240-7 Characterizing the Mechanical Properties of Insoluble Organic Matter with Nanoindentation: Implications for Planet Formation and Tidal Heating in Icy Bodies

Session: From Atoms to Asteroids and Habitable Planets: Coordinated Analysis of Planetary Samples and Their Terrestrial Analogues

Presenting Author:

Eric Austin

Authors:

Austin, Eric Clifton¹, Yu, Xinting², Husic, Adis³, Foustoukos, Dionysis⁴, Miller, Kelly⁵, Alexander, Conel⁶, Whittington, Alan⁷, Glein, Christopher⁸, Truong, Ngoc Tuan⁹, Vega, Ricardo¹⁰

(1) Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA, (2) Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA, (3) Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA, (4) Earth and Planets Lab, Carnegie Science Institute, Washington, DC, USA, (5) Southwest Research Institute, San Antonio, TX, USA, (6) Earth and Planets Lab, Carnegie Science Institute, Washington, DC, USA, (7) Earth and Planetary Science, University of Texas at San Antonio, San Antonio, TX, USA, (8) Southwest Research Institute, San Antonio, TX, USA, (9) Goddard NASA Space Flight Center, Greenbelt, MD, USA, (10) Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA,

Abstract:

Organic molecules are essential building blocks in the Solar System, but their precise role in planetary formation and the thermal evolution of icy bodies remains poorly understood, in part due to limited data on their physical properties. It is suggested that organics could coat silicate grains, increasing their ability to stick together and form planetesimals, and might also affect the internal heat and dynamics of icy moons. To address these uncertainties, this study characterized two key physical properties, Young's modulus and density, of Insoluble Organic Matter from chondrites (CIOM), the most common organic material found in meteorites.

Using nanoindentation, we measured the stiffness of CIOM from three different carbonaceous chondrites (Murchison, Tarda, and GRO 95577) that experienced varying degrees of aqueous alteration. These measurements were compared with synthetic organic analogs representing different formation processes, including ice irradiation, aqueous alteration, and gas irradiation.

The results revealed that CIOM has an intermediate stiffness (Y ≈ 2-6 GPa), which is an order of magnitude stiffer than residues from ice irradiation (Y ≈ 0. 0.1 GPa) but more flexible than analogs from gas irradiation (~10 GPa). This intermediate stiffness indicates a complex, multi-stage origin, likely involving the formation of precursors in cold environments, followed by subsequent processing that stiffened the macromolecules. The CIOM from the most primitive meteorite (GRO 95577) was found to be mechanically softer than the others, suggesting that aqueous alteration on a parent body can increase CIOM's stiffness. Density measurements of synthetic IOM matched terrestrial analogs currently used in planetary models.

Furthermore, the measured Young's modulus for CIOM is much lower than that of silicates (>50 GPa) and water ice (~10 GPa), indicating it is considerably more flexible. This has two main implications: first, increased elasticity could improve the sticking efficiency of dust grains, helping to overcome fragmentation barriers and speeding up planetesimal growth; second, in icy worlds, an organic- rich interior would deform more easily under tidal forces, leading to enhanced tidal heating and affecting the body's thermal evolution and potential habitability.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7198

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