The Impact of Serpentinization on the Initial Conditions of Satellite Forming Collisions of Large Kuiper Belt Objects

Kuiper Belt objects are thought to be formed at least a few million years after the formation of calcium–aluminum-rich inclusions (CAIs), at a time when the 26Al isotope—the major source of radiogenic heat in the early solar system—had significantly depleted. The internal structure of these objects is highly dependent on any additional source that can produce extra heat in addition to that produced by the remaining, long-lasting radioactive isotopes. In this paper, we explore how serpentinization, the hydration of silicate minerals, can contribute to the heat budget and to what extent it can modify the internal structure of large Kuiper Belt objects. We find that the extent of restructuring depends very strongly on the start time of the formation process, the size of the object, and the starting ice-to-rock ratio. Serpentinization is able to restructure most of the interior of all objects in the whole size range (400–1200 km) and ice-to-rock ratio range investigated if the process starts early, ∼3 Myr after CAI formation, potentially leading to a predominantly serpentine core much earlier than previously thought (≤5 Myr versus several tens of million years). While the ratio of serpentinized material gradually decreases with the increasing formation time, the increasing ice-to-rock ratio, and the increasing start time of planetesimal formation in the outer solar system, in the case of the largest objects a significant part of the interior will be serpentinized even if the formation starts relatively late, ∼5 Myr after CAI formation. Therefore it is feasible that the interior of planetesimals may have contained a significant amount of serpentine, and in some cases, it could have been a dominant constituent, at the time of satellite-forming impacts.