Even though Pluto isn’t a planet anymore, it’s still a planetary body with a lot of heart. Well, at least one heart. When NASA’s New Horizons mission brought back pictures of Pluto in 2015, one of the most striking discoveries was a heart-shaped geographic feature that is nearly 1300 miles long. Officially named the Tombaugh Regio in 2015 after Clyde Tombaugh, who discovered the dwarf planet, the feature surprised scientists because its white color meant that something in its structure was reflecting an intense amount of light off of the surface.

Of special interest was the western part of the region, named the Sputnik Planitia. Scientists initially thought this part of the region was a plateau but soon realized that it was a large basin filled with nitrogen ice. Smoothed over the millennia, the nitrogen ice creates a brilliant surface. The eastern part is also covered in ice, just less of it so it doesn’t shine quite as much.

What accounts for these different lusters? According to a paper published by scientists at the University of Bern in 2024, Sputnik Planitia seems to have been formed by Pluto’s collision with a large object about twice the size of Switzerland. The elongated, heart shape suggests that the collision happened at an angle and at a relatively low velocity. According to the scientists, Pluto’s core is so cold and rigid that it didn’t melt or deform from the impact and in fact caused the whole object to “splat” on the surface rather than sink to the core of the planet. After all, affairs of the heart can be messy, even for planetary bodies!

Sources

How Pluto Got Its Heart University of Bern

Sputnik Planitia Nature Astronomy

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