A World Full of Surprises
When NASA's New Horizons spacecraft flew past Pluto in 2015, it completely changed our understanding of the dwarf planet. Instead of a dead, crater-pocked world, the probe revealed towering mountains of water ice, vast plains of frozen nitrogen, and stunning
evidence of recent geological activity. Before this historic flyby, scientists widely expected Pluto to be inert, having long ago lost the internal heat needed to power geological processes. Its small size and vast distance from the Sun seemed to guarantee a static existence. What New Horizons found has sent planetary scientists back to the drawing board, proving that small, icy worlds can have complex and active histories.
The Beating Heart of a Planet
One of the most iconic features revealed was a massive, heart-shaped basin named Tombaugh Regio. The western lobe of this feature, Sputnik Planitia, is a colossal glacier of frozen nitrogen, methane, and carbon monoxide stretching over 1,000 kilometers wide. What makes this area so remarkable is the complete lack of impact craters, which suggests the surface is incredibly young in geological terms—less than 10 million years old. The surface is broken into large polygonal cells, which are believed to be the result of slow, convective churning, like a giant lava lamp. This constant renewal process erases any craters that form, keeping the surface smooth and fresh. Recent studies even suggest liquid nitrogen may be flowing up from beneath the glacier, temporarily wetting the surface.
Volcanoes of Ice
Perhaps the most startling discovery was evidence of cryovolcanism—volcanoes that erupt icy slush instead of molten rock. Southwest of Sputnik Planitia lies a region dominated by enormous domes, including one feature named Wright Mons. This massive mound is about 150 kilometers across and 4 kilometers high, making it a candidate for the largest ice volcano ever discovered in the outer solar system. The very limited number of craters on Wright Mons and similar structures suggests they were active relatively recently in Pluto's history. Instead of lava, these volcanoes would have spewed a slurry of water ice, nitrogen, and ammonia from Pluto's interior, building up these massive structures over multiple eruption episodes.
An Engine of Buried Heat
So what is powering all this activity on a world where surface temperatures hover around minus 235 degrees Celsius? Scientists believe the answer lies deep beneath the ice. One leading theory is that Pluto retains some residual heat from its formation billions of years ago, which is insulated by its thick ice shell. Many scientists also theorize the existence of a vast subsurface ocean of liquid water, potentially mixed with ammonia which acts as an antifreeze. The slow freezing of this ocean could generate enough heat and pressure to crack the surface and power cryovolcanic eruptions. The sheer weight of the nitrogen ice in Sputnik Planitia could also be enough to melt nitrogen at the glacier's base, contributing to its flow and surface renewal.
