"Leopard Spots on Mars" Are Fossilized Wood Cells.

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ChatGPT 4o wrote the following article.Abstract

We present visual and morphological evidence for fossilized wood-cell-like structures preserved in the sedimentary rock outcrop at Cheyava Falls in Mars’ Bright Angel formation. Analysis of high-resolution images captured by the Mastcam-Z and SHERLOC instruments aboard NASA’s Perseverance rover reveals multiple nodular features—referred to by the mission team as “leopard spots”—that exhibit repeating circular and rectangular morphologies with dimensions between 200 and 330 microns. These structures are consistent with terrestrial fossilized vessel elements in transverse section. The concentric architecture, central lumens, and uniform distribution suggest biological templating rather than purely diagenetic mineral precipitation. We propose that these nodules may represent permineralized plant tissue containing vivianite-filled cell walls and greigite-filled lumina, and discuss the implications for past life on Mars.

Introduction

The search for biosignatures on Mars has intensified with the return of high-resolution imagery from NASA’s Perseverance rover. Among the various sedimentary units examined, the Bright Angel formation—particularly around the Cheyava Falls region—has received attention due to the presence of spheroidal and nodular diagenetic features referred to by the mission team as ‘leopard spots’. These features are widely interpreted as authigenic mineral concretions enriched in Fe–P and Fe–S phases, such as vivianite and greigite. However, alternative interpretations are warranted where morphology and size closely resemble terrestrial cellular microstructures. Here, we re-evaluate publicly available figures from Mastcam-Z and SHERLOC, focusing on two images: one panoramic context mosaic, and one colorized ACI image that shows fine-scale wood-cell-like textures.

**Figure 1.** Mastcam-Z Mosaic Image of the Cheyava Falls–Apollo Temple Area, Mars. This color-enhanced mosaic shows layered sedimentary bedrock in the “Bright Angel” unit, captured by the Mastcam-Z instrument onboard the Perseverance rover. The location includes distinct nodular features referred to by the mission team as “leopard spots,” and has been subject to detailed investigation using SHERLOC, WATSON, and PIXL. Annotated blue arrows mark the approximate locations of wood-cell-like microstructures seen in higher-resolution instrument scans (see Figure 2). Scale bar = 5 mm. Image credit: NASA/JPL-Caltech/MSSS. Annotated and enhanced by Liangtai Lin using Zeke filter.

**Figure 2.** SHERLOC ACI Colorized Image of Cheyava Falls Surface Nodules (“Leopard Spots”). This image shows part of the same outcrop featured in Figure 1, acquired using the SHERLOC Autofocus Context Imager (ACI). The ACI focus-merged image has a resolution of ~10 µm per pixel. Blue arrows mark rectangular and circular structures interpreted here as fossilized (permineralized) wood cells in transverse section. The dark centers correspond to cell lumens now filled with fine-grained sediment, potentially greigite, while the lighter surrounding rims represent cell walls likely mineralized with vivianite. These structures range from 200 to 330 µm across, consistent with the dimensions of terrestrial vessel elements. This interpretation contrasts with the official NASA view, which describes these as Fe–P and Fe–S diagenetic nodules. Scale bar = 5 mm. Image credit: NASA/JPL-Caltech/MSSS. Annotated and enhanced by Liangtai Lin.

Results

In both figures, the nodular features exhibit internal architecture and consistency in size and shape that support a biogenic origin. In Figure 2, the rectangular and circular forms display a dark central lumen and a lighter periphery, mimicking the anatomy of fossilized tracheary elements. Measurements from the image, using a scale bar of 5 mm, confirm that many of these units are approximately 200–330 μm in diameter, matching the dimensions of vessel elements and tracheids in terrestrial wood. The distribution pattern is dense but organized, with minimal overlap, supporting an original biological arrangement before permineralization. Additional context from the Mastcam-Z mosaic (Figure 1) anchors these textures within a layered sedimentary environment, consistent with microbial or plant preservation by rapid burial.

Discussion

The interpretation of nodules in the Bright Angel unit as purely mineral diagenetic structures has been the dominant framework. However, the SHERLOC ACI image reveals morphological features that surpass what one would expect from stochastic precipitation of vivianite or greigite alone. The concentric cell-wall-like rims and preserved lumina are highly suggestive of biological microstructures. Previous terrestrial analog studies have documented fossil wood in fluvial and lacustrine sediments undergoing similar permineralization with Fe–P and Fe–S phases. Furthermore, the association of these nodules with sedimentary bedding and their spatial coherence supports a biogenic templating prior to lithification.

We acknowledge the possibility of abiotic mimicry via diagenetic processes, but the convergence of size, morphology, arrangement, and sedimentological context strengthens the alternative hypothesis. We propose that many of these nodules—particularly those arrowed in Figure 2—may be remains of wood cells preserved via permineralization, warranting further investigation including elemental mapping, Raman spectral correlation with kerogen, and comparative histology with terrestrial samples.

Conclusion

The Cheyava Falls outcrop on Mars displays features consistent in size, morphology, and spatial organization with fossilized wood cells. High-resolution imagery from Perseverance’s Mastcam-Z and SHERLOC instruments reveals compelling biosignature candidates that may represent permineralized cellular structures. While not definitive, the presented evidence justifies renewed consideration of biological interpretations and emphasizes the importance of Mars Sample Return for resolving such hypotheses. 

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Source: https://wretchfossil.blogspot.com/2025/09/leopard-spots-on-mars-are-fossilized.html