Pluto was hot and already had an underground ocean shortly after its formation

Hyperaxion June 26, 2020 12:23 am

A new study suggests that Pluto may have had a “hot start” in the icy Kuiper Belt and developed an underground liquid ocean before previously thought.

American researchers came to this conclusion by comparing different thermal simulations of Pluto’s interior with observations of the dwarf planet by NASA’s New Horizons mission.

Pluto was hot and already had an underground ocean shortly after its formation
(Credit: New Horizons / NASA).

“For a long time people have thought about the thermal evolution of Pluto and the ability of an ocean to survive to the present day,” said Francis Nimmo, professor of Earth and Planetary Sciences at the University of California-Santa Cruz and co-author of the study, in a statement. “Now that we have images of Pluto’s surface from NASA’s New Horizons mission, we can compare what we see with the predictions of different thermal evolution models.”

Until 2015, when the NASA mission captured images of the dwarf planet, scientists knew little about its appearance. However, from the heart-shaped formation on Pluto’s surface to its icy volcanoes, the New Horizons mission showed that the planet was a geologically active object.

So, the suspicious underground salty ocean under Pluto’s icy shell was a particularly intriguing feature. Researchers traditionally attribute the formation of Pluto’s ocean to the heat generated by the radioactive decay inside the dwarf planet. However, the team’s new simulations showed that this “cold start” scenario would be insufficient to explain some of Pluto’s surface features seen by New Horizons.

“If it started cold and the ice melted internally, Pluto would have contracted and we should see compression features on its surface, whereas if it started hot it should have expanded as the ocean froze and we should see extension features on the surface,” explained lead author of the study, Carver Bierson. “We see lots of evidence of expansion, but we don’t see any evidence of compression.”

For Pluto to be hot enough to have a liquid ocean in its first days, a large majority of the gravitational energy released by the accumulated material must have been retained as heat. For that, its formation must also have happened quickly.

“How Pluto was put together in the first place matters a lot for its thermal evolution,” said Nimmo. “If it builds up too slowly, the hot material at the surface radiates energy into space, but if it builds up fast enough the heat gets trapped inside.”

From their calculations, the team shows that if the dwarf planet formed during a period of less than 30,000 years, the heat would be maintained.

This study was published this month in the scientific journal Nature Geoscience.

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