Evidence of a secret ocean inside Pluto makes extraterrestrial life more plausible

pluto
CC BY 2.0 Natural color images of Pluto taken by NASA's New Horizons spacecraft in 2015. (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker)

Scientists think there is a a hidden, protected ocean inside of Pluto – and the implications are wild.

In July 2015, after almost 10 years of traveling, NASA’s piano-sized New Horizons spacecraft zipped by Pluto and took loads of photos to the delight of scientists back on the mothership Earth. WIth the first-ever close-up images of everybody's favorite little dwarf planet and her moons, all kinds of discoveries have been and continue to be made.

Among other things, the photos showed Pluto’s unexpected topography, including a bright, Texas-sized basin named Sputnik Planitia.

When studying the images and data, scientists thought that a subsurface ocean seemed to exist beneath the ice shell which is thinned at Sputnik Planitia. There was just one problem with that theory: Because of the age of Pluto, the ocean would long be frozen and the inner surface of the ice shell facing the ocean should have been flatter than it appears.

PlutoFigures created using images by NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute./CC BY 2.0
Above: The bright “heart” on Pluto is located near the equator. Its left half is a big basin dubbed Sputnik Planitia.

Now, however, researchers have found compelling evidence that an "insulating layer" of gas hydrates could keep a subsurface ocean from freezing beneath Pluto’s icy exterior, according to Hokkaido University in Japan.

The researchers – from Hokkaido University, the Tokyo Institute of Technology, Tokushima University, Osaka University, Kobe University, and at the University of California, Santa Cruz – wondered what could be keeping this suspected subsurface ocean warm, while also keeping the ice shell’s inner surface frozen and uneven. They came up with the idea that a layer of gas hydrates exists underneath the ice of Sputnik Planitia.

"Gas hydrates are crystalline ice-like solids formed of gas trapped within molecular water cages," explains Hokkaido. "They are highly viscous, have low thermal conductivity, and could therefore provide insulating properties." In the most simple analogy, I see this like some kind of (much-more-complicated) bubble wrap over a pool in the winter.

plutoKamata S. et al., Pluto's ocean is capped and insulated by gas hydrates. Nature Geosciences, May 20, 2019./CC BY 2.0
Above: The proposed interior structure of Pluto. A thin clathrate (gas) hydrate layer works as a thermal insulator between the subsurface ocean and the ice shell, keeping the ocean from freezing.

The team used computer simulations spanning the 4.6 billion years since the solar system began to form. They found that without a gas hydrate insulating layer, the subsurface sea would have frozen completely hundreds of millions of years ago; but with one, it hardly freezes at all.

They think that the gas within the insulating layer could be methane originating from Pluto’s rocky core. "This theory, in which methane is trapped as a gas hydrate," says Hokkaido, "is consistent with the unusual composition of Pluto’s atmosphere – methane-poor and nitrogen-rich."

The simulation results gave what the scientists are calling "compelling evidence" that a long-lived liquid ocean exists beneath Pluto's icy crust. And if such is the case, these gassy insulating layers on other celestial objects could mean there are more oceans out there than we imagined, which opens up even more possibilities.

“This could mean there are more oceans in the universe than previously thought, making the existence of extraterrestrial life more plausible,” says Shunichi Kamata of Hokkaido University who led the team.

It is a wild thing to consider, that on various orbs and objects across the universe there could be secret oceans, being kept warm by gassy layers and protected by covers of ice. And that these subsurface oceans could be thriving with life, hidden away from the prying eyes of piano-sized spaceships is a profound, yet strangely comforting, notion.

For much more on the science of the study, the paper, "Pluto’s ocean is capped and insulated by gas hydrates," was published in Nature Geoscience and can be seen here.

Evidence of a secret ocean inside Pluto makes extraterrestrial life more plausible
Scientists think there is a hidden, protected ocean inside of Pluto – and the implications are wild.

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