Researchers analyzing data from NASA’s New Horizons spacecraft have found that liquid nitrogen may be rising through cracks and temporarily wetting the surface of Sputnik Planitia on Pluto. Published in the Planetary Science Journal, the findings offer the first evidence of recent liquid activity on the distant dwarf planet.
New Horizons Data Points to Subsurface Liquid Nitrogen
Dark streaks and diffuse markings across the northern reaches of Pluto’s giant heart-shaped glacier may record something entirely unexpected beneath the frozen crust. A study led by the Southwest Research Institute points to liquid nitrogen moving upward and briefly flowing across the surface of Sputnik Planitia. Researchers using observations gathered during NASA’s New Horizons spacecraft’s 2015 encounter with Pluto report that these patterns represent the first evidence of recently flowing liquid on the dwarf planet.
The work was led by Alan Stern, associate vice president at the Southwest Research Institute and principal investigator for the New Horizons mission.
“Pluto never stops surprising us, and this new result certainly does that. In addition to suggesting that liquids have recently expressed themselves on Pluto’s surface, this result also suggests a new kind of time-variable feature on Pluto.”
Alan Stern, principal investigator of New Horizons and lead study author from the Southwest Research Institute in Boulder, Colorado
Comparing Pluto’s Glacier to Earth’s Icy Landscapes
Atmospheric and thermal conditions on Pluto make liquid nitrogen rain physically impossible. To explain the darkened patterns on northern Sputnik Planitia, researchers compared the spacecraft’s observations with NASA Landsat 9 images of icy environments on Earth, including the Greenland ice sheet.
On Earth, narrow dark features appear where liquid water reaches snow and ice. The corresponding structures identified on Pluto share a striking resemblance, supporting the idea that nitrogen is moving upward from beneath the thick glacier and temporarily wetting the frozen surface.
Sputnik Planitia is a vast glacier made largely of frozen nitrogen, spanning an area larger than Texas and Oklahoma combined. Images collected by New Horizons revealed city-sized convection cells across its northern reaches, separated by narrow dark lines and broader patches of darker material.
“The surface of Sputnik Planitia is quite young, probably less than one million years based on modeling of the surface overturn, and thus these features that we are looking at must have formed since then.”
Dr. Kelsi Singer, principal scientist at SwRI and a co-author of the study
Mechanisms of Basal Melting and Pressure
Computer simulations led by Orkan Umurhan, senior research scientist at the SETI Institute, indicate how nitrogen could rise. The models show that nitrogen ice deep beneath Sputnik Planitia—which is several kilometers thick—can melt at the base of the glacier due to pressure, producing liquid nitrogen that then pushes upward.
As detailed in scientific research published in the Planetary Science Journal, that liquid must form under pressure at the base of the ice sheet before percolating through glacial ice, warming up, and eventually refreezing upon reaching the surface.
A Long Journey to the Edge of the Solar System
The discoveries build upon a historic mission that fundamentally altered scientific understanding of the outer solar system. Launched in early 2006, New Horizons spent more than nine years crossing roughly five billion kilometers to reach Pluto, executing a close flyby on July 14, 2015. Operating far from the Sun where solar panels are ineffective, the probe runs on a plutonium-powered nuclear battery.
Before the encounter, astronomers largely expected Pluto to be a frozen, cratered relic, geologically dead for billions of years. Instead, the flyby revealed flowing nitrogen glaciers, mountains of water ice standing kilometers high, and polygon-like surface patterns indicating continuous resurfacing.
Geological Activity and What Lies Beneath
The revelation that Pluto’s heart may conceal active nitrogen flow reinforces the view that the dwarf planet is geologically active despite its distant orbit. This activity also draws comparisons to other icy worlds across the solar system, such as Triton or Europa.
Beyond surface features, data from the New Horizons encounter indicated the presence of a heavier mass beneath Sputnik Planitia, leading researchers to infer that a liquid water ocean may be sloshing beneath Pluto’s icy crust.
Whether future missions will return to study Pluto via a dedicated orbiter remains uncertain, leaving researchers to extract further insights from the vast telemetry transmitted home by New Horizons.
