Galactic radioactive links to rocky worlds

The thermal evolution of rocky exoplanets is modulated by (i) left-over (gravitational) heat of accretion, and (ii) radiogenic heating from the decay of long-lived radioactive isotopes, particularly K, Th, U, and U. These heat-producing elements (HPEs) are synthesized through distinct nucleosynthetic pathways and evolved in both relative and absolute abundance over time as traced via galactic chemical evolution (GCE) – and where possible – direct or proxy spectroscopic observations. We synthesize current understanding of how GCE processes control the radiogenic heat budgets of rocky exoplanets by mapping HPEs across different stellar populations in the Milky Way. Combining GCE models with thermal evolution simulations reveals that planets forming around older, metal-poor stars possess significantly lower initial radiogenic heat inventories compared to younger, metal-rich systems. Depending on the HPE, initial radiogenic heat production in Earth-mass planets can vary by a factor of 2–10 between  different stellar environments. We explore how this variation impacts planetary geodynamics, magnetic dynamo generation, volcanic activity and secondary atmosphere outgassing, as well as biocompatibility. We present theoretical models showing that stagnant-lid rocky exoplanets around old stars may exhaust their radiogenic heat budgets within 2–4 Gyr, potentially entering Venus-like states and losing their capacity to maintain temperate climates through carbon cycling. Conversely, planets with enhanced HPE abundances may experience excessive radiogenic heating, leading to prolonged magma ocean phases, hyper-volcanism or dynamo failure. We identify a "metallicity Goldilocks zone" near solar values where persistent magnetic dynamos can be sustained. Our analysis demonstrates that the galactic context of planetary formation - encoded in stellar metallicity, age, and nucleosynthetic history of the HPEs - governs both long-term thermal evolution and an exoplanet’s biocompatibility.