10:45 AM - 11:00 AM
[PPS07-07] Co-evolution of minerals and organics during aqueous alteration on planetesimals: Hydrothermal experiments using amorphous enstatite
Keywords:aqueous alteration, amorphous silicate, organic matter, Ryugu
Extraterrestrial organic matter is expected to provide insights into the prebiotic chemistry and the birth and evolution of the Solar System. Ryugu samples and carbonaceous chondrites contain insoluble organic matter (IOM) (e.g., Yabuta et al., 2023) and solvent-soluble organic molecules (SOM), including prebiotic molecules (e.g., Koga and Naraoka, 2017; Furukawa et al., 2019; Naraoka et al., 2023; Oba et al., 2023; Takano et al., 2024; Glavin, Dworkin et al., 2025). Carbonaceous chondrites and returned asteroid samples have often undergone aqueous alteration on their parent bodies, leading to the synthesis, destruction, and evolution of organic matter.
Laboratory experiments simulating organic matter formation during aqueous alteration have been conducted. Hydrothermal synthesis from formaldehyde and ammonia produces IOM analogues and amino acids found in meteorites (Cody et al., 2011; Kebukawa et al., 2017; Koga and Naraoka, 2017). Organic matter may interact with minerals during aqueous alteration (De Gregorio and Engrand, 2024), and experiments with phyllosilicates and olivine showed that coexisting minerals affect organic evolution (Vinogradoff et al., 2020; Hirakawa et al., 2021). However, since phyllosilicates formed via aqueous alteration (e.g., Nakamura et al., 2022) and olivine survived it (e.g., Kawasaki et al., 2022), they may not be suitable for studying the co-evolution of minerals and organics.
Observations of protoplanetary disks and analyses of primitive meteorites and returned samples suggest that the original dust in protoplanetary disks consists of amorphous silicates. In this study, hydrothermal experiments using amorphous enstatite were conducted to understand the co-evolution of minerals and organic matter.
Amorphous enstatite, formaldehyde, glycolaldehyde, hexamethylenetetramine (HMT), and ultrapure water were used as starting materials (e.g., Cody et al., 2011; Kebukawa et al., 2017; Isono et al., 2019). These were mixed to match Ryugu’s carbon and nitrogen abundances (Yokoyama et al., 2022; Naraoka et al., 2023; Oba et al., 2023). The starting materials were sealed in glass tubes and heated at 90°C for 2–3 weeks.
The bulk solid phase of experimental product was examined by X-ray diffraction (XRD) and infrared (IR) spectroscopy. Soluble organic matter was analyzed with high-resolution Orbitrap mass spectrometry, and solid organic matter was characterized via thermal decomposition gas analysis in vacuum.
Mg-silicate hydrate formed in the samples with W/R of 1 and 4, as confirmed by XRD and IR. CHO and CHNO compounds dominated the soluble organic matter, with CHNO abundance increasing in the samples containing HMT. Several (CH2O)n molecules were detected, indicating sugar formation via formose reactions. In the samples with W/R of 1, sugar related molecules were less abundant than in the samples with W/R of 0, suggesting that water promoted formose reaction, bypassing SOM and forming more complex IOM. Additionally, sugar related molecules were less abundant in the samples with initial HMT, suggesting Maillard reaction between N-fragments from HMT and CHO molecules. Analyses of released gases from solid organic matter also showed that water promoted formose reaction and new N-compounds were formed from HMT.
The present experiments did not well reproduce the phyllosilicates, O-poor soluble organic matter, and complex solid organic matter in Ryugu, indicating that higher temperature, longer reaction duration, and/or more reducing organic materials are needed to reproduce the chemical evolution in Ryugu.
We will conduct experiments with different heating conditions to verify the effects of water and HMT on organic matter synthesis. We also plan to explore conditions for reproducing the chemical evolution in Ryugu, for example by using more reduced organic matter than aldehydes as starting materials.
Laboratory experiments simulating organic matter formation during aqueous alteration have been conducted. Hydrothermal synthesis from formaldehyde and ammonia produces IOM analogues and amino acids found in meteorites (Cody et al., 2011; Kebukawa et al., 2017; Koga and Naraoka, 2017). Organic matter may interact with minerals during aqueous alteration (De Gregorio and Engrand, 2024), and experiments with phyllosilicates and olivine showed that coexisting minerals affect organic evolution (Vinogradoff et al., 2020; Hirakawa et al., 2021). However, since phyllosilicates formed via aqueous alteration (e.g., Nakamura et al., 2022) and olivine survived it (e.g., Kawasaki et al., 2022), they may not be suitable for studying the co-evolution of minerals and organics.
Observations of protoplanetary disks and analyses of primitive meteorites and returned samples suggest that the original dust in protoplanetary disks consists of amorphous silicates. In this study, hydrothermal experiments using amorphous enstatite were conducted to understand the co-evolution of minerals and organic matter.
Amorphous enstatite, formaldehyde, glycolaldehyde, hexamethylenetetramine (HMT), and ultrapure water were used as starting materials (e.g., Cody et al., 2011; Kebukawa et al., 2017; Isono et al., 2019). These were mixed to match Ryugu’s carbon and nitrogen abundances (Yokoyama et al., 2022; Naraoka et al., 2023; Oba et al., 2023). The starting materials were sealed in glass tubes and heated at 90°C for 2–3 weeks.
The bulk solid phase of experimental product was examined by X-ray diffraction (XRD) and infrared (IR) spectroscopy. Soluble organic matter was analyzed with high-resolution Orbitrap mass spectrometry, and solid organic matter was characterized via thermal decomposition gas analysis in vacuum.
Mg-silicate hydrate formed in the samples with W/R of 1 and 4, as confirmed by XRD and IR. CHO and CHNO compounds dominated the soluble organic matter, with CHNO abundance increasing in the samples containing HMT. Several (CH2O)n molecules were detected, indicating sugar formation via formose reactions. In the samples with W/R of 1, sugar related molecules were less abundant than in the samples with W/R of 0, suggesting that water promoted formose reaction, bypassing SOM and forming more complex IOM. Additionally, sugar related molecules were less abundant in the samples with initial HMT, suggesting Maillard reaction between N-fragments from HMT and CHO molecules. Analyses of released gases from solid organic matter also showed that water promoted formose reaction and new N-compounds were formed from HMT.
The present experiments did not well reproduce the phyllosilicates, O-poor soluble organic matter, and complex solid organic matter in Ryugu, indicating that higher temperature, longer reaction duration, and/or more reducing organic materials are needed to reproduce the chemical evolution in Ryugu.
We will conduct experiments with different heating conditions to verify the effects of water and HMT on organic matter synthesis. We also plan to explore conditions for reproducing the chemical evolution in Ryugu, for example by using more reduced organic matter than aldehydes as starting materials.