<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Huang, Dongyang</style></author><author><style face="normal" font="default" size="100%">Caroline Dorn</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Limits on forming coreless terrestrial worlds in the TRAPPIST-1 system</style></title><secondary-title><style face="normal" font="default" size="100%">Monthly Notices of the Royal Astronomical Society</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">2026</style></year></dates><urls><web-urls><url><style face="normal" font="default" size="100%">https://academic.oup.com/mnras/article/550/2/stag1234/8719665</style></url></web-urls></urls><volume><style face="normal" font="default" size="100%">550</style></volume><pages><style face="normal" font="default" size="100%">stag1234</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">With seven temperate Earth-sized planets revolving around an ultracool red dwarf, the nearby TRAPPIST-1 system offers a unique opportunity to verify models of exoplanet composition, differentiation, and interior structure. In particular, the low bulk densities of the TRAPPIST-1 planets, compared to terrestrial planets in our Solar system, require either substantial amount of volatiles to be present or a core-free scenario where the metallic core is fully oxidized. Here, we test the validity of the core-free scenario given thermodynamic constraints. In particular, we update a metal–silicate partitioning model within the equilibrium differentiation framework. We show that during core–mantle differentiation, oxygen becomes more siderophile (iron-loving) with increasing pressure, implying larger planet radii. For the seven TRAPPIST-1 planets, however, we find that they are not sufficiently massive to oxidize all the iron in the core, if they differentiate from an Earth-like composition. Oxygen partitioning in rocky worlds thermodynamically precludes coreless planets up to 4 M⊕. The observed density deficit in the TRAPPIST-1 planets, and more generally in M dwarf systems if confirmed by future observations, may be explained by system-dependent element budgets during planet formation, which are intrinsically linked to their stellar metallicity.</style></abstract><issue><style face="normal" font="default" size="100%">2</style></issue></record></records></xml>