Artist's conception of clouds in Pluto's atmosphere. (Photo by: Photo 12/Universal Images Group via Getty Images)


Artist's conception of clouds in Pluto's atmosphere. (Photo by: Photo 12/Universal Images Group via Getty Images)

The Secret of Pluto’s Ocean

When we think of an ocean, we don't necessarily think of Pluto. If we can’t see the liquid water, why do astronomers think it’s there?

February 18, 2020

When we think of water on a planet, our minds go to certain images: waves lapping at a sandy beach, a thundering waterfall, and meandering brook. You know, the familiar liquid sites here on Earth, where water is abundant on the surface.

While our home planet is indeed the only known world to host liquid water on its surface, it’s not the only place in the solar system where you can slap on a swimsuit and take a dip.

And perhaps the most unlikely place to host an ocean of liquid water? Tiny little Pluto, a world not even as big as our Moon, clinging to the frozen fringes of our solar system like an unwanted runt of the litter.

Water? On Pluto? We have pictures of Pluto thanks to the historic New Horizons flyby in 2015. We saw many wondrous and mysterious things: nitrogen ice glaciers, water ice mountains, and a thin atmosphere. But we didn’t see any water. So where is it?

Pluto’s ocean, like the rest of the liquid water in the solar system, is hidden, a secret buried under miles of rock-hard ice. But if we can’t see it, why do astronomers think it’s there?

A scene on Pluto with Charon, its giant moon.


A scene on Pluto with Charon, its giant moon.

Photo by: Ron Miller

Ron Miller

For one, Pluto has a healthy fraction of radioactive elements inside of it. These elements decay over time, releasing heat. Similar elements inside the Earth generate enough heat to turn rock into magma. So out there on the edge of the solar system, it’s not a stretch to imagine the heat turning ice into water.

Second, the nitrogen glaciers. The surface of Pluto has a giant, gaping wound called the Sputnik Planitia, home to a network of slow-moving interlocking glaciers. Something is keeping those glaciers churning and the likely culprit is heat escaping the core – the same heat that might liquify water deeper down. And our best guess as to how it formed in the first place? Astronomers suspect something large smashed into Pluto long ago, causing water to gush out and seep over the surface – a lesion that never quite healed.

Lastly, there are curious features all over the face of Pluto, subtle cracks and fissures that are the telltale signs of tectonic activities. These are the same kinds of rifts and mountain chains you might find on the Earth. In the outer solar system, usually gravitational interactions are responsible for such shifts in a crust, but Pluto has nothing big enough nearby to cause that kind of stress.

But if it had a liquid water ocean that was slowly cooling – but not yet completely frozen – the expansion of that water as it turned to ice would pop and crack the crust, causing the features that we see.

It’s not a slam-dunk case. We’re not as confident about water inside Pluto as we are on, say, Europa or Enceladus. But it’s an intriguing set of clues that point to an ocean completely encircling the little world to a depth of over a hundred miles. In other words, more liquid water than the Earth has.

So on the next mission to Pluto, you better pack the scuba gear.

#TeamPluto premieres Tuesday, February 18th at 11pm ET/PT on Discovery and Discovery Go.

Paul M. Sutter

Paul M. Sutter is an astrophysicist at Stony Brook University and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of How to Die in Space.

Next Up

SpaceX vs. the Universe

Fans of space are having a tough time picking sides over a recent controversy between SpaceX and astronomers. But what's the big debate all about? Astrophysicist Paul M. Sutter digs into both perspectives.

All Aboard the Starliner!

Boeing’s Starliner capsule launched on Friday. Astrophysicist Paul M Sutter has everything you need to know about the Starliner and its mission.

Let’s Look for Water on the Moon

NASA is headed to the moon, but this time it's in search of water. Astrophysicist Paul M Sutter shares what this means and why it's important.

The Perseid Meteor Shower Reaches its Peak

Stargazers rejoice! The annual Perseid meteor shower is upon us. Here's what you need to know...(updated August 11, 2022)

The 2020 Planetary Primaries

What’s your favorite planet? Before you decide, here are some key facts about each of the candidates.

Check Out the Crab Nebula –The Leftovers from a Giant Cosmic Firework

The Crab Nebula sits 6,500 light-years away, and is currently about 11 light-years across. But while it looks pretty from afar, don’t give in to the temptation to visit it up close.

How Did the Solar System Form?

How did our solar system form? It's a pretty simple and straightforward question, but as with most things in science, simple and straightforward doesn't necessarily mean easy.

Welcome to the Surface of Mars

Through the use of cutting-edge instruments, scientists finally have the opportunity to probe deep beneath the surface and ascertain exactly how the terrestrial planet formed.

The Kuiper Belt: When Solar Systems Dance

Pluto isn't alone after all. Besides being the home of Pluto, the Kuiper belt hosts dwarf planets, and smaller bits of rock and ice.

Last Call for the King of Planets

This month Jupiter is entering conjunction which means it's the last chance this year to catch a glimpse of the largest planet in our solar system.

Related To: