Does Pluto's heart have a pulse? Peculiar polygons suggest activity on dwarf planet

Pluto's distinctive heart-shaped feature may appear still, but it's actually made up of churning icy cells, scientists say.

Courtesy of NASA/JHUAPL/SwRI
Scientists from NASA’s New Horizons mission used state-of-the-art computer simulations to show that the surface of Pluto’s informally named Sputnik Planum is covered with churning ice "cells" that are geologically young and turning over due to a process called convection. The scene above, which is about 250 miles (400 kilometers) across, uses data from the New Horizons Ralph/Multispectral Visible Imaging Camera (MVIC), gathered July 14, 2015.

Pluto's bright "heart" captivated astronomers and amateurs alike when NASA's New Horizons spacecraft beamed back the first clear images of the dwarf planet last July. But there's more to that distinctive shape than meets the eye.

In particular, the left lobe of the heart-shaped feature, informally dubbed Sputnik Planum, appears unusually smooth and plain at a glance. But when scientists took a closer look, they spotted a strange rubbly pattern across the expanse. 

Interlocking polygons appear to be etched into the surface of Sputnik Planum, slightly elevated in their centers, making the bright plain look as if snakeskin had been stretched across it.

"It was such an unusual pattern to see at such a large scale," says William McKinnon, a co-investigator on the New Horizons team and researcher at Washington University in St. Louis. 

What's behind these strange shapes?

It turns out this part of Pluto's "heart" is actually a sort of cosmic lava lamp, according to models described in two different papers published Wednesday in the journal Nature. And the feature continues to churn, resurfacing the region on geologically short timescales.

Sputnik Planum is covered with a sheet of nitrogen ice. Heat produced by radioactivity in the rocky interior of Pluto causes the nitrogen at the bottom of this icy layer to expand, making it more buoyant. That heated nitrogen ice begins to rise. 

Once it has risen, the nitrogen ice begins to cool and sink back down. This cycle, called convection, forms cells. 

"All of these individual blobs you see in these pictures are the rising tops of these convection cells," Dr. McKinnon, lead author of one of the new studies, tells The Christian Science Monitor. "It's basically like a giant lava lamp."

And "not only is this material convecting," says Alexander Trowbridge, lead author of the other study, but "it's convecting vigorously."

In fact this process churns so rapidly that Pluto's heart gets a full face-lift every 500,000 to 1 million years or so. "It's solid material in motion," McKinnon says.

This process could explain why Sputnik Planum is so remarkably smooth. "The whole ice sheet has not a single crater on it," Mr. Trowbridge, a PhD student at Purdue University, tells the Monitor. 

"Crater counting in planetary science is used to determine the ages of surfaces," Trowbridge says. A surface that isn't pockmarked with impact craters means it hasn't been around very long to be hit by space rocks.

"Because there are no craters in this area, it puts a maximum age at 10 million years for this surface, which is incredibly young for the surface of Pluto," Trowbridge says.

And convection makes the smoothness of Pluto's heart less mysterious, says Geoffrey Collins, a planetary geologist at Wheaton College in Norton, Mass. who was not part of either study. "If you have this convective process, you can erase the impact craters continuously," he tells the Monitor.

Cracking the case on convection

Scientists have been abuzz about the strange cellular structures appearing on Sputnik Planum "ever since those first pictures came back last summer," Dr. Collins says. 

"Convection popped up as one of the first explanations," he says, but it wasn't the only one. Some suggested that the surface could have cracked under temperature pressures, or perhaps ice wedging could explain the odd polygons.

"But none of those really work in a big nitrogen-ice dominated basin," Collins says. So when the spectrometer data from New Horizons confirmed that Sputnik Planum is filled with nitrogen ice, the convection model "seemed to fit."

Now McKinnon and colleagues have created a computer simulation of how that process works. And both teams calculated the Rayleigh number, a parameter associated with buoyancy-driven flow that determines whether heat travels through a material by way of convection or conduction. 

Trowbridge and his team also ruled out any sort of brittle cracking, as it wouldn't resurface Pluto's heart on the timescales necessary to make it so smooth.

Both teams confirm that convection explains Pluto's polygons.

"These two papers are written by two completely different sets of people. One of whom is deeply involved in the New Horizons team and the other is a group that's outside the team," Collins says. "If you wanted to have some kind of scientific fight, that's the perfect set up. And yet the two groups reach essentially the same conclusion."

Taking the pulse of Pluto

Discovering dynamic processes like convection on the icy surface of Pluto "validates why you send these missions in the first place," Trowbridge says of the New Horizons mission, of which he was not affiliated. "They're writing the book on Pluto right now."

And these discoveries display "the richness and variety of nature," McKinnon says. 

"We can fly to the edge of the solar system," he says. "We can fly past Neptune to a distant, small planet, and instead of finding a cold, dead world covered in craters, we find this wildly active place."

You've read  of  free articles. Subscribe to continue.
Real news can be honest, hopeful, credible, constructive.
What is the Monitor difference? Tackling the tough headlines – with humanity. Listening to sources – with respect. Seeing the story that others are missing by reporting what so often gets overlooked: the values that connect us. That’s Monitor reporting – news that changes how you see the world.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to

QR Code to Does Pluto's heart have a pulse? Peculiar polygons suggest activity on dwarf planet
Read this article in
QR Code to Subscription page
Start your subscription today