  Whilst the formation of Solar system planets is constrained by meteoritic
evidence, the geophysical history of low-mass exoplanets is much less clear.
The bulk composition and climate states of rocky exoplanets may vary
significantly based on the composition and properties of the planetesimals they
form from. An important factor influenced by planetesimal composition is water
content, where the desiccation of accreting planetesimals impacts the final
water content of the resultant planets. While the inner planets of the Solar
system are comparatively water-poor, recent observational evidence from
exoplanet bulk densities and planetary formation models suggest that rocky
exoplanets engulfed by substantial layers of high-pressure ices or massive
steam atmospheres could be widespread. Here we quantify variations in
planetesimal desiccation due to potential fractionation of the two short-lived
radioisotopes 26Al and 60Fe relevant for internal heating on planetary
formation timescales. We focus on how order of magnitude variations in 60Fe can
affect the water content of planetesimals, and how this may alter the formation
of extrasolar ocean worlds. We find that heating by 26Al is the dominant cause
of planetesimal heating in any Solar system analogue scenario, thus validating
previous works focussing only on this radioisotope. However, 60Fe can become
the primary heating source in the case of high levels of supernova enrichment
in massive star-forming regions. These diverging scenarios can affect the
formation pathways, bulk volatile budget, and climate diversity of low-mass
exoplanets.
