AUTHOR=Gobrecht David 

TITLE=Condensation sequence of circumstellar cluster seeds (CSCCS)

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=Volume 12 - 2025

YEAR=2025

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2025.1632593

DOI=10.3389/fspas.2025.1632593

ISSN=2296-987X

ABSTRACT=IntroductionTraditionally, the condensation sequence of circumstellar dust is predicted based on the thermodynamic stabilities of specific condensates in the macroscopic bulk phase. However, at the (sub-) nanometer scale clusters with non-crystalline structures and significantly different properties are energetically favoured.MethodsFor this reason, we study the thermodynamic stabilities of metal oxide clusters with generic stoichiometries of M2O3 and M3O4, where M represents a metal atom. With an upper size limit of 50 atoms, we consider clusters with sizes n = 1–10 for (M2O3)n, and n = 1–7 for (M3O4)n. The M2O3 clusters comprise alumina (Al2O3), Mg-rich pyroxene (MgSiO3) and a size-limited sample of titanates (CaTiO3), whereas the M3O4 clusters include spinel (MgAl2O4), Mg-rich olivine (Mg2SiO4) and calcium aluminates (CaAl2O4).ResultsWe find that, apart from the alumina monomer, the aluminum-bearing clusters (Al2O3)n, n = 1–10, and (MgAl2O4)n, n = 1–7, are favoured over their silicate counterparts (MgSiO3)n, n = 1–10 and (Mg2SiO4)n, n = 1–7. Also, we find that calcium aluminate clusters, CaAl2O4, are energetically more favourable than magnesium aluminate clusters, MgAl2O4. Furthermore, for a limited data set of (CaTiO3)n, n = 1–2, clusters we find significantly larger stabilities than for the other considered (M2O3)n clusters, namely Al2O3 and MgSiO3.DiscussionFuture investigations, in particular on titanates and on Ca-rich silicates, are required to draw a more thorough and complete picture of the condensation sequence at the (sub-)nanoscale.