  In the Solar System short-lived radioisotopes, such as 26Al, played a crucial
role during the formation 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 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 shortlived radionuclides upon planetesimal
formation from white dwarf data. We argue that the current evidence from white
dwarfs point towards a significant fraction of exo-planetesimals having formed
an iron core. Although the data may be explained by the accretion of exo-moon
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 rare chance encounters with single nearby
supernovae, Wolf-Rayet or AGB stars.
