Prevalence of short-lived radioactive isotopes across exoplanetary systems inferred from polluted white dwarfs

In the Solar system, short-lived radioisotopes, such as 26Al, played a crucial role during the formation of planetary bodies by
providing a significant additional source of heat. Notably, this led to early and large-scale melting and iron core formation in
planetesimals and their loss of volatile elements, such as hydrogen and carbon. In the context of exoplanetary systems therefore
the prevalence of short-lived radioisotopes is key to interpreting the observed bulk volatile budget and atmospheric diversity
among low-mass exoplanets. White dwarfs that have accreted planetary material provide a unique means to infer the frequency
of iron core formation in extrasolar planetesimals, and hence the ubiquity of planetary systems forming with high short-lived
radioisotope abundances. Here, we devise a quantitative method to infer the fraction of planetary systems enriched with short-
lived radionuclides upon planetesimal formation from white dwarf data. We argue that the current evidence from white dwarfs
point towards a significant fraction of exoplanetesimals having formed an iron core. Although the data may be explained by
the accretion of exomoon or Pluto-sized bodies that were able to differentiate due to gravitational potential energy release, our
results suggest that the most likely explanation for the prevalence of differentiated material among polluted white dwarfs is
that the Solar system is not unusual in being enriched in 26Al. The models presented here suggest a ubiquitous pathway for
the enrichment of exoplanetary systems by short-lived radioisotopes, disfavouring short-lived radioisotope enrichment scenarios
relying on statistically rare chance encounters with single nearby supernovae, Wolf–Rayet, or AGB stars.
Key words: astrobiology – planets and satellites: atmospheres – planets and satellites: composition – planets and satellites:
formation – planetary systems – white dwarfs.