Dwarf Pluto Likely Started Out as a Warm Planet With Vast Oceans

Pluto, as well as other larger Kuiper Belt Objects likely started out having vast liquid oceans.

Until now, and mostly due to its location so far from the Sun, scientists thought that the origin of the dwarf planet must have been very cold. However, new analyzes of the New Horizons spacecraft’s data seem to indicate the contrary that Pluto started as a warm planet and with oceans.

According to a study published in Nature Geosciences by a team of researchers at the University of California at Santa Cruz, who explains that Pluto may have had a “hot origin.”

According to scientists, the accumulation of new materials during the formation of the planet could, in effect, have generated enough heat to create, almost from the beginning, a large ocean of liquid water capable of lasting to this day under the icy crust, even despite the remoteness from the Sun.

People have long questioned Pluto’s thermal evolution and the underground ocean’s ability to survive to this day. Now that we have images of Pluto’s surface from NASA’s New Horizons mission, we can compare what we see with what different models of thermal evolution predict,” explained Francis Nimmo, co-author of the study.

According to Carver Bierson, the lead author of the new study, since water expands when it freezes and contracts when it melts, the different hot or cold formation scenarios have different implications for tectonics and the characteristics of the resulting surface of Pluto.

If Pluto started cold and the ice melted internally, Pluto would have contracted, and we should see compression characteristics on its surface. In contrast, if it started to warm, it should have expanded as the ocean froze. We should see extension characteristics on the surface, Bierson explains.

We see many expansion evidence, but we don’t see evidence of compression, so the observations are more consistent with Pluto starting with a liquid ocean.

But if Pluto had a warm origin, where did the energy for it come from? The researchers explain that the two main sources of energy would be, on the one hand, the heat released by the decomposition of radioactive elements within the rocks. On the other, the gravitational energy released as new materials bombarded the protoplanet’s surface in the distant times of its formation and growth.

Extensional faults (arrows) on the surface of Pluto indicate expansion of the dwarf planet’s icy crust, attributed to freezing of a subsurface ocean. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker).
Extensional faults (arrows) on Pluto’s surface indicate expansion of the dwarf planet’s icy crust, attributed to the freezing of a subsurface ocean. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker).

Bierson’s calculations show that if all gravitational energy had been retained as heat inside the planet, that energy would inevitably create an initial liquid ocean. However, if the accumulation of new material had occurred slowly, much of that energy would have been radiated away from the surface.

How Pluto formed in the first place is very important to its thermal evolution. If the hot material had accumulated very slowly, it would have radiated a lot of energy into space. But if it had built up fast enough, the heat would have been trapped inside, explained Bierson.

The researchers calculated that if Pluto formed over a period of fewer than 30,000 years, then its origin was hot. On the other hand, the accumulation of material that formed the planet took place over several million years. The hot origin would have been much more difficult.

The new findings imply that other large objects in the Kuiper Belt may also have had a similar start.

This means that many of them, like Pluto, could have early oceans, and that on larger objects, such as the dwarf planets Eris and Makemake, those oceans may have persisted to this day.

UC Santa Cruz


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