Evidence of Fossilized Wood-Like Ultrastructure in Asteroid Ryugu Material

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Rebuttal: On the Plausibility of Alternating Saponite and Serpentine Lamellae

A common counterargument proposes that the nanostructures observed in Ryugu particle C0068—specifically the alternating 0.7 nm and 1.1 nm lamellae—may result from linear intergrowths of known phyllosilicate minerals such as serpentine and saponite. However, this interpretation lacks precedent in mineralogy and crystallography. Serpentine and saponite are both phyllosilicates, but they belong to different structural families (1:1 vs. 2:1 layer types, respectively) and form under distinct physicochemical conditions. Their lattice parameters, hydration behavior, and substitution chemistry are incompatible with regularly alternating nanoscale layering. To date, no peer-reviewed geological study or experimental synthesis has reported such periodic intergrowths between these two minerals.

The Britannica AI chatbot itself acknowledges that no evidence was found in the source material for linear or alternating arrangements of saponite and serpentine. The absence of such patterns in nature suggests that the organized lamellar nanostructure in Fig. 1C is not the result of known abiotic crystallization processes. Instead, the periodicity, scale, and alignment of the lamellae are more consistent with biological ultrastructures, such as the S2 layer of lignocellulosic secondary walls in wood. The observed spacing (~0.7–1.1 nm) closely matches the known dimensions of cellulose microfibril separation in terrestrial plant tracheids, as shown in Fig. 2. These findings support the hypothesis that the Ryugu C0068 particle may preserve fossilized remnants of biological cell wall architecture, rather than a purely mineralogical intergrowth.

Evidence of Fossilized Wood-Like Ultrastructure in Asteroid Ryugu Material: A Comparative Analysis with Terrestrial Cell Walls

Introduction

Asteroid Ryugu, a carbonaceous near-Earth object, has yielded intriguing mineralogical and microstructural data through the Hayabusa2 mission. Recent high-resolution analyses have revealed potential biogenic-like features in particles returned from its surface. Among these, one sample—designated C0068—has garnered special attention due to the presence of repeating nanoscale lamellae. These lamellae are comparable to the multilayered ultrastructure of terrestrial wood secondary cell walls.

Figure 1. (A) Combined X-ray map of a dry-polished Ryugu C0068 section showing elemental distribution (Mg = red, Ca = green, Fe = blue). (B) Backscattered electron image of the boxed region in (A) with mineral labels. (C) High-resolution TEM image showing intergrowth of saponite and serpentine with 0.7 nm and 1.1 nm lattice fringes, respectively. These repeating lamellae suggest an organized ultrastructure. Their size, arrangement, and spacing invite comparison with Earth wood cell structures.

Comparative Results

The layered structures observed in the high-resolution TEM image of Ryugu sample C0068 (Fig. 1C) exhibit periodicities of 0.7 nm and 1.1 nm—dimensions consistent with the spacing between cellulose microfibrils and matrix polysaccharides in the S2 layer of terrestrial tracheid cell walls. This resemblance suggests the possibility that the asteroid sample preserves a fossil-like record of organized, potentially organic, lamellar material.

To reinforce this interpretation, we compare the Ryugu ultrastructure to a TEM image of terrestrial Pinus radiata wood (Fig. 2A), as well as a schematic model (Fig. 2B) illustrating the S1, S2, and S3 layers in secondary cell walls. The S2 region, rich in cellulose fibrils, is marked by vertical stripes similar in periodicity to the intergrowths in the Ryugu sample.

Discussion

While abiotic mechanisms such as phyllosilicate intergrowth or clay crystallization can produce nanoscale periodicities, the consistent spacing, linear alignment, and contextual mineralogy in Fig. 1C strongly resemble those found in lignocellulosic structures. Notably, the ~1 nm spacing is within range of crystalline cellulose lattice spacing in terrestrial plants. Furthermore, the Ryugu matrix includes carbonates and magnetite, which on Earth often accompany fossilized biological remains. The morphological match does not prove biogenicity but significantly strengthens the case for fossilization.

The schematic and TEM analogs (Fig. 2) emphasize the plausibility that Ryugu’s structures are not random intergrowths but represent preserved biological features. This invites further geochemical and isotopic investigation to confirm the biological or prebiotic origin of these intriguing nanostructures.

Conclusion

Figure 1C from the Ryugu C0068 sample reveals lattice-scale features consistent with the periodic lamellae of secondary wood cell walls. Comparative analysis with terrestrial wood tissue (Fig. 2) supports the interpretation that such features may be of biogenic origin, representing either fossilized remains or complex prebiotic architectures.

References

1. Nakamura, T. et al. (2022). Formation and alteration history of the C-type asteroid Ryugu: Direct evidence from returned samples. *Science*, 379(6629), eabn8671. https://doi.org/10.1126/science.abn8671
2. Singh, A. P. et al. (2002). Structure and function of lignin in plants. *Annals of Botany*, 90(3), 301–311.
3. Donaldson, L. (2007). Cell wall structure of tracheids in Pinus radiata. *IAWA Journal*, 28(2), 173–184.

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