Pluto is thought to possess a present-day ocean beneath a thick ice shell. It has generally been assumed that Pluto accreted from cold material and then later developed its ocean due to warming from radioactive decay; in this ‘cold start’ scenario, the ice shell would have experienced early compression and more recent extension. Here we compare thermal model simulations with geological observations from the New Horizons mission to suggest that Pluto was instead relatively hot when it formed, with an early subsurface ocean. Such a ‘hot start’ Pluto produces an early, rapid phase of extension, followed by a more prolonged extensional phase, which totals ~0.5% linear strain over the last 3.5 Gyr. The amount of second-phase extension is consistent with that inferred from extensional faults on Pluto; we suggest that an enigmatic ridge–trough system recently identified on Pluto is indicative of early extensional tectonics. A hot initial start can be achieved with the gravitational energy released during accretion if the final stage of Pluto’s accretion is rapid (<30 kyr). A fast final stage of growth is in agreement with models of the formation of Kuiper belt objects via gravitational collapse followed by pebble accretion, and implies that early oceans may have been common in the interiors of large Kuiper belt objects.

冥王星被认为在厚厚的冰壳下拥有当今的海洋。一般认为，冥王星从冷物质中吸出，然后由于放射性衰变而变暖，从而发展了海洋。在这种“冷启动”情况下，冰壳将经历早期压缩和最近的扩展。在这里，我们将热模型模拟与“新视野”任务的地质观测结果进行了比较，以表明冥王星形成时相对较热，且具有早期的地下海洋。这样的“热启动”冥王星会产生早期，快速的伸展阶段，然后是更长时间的伸展阶段，在最后的3.5 Gyr期间，其总线性应变约为0.5％。第二阶段扩展的数量与从冥王星上的扩展断层推断出的数量一致。我们认为，冥王星上最近发现的一个神秘的海槽系统可以指示早期的伸展构造。如果冥王星吸积的最后阶段很快（<30 kyr），则可以利用吸积期间释放的重力来实现热启动。快速增长的最后阶段与通过重力塌陷继而产生卵石堆积而形成柯伊伯带天体的模型相一致，这意味着早期的海洋可能在大型柯伊伯带天体的内部很普遍。