Science Tips Tips Tricks Technology Pluto was once hot and harbors oceans today, study finds

Pictures from NASA’s New Horizons space probe confirm that Pluto harbors an ocean beneath its thick, icy shell, researchers report in a new study. 

Contrary to the original “cold start” belief that Pluto was once a block of ice that has warmed through radioactive decay, experts now believe the planet was once hot and contained early oceans that are still present today. 

Pluto, an icy dwarf planet half the size of the United States, is in the Kuiper Belt about 3.6 billion miles away from the sun. It has a methane, nitrogen and carbon monoxide atmosphere. Pluto’s surface temperature of minus-378 to minus-396 degrees is too cold to sustain life, according to NASA.

New Horizons, launched in 2006, was the only spacecraft to visit Pluto. It sailed by the distant planet in 2015. 

“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,” Francis Nimmo, professor of Earth and planetary sciences at the University of California-Santa Cruz, said 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.”

Along with Pluto, other large Kuiper Belt objects, such as dwarf planets Eris and Makemake, are thought to have had “hot starts.”

“Even in this cold environment so far from the sun, all these worlds might have formed fast and hot, with liquid oceans,” Carver Bierson, the study’s lead author and UCSC graduate student, said in a statement. 

Shifting tectonics created varying surface textures overtime that allowed experts to recognize whether the ice was melting or freezing and when, which provided a timeline of Pluto’s surface changes, Bierson said. 

“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,” Bierson said.

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

Research such as NH3 (ammonia) sample collections and monitoring of ice thickness has shown that clues to Pluto’s extension outweighs evidence of a compression.

“How Pluto was put together in the first place matters a lot for its thermal evolution,” Nimmo said. “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.”

Pluto would have needed energy for its presumed rapid heating. The main potential energy sources that could have produced Pluto’s “hot start” are speculated to be gravitational energy released at the time of rapid accretion and heat released through radioactive decay of elements, according to experts. 

The new research was published this week in the peer-reviewed British journal Nature Geoscience.

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