Pluto's Heart Is Actually Ice

When NASA's New Horizons spacecraft sped past Pluto in 2015, it revealed a world far more complex and dynamic than previously imagined. The most iconic feature to emerge from the blurry images of the past was a bright, continent-sized heart shape on its surface. This feature, named Tombaugh Regio after Pluto's discoverer Clyde Tombaugh, isn't just a superficial pattern. Its vast western lobe, Sputnik Planitia, is an enormous basin filled thousands of feet deep with frozen (Review) nitrogen, methane, and carbon monoxide ices.

This icy expanse is not static. Scientists were stunned to discover that it is geologically active. Faint heat from Pluto's interior causes the soft nitrogen ice to churn slowly in a process called convection, similar to the way wax circulates in a lava lamp. This constant, slow-motion churning renews the surface, erasing impact craters and creating a landscape of polygonal cells that is estimated to be less than 10 million years old—incredibly young for a planetary surface.

This giant frozen heart effectively acts as the engine for Pluto's climate. During the day, some of the nitrogen ice turns directly into gas, thickening Pluto's tenuous atmosphere. At night, it freezes back onto the surface. This daily cycle drives winds across the dwarf planet, making Sputnik Planitia the literal beating heart of Pluto's atmospheric circulation and weather patterns.