goddard) walks through five sols of planning — Sols 5016 through 5021 — with the methodical cadence that defines Curiosity operations. The team hit the new texture with everything available on the arm: MAHLI close-up imaging of targets informally named "Yungay" and "Chiu Chiu," LIBS laser shots on "Puya Raimondii," "Liolaemus Tacnae," and "Pisqu Warkatana," and APXS on "Salar de Vacas" for elemental composition. Each instrument answers a different question, and none alone settles the mineral identity. For that, Curiosity needs CheMin — the X-ray diffraction instrument that can actually identify crystalline minerals. CheMin requires a drilled powder sample, which means a full drill campaign. The rover hasn't drilled since Campo Marte, over a kilometer back, making this the first drill above the erosional supersurface that marks a major geological boundary on Mount Sharp. The team drove to a promising workspace, characterized the site with arm instruments on targets "Alberta Wild Rose" and "Moonraker Mountain," and selected a specific drill target. The long-distance imaging program continued in parallel. ChemCam's Remote Micro-Imager and Mastcam captured mosaics of buttes flanking Valle Grande — essentially cross-section views of the rock layers above the rover's current position. These "cutaway" images will help map sedimentary structures in units Curiosity hasn't reached yet and piece together the erosional history of Valle Grande itself. What makes Curiosity's blog posts quietly remarkable is how they expose the actual logic of planetary field geology in real time. You see the decision tree: unexpected texture triggers compositional investigation, compositional investigation reveals instrument limits, instrument limits necessitate drilling, drilling requires driving and site characterization. The science isn't a revelation announced from on high — it's a sequence of constrained choices made by a team working with a robot 140 million miles away, naming rocks after South American landmarks and Canadian wildflowers. The MAHLI focus-merge image from Sol 5016 — a composite stitched from multiple focal depths — is the visual anchor of the post. It shows the brushed spot on "Salar de Vacas" with the disc-shaped features in sharp relief and a small divot from the Dust Removal Tool. At this resolution, Mars geology looks almost tactile. The discs are tantalizing precisely because their origin isn't settled. Crystal growth? Mechanical accumulation? The answer matters for understanding whether liquid water was present, how it behaved, and how long it lasted.
