Pluto may not be a planet, but it has a hidden ocean

Astronomers have uncovered significant evidence of a massive ocean of liquid water beneath Pluto’s icy surface, unraveling some of the dwarf planet’s secrets. This breakthrough, detailed in the journal Icarus, sheds new light on the composition and characteristics of this distant celestial body.

### Uncovering Pluto’s Hidden Ocean

The research, led by Alex Nguyen, a graduate student in Earth, Environmental, and Planetary Sciences at Washington University in St. Louis, utilized mathematical models and images from NASA’s New Horizons spacecraft to probe Pluto’s subsurface ocean. The study, co-authored by Patrick McGovern from the Lunar and Planetary Institute in Houston, addresses long-standing questions about the presence of liquid water on Pluto.

### Pluto: More Than Just a Frozen Rock

Discovered by Clyde Tombaugh in 1930, Pluto was initially classified as the ninth planet in our solar system. However, in 2006, the International Astronomical Union (IAU) reclassified it as a dwarf planet. Pluto orbits the Sun at an average distance of 5.9 billion kilometers, completing one orbit approximately every 248 Earth years. It is smaller than Earth’s moon, with a diameter of about 2,372 kilometers.

### Composition and Moons

Pluto is primarily composed of rock and ice, featuring a diverse landscape that includes mountains, valleys, plains, and an ocean. Its thin atmosphere consists mainly of nitrogen, methane, and carbon monoxide. Pluto has five moons: Charon, Nix, Hydra, Kerberos, and Styx. Charon, the largest, is nearly half the size of Pluto itself.

### The Possibility of Liquid Water

Scientists previously believed that Pluto’s extremely cold surface temperature of -220°C, which freezes gases like nitrogen and methane, would preclude the existence of liquid water. Basic calculations suggested that Pluto, due to its smaller size, would have lost most of its heat shortly after formation, making it a solid frozen body.

However, recent observations of cryovolcanoes, which erupt with ice and water vapor, support the theory of a subsurface ocean. Esteemed scientists, including William B. McKinnon of WUSTL, now agree that Pluto likely harbors a vast ocean beneath its icy crust.

### Delving into Pluto’s Subsurface Ocean

Nguyen and McGovern’s research delves into the specifics of Pluto’s hidden ocean. They developed mathematical models to explain the cracks and bulges in the ice covering the Sputnik Planitia Basin. This enormous basin, formed by a meteor impact billions of years ago, provides clues about the ocean below. Their models indicate that the ocean is protected by a 40-to-80-kilometer-thick (25-to-50-mile-thick) shell of water ice. By examining surface fractures, they estimated the ocean’s density and salinity.

Nguyen describes a “Goldilocks zone” where the density and shell thickness are optimal. The findings suggest Pluto’s ocean is at most about 8% denser than Earth’s seawater, comparable to the Great Salt Lake in Utah. This density implies that humans would float effortlessly if they could reach Pluto’s ocean.

### Future Exploration

While there are no immediate plans to revisit Pluto, these findings pave the way for future exploration and research. The discovery of a liquid water ocean beneath Pluto’s icy surface challenges our understanding of this distant world and opens new avenues for planetary exploration, demanding a reevaluation of its internal composition and processes.