Deformation characteristics of solid-state benzene as a step towards understanding planetary geology

• Published in: Nature communications 2022-12, Vol.13 (1), p.7949-7949, Article 7949
• Main Authors: Zhang, Wenxin, Zhang, Xuan, Edwards, Bryce W., Zhong, Lei, Gao, Huajian, Malaska, Michael J., Hodyss, Robert, Greer, Julia R.
• Format: Article
• Language: English
• Subjects: 147/135; 147/143; 639/301/357/537; 639/925/930/12; Benzene; Canyons; Contact pressure; Cyclic loads; Deformation; Densification; Ethane; Geological processes; Geology; Geophysics; Humanities and Social Sciences; Hydrocarbons; Lunar surface; Mechanical properties; Microcrystals; Minerals; Molecular dynamics; multidisciplinary; Organic chemistry; Planetary geology; Plastic deformation; Pyramids; Saturn atmosphere; Science; Science (multidisciplinary); Shearing; Single crystals; Solar system; Solid state; Space missions; Stiffening; Stochasticity
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-35647-x

Small organic molecules, like ethane and benzene, are ubiquitous in the atmosphere and surface of Saturn’s largest moon Titan, forming plains, dunes, canyons, and other surface features. Understanding Titan’s dynamic geology and designing future landing missions requires sufficient knowledge of the mechanical characteristics of these solid-state organic minerals, which is currently lacking. To understand the deformation and mechanical properties of a representative solid organic material at space-relevant temperatures, we freeze liquid micro-droplets of benzene to form ~10 μm-tall single-crystalline pyramids and uniaxially compress them in situ. These micromechanical experiments reveal contact pressures decaying from ~2 to ~0.5 GPa after ~1 μm-reduction in pyramid height. The deformation occurs via a series of stochastic (~5-30 nm) displacement bursts, corresponding to densification and stiffening of the compressed material during cyclic loading to progressively higher loads. Molecular dynamics simulations reveal predominantly plastic deformation and densified region formation by the re-orientation and interplanar shear of benzene rings, providing a two-step stiffening mechanism. This work demonstrates the feasibility of in-situ cryogenic nanomechanical characterization of solid organics as a pathway to gain insights into the geophysics of planetary bodies. Solid benzene and other simple organic minerals play important roles in geological processes on Titan-like cold Solar System bodies. Here, the authors discover benzene microcrystals plastically deform via densification enabled by molecule reorientation and shearing.