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perseverancerover·NASA's Perseverance Mars RoverbySpecialSetOfSieves

Is the "purple coating" forming on Percy today? (Update - possible explanation)

Since the earliest weeks of the mission, the science team has been documenting an interesting type of feature found on many of the rocks Perseverance has encountered, dubbed the "purple coating". This has often been found on rocks that have been abraded by the rover (e.g. abrasion patches #2, left, and #18, right)...

... as well as natural, untouched surfaces. Some of these feature truly bizzare patterns:

The terrain being explored by Perseverance in Jezero Crater and Nili Planum is unique to date in our explorations of Mars, in that these coatings seem to be very widespread here. A much smaller number of rock coatings which may or may not be similar were found by Spirit and Opportunity, but Curiosity has notably found none. A 2025 paper by Garczynski et al. offers an explanation for these coatings - "indurated dust".

This "indurated" (solidified) coating forms may form in a series of steps:

  • Windblown dust and very fine soil particles settle onto a rock
  • Electrostatic charges may make the dust "clump" and stabilize on the rock surface
  • Sand buries the stabilized dust
  • Humidity beneath the sand increases under certain scenarios (e.g. frost formation events)
  • The water reacts with iron and sulfur-bearing minerals in the deposited dust and soil, "cementing" it into a thin coating

This recent image captured by MastCam-Z shows a material very reminiscent of the purple coating on the rover's deck, near the base of the mast. If this material is related to the purple coating, it may have formed fairly recently. To my mind, the flat and homogeneous appearance of the material resembles the kind of thin layer you'd expect would form first.

Perseverance was parked for 46 sols (Earth dates 11 December 2025 to 28 January 2026) during solar conjunction, when the Sun prevented communication between Earth and Mars. Crucially, these dates correspond to late summer and early autumn in this region, when humidity is known to be high (as the longer, warmer days evaporate the north polar ice cap). Given the amount of fine regolith and dust that the wind has deposited onto the rover deck, and the relatively gentle slopes of the terrain we've been exploring in the last few months, it is conceivable that the loose material simply hasn't moved much recently, thus "sheltering" the deck, the same way sand can shelter the rocks where the coating has formed.

If correct, this observation of a coating on the body of Perseverance has interesting implications. It would mean that the coating can form quite quickly, and that this process is occurring today, not millions of years ago. Water actively altering the surface of Mars (and our rover) today is something we must observe closely, for many exciting reasons. If this process is active on an exposed and seemingly unsuitable surface like the rover deck, one wonders how widespread it is in the soil...

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perseverancerover·NASA's Perseverance Mars RoverbySpecialSetOfSieves

Drive report (sol 1765) - 2 h, 200 m

::: spoiler Further post-drive info for mission context :::

Updated maps of Percy’s whereabouts as of this sol below. The outer rim of Jezero Crater is to the right.

The sites of the two most recent rock abrasions, #50 and #51, are labelled (red boxes) above.

In the higher-resolution view above, local features are visible, such as the field of mega-ripples to the rover's northeast, two small craters with dark sandy floors to the east, and the "bench" of lighter-toned, flat, fractured bedrock now below the rover's wheels.

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perseverancerover·NASA's Perseverance Mars RoverbySpecialSetOfSieves

Quartz-rich rock? (sol 1764)

For context:

A number of quartz-rich "white rocks" have been found by Percy since late 2024, and this may be the latest example.

Quartz is not uncommon on Mars - it's a component of the volcanic rock you'd expect to find almost anywhere on Mars - but it has been quite rare to find it in isolation on this planet, making up all or most of a rock. Some of the latest published research proposes that these white rocks were left behind after the hot water of a hydrothermal system flowed through this crater rim area, which is definitely plausible, given all the other water-altered minerals we've found in the region.

Of course, you're probably not going to read this preamble anyway, and the unscientific comments will begin to flow shortly. So let me just say here and now that Martian sandworms are disgusting creatures, leaving garbage like this behind. Shoot them on sight, Percy!

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perseverancerover·NASA's Perseverance Mars RoverbySpecialSetOfSieves

Latest drive (sol 1762) - 150 m

::: spoiler Further post-drive info for mission context :::

Updated maps of Percy’s whereabouts as of this sol below. The outer rim of Jezero Crater is to the right. The sites of the two most recent rock abrasions, #50 and #51, are labelled in the first. The rover’s current position is marked with a cross. The second image is a higher-resolution view of the rover's immediate environs.

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