Previously, UW360 reported on the speculation of there being life on Jupiter’s moon Europa. Now there is growing evidence to suggest that Pluto may host an ocean.
Ever since New Horizons transferred images of Pluto from the dwarf planet’s orbit back to Earth in 2015, Pluto has grown in the imaginations of scientists and science enthusiasts around the world – and now it’s making waves in the space industry with speculation that it contains a deep ocean.
Whilst an earlier study showed that Pluto’s core was warm enough to support a liquid water ocean, a new study has gone one step further to suggest that this liquid water ocean may be at least 100 kilometres deep (almost 10 times deeper than our own). To understand the study further, UW360 speaks to Brandon Johnson, Brown University geologist and lead author of the study.
Pluto has captured science enthusiasts’ imagination. There are not many planetary scientists who expected to see such a geologically active and dynamic world when we got our first look at Pluto,” states Johnson. “The first images from New Horizons were spectacular and completely changed how we think about [the dwarf planet].”

An animation combining various observations of Pluto over the course of several decades. © NASA Public Domain

Finding an ocean

The team developed models of Pluto to estimate how thick this buried ocean could be. The models looked into impact dynamics to help estimate how much liquid may be lying beneath the surface. Cited in the study was both surface-level “tectonic evidence” as well as interior thermal models as factors in the estimates – both indicated that a liquid water ocean with high salt levels could potentially be buried within.

Exploration of Pluto Timeline

1930: Pluto Discovered by a young astronomer named Clyde W. Tombaugh in the Lowell Observatory

1978: Images released of Pluto’s moon Charon

1988: NASA confirms that Pluto has a thin nitrogen atmosphere (an atmosphere that appears to have expanded rapidly in subsequent decades)

2005: The Hubble Space Telescope distinguishes Pluto from Charon and in doing so discovers that Pluto has more that one moon – raising the number of Plutonian moons to three

2006: Discovery of new “small” planets leads scientists to define Pluto as a dwarf planet, removing it from the list of classical planets

2010: Hubble captures the best “fuzzy” images so far of Pluto

2011: Astronomers discover a fourth Pluto moon

2012: A fifth moon is discovered orbiting Pluto

2015: New Horizons photographs the “new-look” Pluto, and sparks excitement in space explorers to continue studying the dwarf planet

The hints about Pluto’s underground ocean revolve around the planet’s “heart”, which has been named Sputnik Planum. “Sputnik Planum is aligned with Pluto’s tidal axis. This tells us the crater has a positive mass anomaly. Craters are essentially holes in the ground so if there wasn’t a dense ocean to uplift, the crater would have a negative mass anomaly.”
Based solely on observation, the region is a giant impact crater and sits at the tidal axis that links the planet with its biggest moon, Charon. It’s the way that the planet and its moon are locked together that has sparked interest from researchers, who have estimated that the Sputnik Planum region has a higher level of mass than elsewhere on the planet.
But how sure can one be based on observation and estimates? “There is a growing body of evidence suggesting that Pluto has a global subsurface ocean,” Johnson says. “Detailed thermal models as well as the tectonics on Pluto also point toward a liquid ocean. It is always possible that further investigation could overturn some findings but I expect the story of Pluto‘s ocean is here to stay.”
Water on Pluto means a great deal to space exploration. “[Water on Pluto] tells us that oceans may be quite ubiquitous on icy bodies. There are a number of other dwarf planets and they may have oceans too.” Johnson also expresses an interest in exploring other dwarf planets such as Eris, or other large objects in the Kuiper Belt, to see if Pluto and its potential ocean might be completely unique.
Due to the impact basin, Sputnik Planum being formed by a large object slamming into the ground and ejecting material away, the researchers would expect a negative – rather than positive – mass anomaly. Part of the reason is nitrogen ice building up in the impact basin, but researchers aren’t convinced that there is enough ice present in great enough quantities to be the sole explanation. Because of this, there is speculation that liquid has to exist beneath the surface, a welling of water beneath the impact zone which returned the area to neutral mass.
This composite of enhanced color images of Pluto (lower right) and Charon (upper left), was taken by NASA’s New Horizons spacecraft as it passed through the Pluto system on July 14, 2015. © NASA Public Domain

This composite of enhanced colour images of Pluto (lower right) and Charon (upper left), was taken by NASA’s New Horizons spacecraft as it passed through the Pluto system on July 14, 2015. © NASA Public Domain

Does water equal life?

“Astrobiologists may be thinking about [life on Pluto] but Pluto‘s ocean is a harsh environment. The ocean is probably colder than 240°K (–33°C) and kept liquid by abundant ammonia and salt. The prospects for life in Europa’s ocean are much better,” says Johnson.
Realistically, in temperatures so cold and conditions so extreme, the type of life is – if at all – likely to be simple extremophile life, similar to those basic life forms on Earth that have adapted to withstand hydrothermal vents and extreme temperatures.
High-resolution images of Pluto taken by NASA’s New Horizons spacecraft just before closest approach on July 14, 2015, are the sharpest images to date of Pluto’s varied terrain—revealing details down to scales of 270 metres. © NASA Public Domain

High-resolution images of Pluto taken by NASA’s New Horizons spacecraft just before closest approach on July 14, 2015, are the sharpest images to date of Pluto’s varied terrain – revealing details down to scales of 270 metres. © NASA Public Domain

But with no more planned missions, speculation is going to have to remain speculation for a while longer before anybody decides to revisit again.
“It took New Horizons almost a decade to make it out to Pluto,” Johnson points out, “so even if a space agency decided to send another spacecraft to Pluto or another large Kuiper Belt object, it would be at least a decade before we started getting back data. I am hopeful that New Horizons will spur greater interest in the outer Solar System, and we can send another spacecraft to the outer reaches of the Solar System soon.”