On July 14, 2015, NASA’s New Horizons spacecraft carried out the first flyby of Pluto, one of the most enigmatic worlds in the Solar System. Although that meeting was brief, the impressive images and enormous … The volume of data obtained revealed a surprisingly dynamic, vibrant planet full of surprises. There we have, as an example, the already famous ‘heart of Pluto’, the floating ice hills or icebergs and the nitrogen winds. But the New Horizons data went much further, also hinting at the existence of an ocean of liquid water beneath the planet’s icy crust. Something totally unexpected so far from the Sun and that led Pluto (and also its largest moon, Charon) to enter the select club of “ocean worlds.”
Today, almost a decade later, numerous teams of researchers continue to make important discoveries thanks to the information from New Horizons. And now, in a new paper just published in ‘Icarus’, planetary scientists Alex Nguyen and Patrick McGovern, from the University of Washington and the Lunar and Planetary Institute in Houston, have revealed interesting new data about the planet’s possible ocean, placing it between Pluto’s icy surface and its metallic core.
In their analysis, in fact, the researchers determined that Pluto’s ocean lies beneath an icy mantle that is between 40 and 80 km thick, an insulating layer that is thick enough to ensure that the interior ocean does not freeze. and remain in a liquid state.
An extreme and cold world
For decades, planetary scientists assumed that Pluto was too cold to have an interior ocean. The planet’s orbit, in fact, lies far beyond the so-called ‘Ice Line’ of the Solar System, the limit after which volatile elements (water, carbon dioxide, ammonia, etc.) become solid. With an average surface temperature of -229 degrees Celsius, even nitrogen and methane are, on Pluto, as solid as a rock. As Nguyen points out, “Pluto is a small body. “It should have lost almost all of its heat shortly after forming, so basic calculations suggest it is frozen to its core.”
But New Horizons changed that idea forever, and for 10 years scientists have been accumulating more and more evidence indicating that, most likely, Pluto still keeps heat inside, which allows the existence of an interior ocean, just as which happens in several moons of Jupiter and Saturn such as Europa, Ganymede, Enceladus or Titan, in the asteroid Ceres or, also, in the largest Plutonian moon, Triton.
The ocean scores points
While the existence of this ocean is still subject to some debate, ocean supporters are still gaining points. To gain even greater certainty, Nguyen and McGovern created mathematical models that could explain the cracks and bulges seen in the ice covering Pluto’s Sputnik Planitia basin, where several meteorites fell billions of years ago.
The results indicate that it is perfectly possible for an ocean to exist under an icy layer 40 to 80 km thick, which would be enough to isolate it from external inclemencies and keep it in a liquid state despite the surface conditions. The researchers also calculated the likely density and salinity of that ocean based on surface characteristics, and determined that it could be up to 8% denser than Earth’s oceans. This level of salinity would make Pluto’s ocean comparable to the Dead Sea and other high-salinity bodies of water on Earth.
According to Nguyen, any variation in this density (higher or lower) would be evident from the cracks and fractures of the Sputnik Planitia basin itself. “We estimate,” says the scientist, “that there is a kind of ‘Goldilocks’ zone where the density and thickness of the layer are correct.” If the ocean were less dense, the ice sheet would collapse, causing many more fractures on the surface. If, on the other hand, it were denser, the ice layer would be more compact and solid, which would lead to fewer fractures.
Unfortunately, it could be several decades before another spacecraft reaches Pluto to help confirm these findings. In the meantime, we will have to continue making the most of the information collected by New Horizons. And continue accumulating evidence that confirms that Pluto’s ocean is a reality.
