While the surface of Pluto is frigid today, its formation was likely to have been a hot, violent affair, according to a new study led by Carver Bierson of the University of California, Santa Cruz. If this is correct, it dramatically increases the chance that liquid water has been present under Pluto’s surface since its formation, making it potentially habitable for a longer period of time.

Bierson’s team determined Pluto’s heating history by examining its tectonic features. Extensional features, such as rift valleys or fractures, can form when water in a subsurface ocean freezes. Freezing increases the volume of water, forcing the ice above it to stretch. Conversely, when an ice shell melts, its volume decreases, and compressional tectonic features such as ridges are formed. According to previous models, Pluto formed from slowly coalescing particles that retained little heat from accretion. In this “cold start” scenario, a subsurface ocean would only form later in Pluto’s history as the ice shell melted due to heat from the decay of radioactive elements. However, Bierson and coauthors found very little evidence for the compressional terrains that would be predicted by the “cold start” model, even in the oldest parts of Pluto’s surface that have been imaged. They, therefore, concluded that Pluto accreted quickly in a “hot start” scenario, using the energy of rapid gravitational accretion and impacts to form a subsurface ocean very early in Pluto’s history. The rifts and fractures observed on the surface are the result of that ocean slowly cooling and freezing over time. Based on their model for Pluto’s formation, they also estimated that many other Kuiper Belt objects would have a similar formation path, implying that early subsurface oceans may have been a common feature of these distant, icy bodies. READ MORE