Astronomy
The Geological Evolution of Pluto's Heart-Shaped Glacier
Quick fact
NASA's New Horizons spacecraft revealed that Pluto's famous 'heart' is actually a massive glacier of nitrogen ice, filling a deep impact basin. This glacier is actively churning, with slow convection cells overturning its surface every few hundred thousand years.
Why this is interesting
You probably know Pluto as a tiny, frozen planet—so how can it have a heart-shaped glacier that flows and churns like a living thing?
Read the full explanation
Understanding The Geological Evolution of Pluto's Heart-Shaped Glacier
Pluto's heart-shaped glacier, known as Sputnik Planitia, is a vast plain of nitrogen ice that sits inside a huge impact crater. It's not just a static sheet; it behaves like a glacier on Earth but with a twist. On Pluto, the 'ice' is nitrogen, which is a gas on Earth. Because it is so cold, nitrogen freezes into a solid that can flow very slowly. This glacier is roughly 1,000 kilometers wide, and its surface is covered with polygonal patterns. These patterns are created by convection: warmer, denser ice rises from below, while cooler, denser ice sinks. These convection cells slowly churn the surface, erasing craters and creating a surface that is only a few million years old, which is very young in geologic terms. The glacier also appears to flow into surrounding plains, pushing against the underlying terrain.
A deeper explanation
The evolution of Sputnik Planitia is driven by two primary mechanisms: the deep basin it fills and the nature of nitrogen ice. The basin likely formed from a massive impact early in Pluto's history. This impact would have created a depression, which then collected volatile ices like nitrogen, because they condense from the atmosphere and accumulate in low-lying areas. The vast thickness of nitrogen ice acts as an insulator, trapping some heat from Pluto's interior. This heat causes the lower layers of the ice to warm and become buoyant, triggering thermal convection. As the ice convects, it creates the polygonal patterns we see. Over millions of years, this churning refreshes the surface, erasing impact craters and explaining why the glacier looks so smooth and young. Moreover, the glacial flow of nitrogen ice might also be causing subtle shifts in the planet's rotational axis, making the basin a 'true polar wander' feature. This process on a small, distant world is a striking example of how internal heat can sustain geological activity far from the Sun, challenging the assumption that only large planets are geologically active.