Curiosity finds disc-shaped features in Mars rocks and prepares to investigate

NASA’s Curiosity rover has found small disc-shaped features in bedrock on Mars, the mission team reported on September 30. The change in rock texture on Mount Sharp has prompted plans for more imaging, composition measurements and a possible drill. The team has not identified the discs or established how they formed.

Planetary scientist Lucy Lim wrote that Curiosity had moved from the finely layered bedrock seen in recent sulfate-unit workspaces to blocks covered, and perhaps filled, with a jumble of the features. The account describes rover work during sols 5016–5021; its Earth planning date of September 18 is distinct from the September 30 publication date.

What Curiosity photographed in the Martian bedrock

A close-up of a brushed patch of bedrock, informally named Salar de Vacas, shows features about 3–4 millimetres across and roughly 1 millimetre thick. Curiosity made the image with its Mars Hand Lens Imager on September 16, sol 5016. The picture combines views taken at different focus positions, bringing more of the uneven surface into focus. A mark in the image came from the rover’s Dust Removal Tool.

Lim said the mission had seen somewhat similar features much earlier near Pahrump Hills, in rocks known as the Murray mudstones. She also noted that comparable shapes occur in some rocks on Earth, particularly where minerals have precipitated from evaporating fluid. Those comparisons provide possibilities to examine; they do not establish that evaporation made the newly photographed discs.

How the rover will test the competing explanations

The mission team planned further Mastcam and Mars Hand Lens Imager pictures to examine the features’ shapes and arrangement. It also planned ChemCam laser-induced breakdown spectroscopy and measurements with the Alpha Particle X-ray Spectrometer to investigate composition. Those observations can add detail about the rocks, but the update says identifying their minerals requires data from Curiosity’s Chemistry and Mineralogy instrument, CheMin.

CheMin examines finely powdered rock or soil using X-ray diffraction, according to NASA’s instrument description. X-rays passing through a sample produce a pattern related to the spacing of atoms in its minerals. Scientists use that pattern to identify the minerals present. This is why the team is considering a drill campaign: imaging and elemental measurements can guide the investigation, while a powdered sample could provide the mineral identification the update says it needs.

NASA says Curiosity’s arm delivers powdered rock or scooped soil to CheMin. The instrument handles up to 85 milligrams in a sample, and an analysis takes 10–30 hours spread over multiple nights. Those figures describe the instrument’s operation; they are not a timetable or a result for this proposed drill site.

Why mineral identity matters at Mount Sharp

Minerals can preserve information about the conditions in which a rock formed or later changed. NASA’s CheMin account explains that temperature, pressure, chemical ingredients and water affect which minerals form. It gives gypsum, which contains water, and anhydrite, which does not, as an example of a distinction the instrument can make. Finding a mineral in the new rocks would therefore give scientists a firmer basis for interpreting them than their disc-like appearance alone.

The broader setting also matters. In a 2022 account of Curiosity’s sulfate-bearing Mount Sharp region, NASA’s Jet Propulsion Laboratory reported diverse rocks and signs of past water. It said scientists hypothesized that some salty minerals were left as ancient streams and ponds dried. That earlier interpretation provides context for examining the new features, but it does not show that these particular discs formed through evaporation.

What happens before Curiosity can drill

The rover had travelled more than a kilometre since its previous drill site at Campo Marte, Lim wrote. The planned campaign would be its first drill above what the team calls the erosional supersurface. The team selected a target and planned a short drive to bring it within reach of Curiosity’s arm, followed by contact measurements. A preload test and drilling would follow only if the earlier steps went well.

Lim said she was due to return to planning for the first drill sol, described as triage contact science. Her update does not confirm that Curiosity drilled, delivered a sample or obtained a CheMin result. Until those steps are reported, the origin and mineral identity of the disc-shaped features remain open questions.