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Scientists Finally Figured Out Why Pluto Has That Icy Heart

The dwarf planet’s geography, atmosphere and chemistry helped form its most famous feature

The forces that formed Pluto's heart may not be romantic, but the feature was love at first sight for scientists. (NASA/JHUAPL/SwRI)
smithsonian.com

Before New Horizons buzzed by Pluto this summer, scientists had no idea what the dwarf planet really looked like. As the craft hurtled closer and closer to the once-mysterious world, they spotted a puzzling heart-shaped mark on its surface. It was love at first sight. Now, reports Sid Perkins for Science, the heart’s true origins have finally come into focus—and though they're not very romantic, they're as fascinating as the heart itself.

The heart-shaped feature is called the Tombaugh Regio and is located slightly north of Pluto’s equator. The dwarf planet's brightest feature, researchers couldn’t help but spot it soon after New Horizons began its flyby in July. They quickly realized that at least part of the heart consists of an icy, frozen plain studded with mysterious moving hills formed by glaciers and flowing ice—a hint that geological activity is still going on beneath Pluto’s chilly surface.

In a new paper in the journal Nature, researchers revealed how Pluto may have gotten those glaciers. They used atmospheric models to go back in time, recreating the last 50,000 years of the dwarf planet's evolution. Researchers hypothesized that there was some kind of underground source that spewed out its primarily nitrogen-based ice—likely fueled by a massive underground ocean. But when they played out a simulation of how the dwarf planet must have evolved, they found something quite different.

As Perkins explains, if the model didn’t include any geological features it would be easy to predict how Pluto would react as it orbited around the sun 200 times, or over 50,000 years. As the dwarf planet rotated, its thin ice would migrate either toward the equator or the poles. That’s not what happened on Pluto, of course: It has northern frosts and a heart-shaped feature slightly north of its equator, but no permanent band of ice.

When the team added in Pluto’s topographic features, however, they learned that basins and indentations like the Sputnik Planum, which is nearly 2.5 miles deep, actually trapped many of the dwarf planet’s elements, like methane, nitrogen and carbon monoxide. This jives with what scientists know about the dwarf planet—since Pluto doesn’t have much of an atmosphere, it makes sense that it would only be able to hold onto ice that’s located in low elevations, like basins.

Now that the origin of Pluto’s big heart is clear, scientists hope to use their discovery to predict how it will act in the future. It looks like seasonal frosts will fade over time as the atmospheric pressure that makes frost cling to Pluto’s surface drops. Don’t worry—as co-author Tanguy Bertrand tells Gizmodo’s Ria Misra, the heart won’t go away, just migrate back and forth a little. Its origins may not be that romantic, but there’s something to be said for a heart that simply can’t be stopped.

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