Experimental study on troilite evaporation to constrain condensation processes from the solar nebula

Chondritic meteorites are the most pristine materials in our Solar System, reflecting the earliest stages in the development of a protoplanetary disk. Their components are the results of condensation of nebular gases during the cooling phase of the solar nebula. Condensation models which consider equilibrium processes have been able to successfully predict the general mineralogy of chondrites, but struggled to reproduce the specific groups of chondrites – enstatite, ordinary, and carbonaceous chondrites. Recently, a condensation model which involves non-equilibrium processes predicted the formation of the individual chondrite groups [1]. However, quantitative data of the associated reactions, such as reaction rates and evaporation kinetics, is lacking. We aim to provide numerical constraints needed to further develop models to simulate the early stages of the Solar System.

New observations from the James Webb Space Telescope (JWST) show evidence of early condensation and associated gases in the nebula around the protostar HOPS-315 [2], representing similar processes as in the Solar System billions of years ago. Specifically, they observe forsterite, enstatite, and gaseous SiO, suggesting ongoing condensation at high temperatures. The temperature at which forsterite and enstatite, as well as Fe-Ni metal, condense (~1300-1400 K) is considered as the boundary between refractory and moderately volatile elements [3]. At lower temperatures, condensation of troilite (FeS) at ~670 K defines the boundary between moderately volatile and highly volatile elements [3]. Troilite is also the phase in which sulfur first condenses after reacting with Fe metal [4]. Sulfur plays an important role in cosmochemistry, since it is the second most abundant volatile in chondrites and the tenth most abundant element in the universe. Hence, constraining the properties of troilite condensation will improve current models describing the development of the Solar System. Because evaporation and condensation are reverse processes, evaporation kinetics can be used to infer condensation kinetics [5]. This approach can also be used to derive the activation energy of the reaction, which provides insights regarding the timescales involved in the cooling of the solar nebula.

In the ELMO (Experimental Laboratory Magma Ocean) group, we conduct evaporation experiments on silicates and sulfides using a NETZSCH Simultaneous Thermal Analyzer (STA) 449 F3 Jupiter [6,7]. The graphite furnace allows temperatures of up to 2000 °C in a high-vacuum environment. The sample carrier, which holds the graphite crucible containing the sample and measures the temperature via a type W thermocouple, is connected to a microbalance to track changes in the sample mass during heating. The sample chamber is also directly coupled to a quadrupole mass spectrometer (QMS) which is capable of measuring volatile species in the mass range of 1-512 amu. Hence, we are able to detect all potentially released gas species, such as S₂, CS₂, Fe, and FeS. Using this setup, we obtain in situ measurements to constrain evaporation kinetics and activation energies of the associated chemical reactions for the first time, as well as characterize the volatile species released during heating. Here, we present the results of the troilite evaporation experiments and its implications for the low-temperature stage of the cooling of the solar nebula.

[1] Charnoz et al. (2026). Nature, 652(8111), 925-930. [2] McClure et al. (2025). Nature, 643(8072), 649-653. [3] Larimer (1988). In: Meteorites and the Early Solar System, 375-389. [4] Larimer (1967). Geochimica et Cosmochimica Acta, 31(8), 1215-1238. [5] Hashimoto (1990). Nature, 347(6288), 53-55. [6] Renggli et al. (2026). Europlanet Science Congress 2026, EPSC2026-148. [7] Abel & Renggli (2026). Europlanet Science Congress 2026, EPSC2026-108.