The exciting revelation comes just hours before NASA reveals details about Jupiter’s moon Europa – with many believing the announcement will also be about the discovery of subsurface water.
Experts have suspected Pluto has had a subsurface ocean since the New Horizon spacecraft flew past it last year.
Now experts at Brown University have been analysing the images sent by NASA’s spaceship, and concluded there is likely more than 100 kilometres of liquid water under Pluto’s surface.
Brandon Johnson, an assistant professor in Brown University’s Department of Earth, Environmental and Planetary Sciences, said: "Thermal models of Pluto's interior and tectonic evidence found on the surface suggest that an ocean may exist, but it's not easy to infer its size or anything else about it.
"We've been able to put some constraints on its thickness and get some clues about composition.”
The team, led by Mr Johnson, mainly focussed their research on the Sputnik Planum – a 900 kilometre stretch that makes up the western lobe of Pluto’s famous ‘heart’.
It is believed the Planum was caused by a giant meteor crashing into the dwarf planet.
Pluto is not much bigger than Earth's moon
However, as the team states, an impact would usually mean the area which had been hit would have a negative mass – essentially void of any content.
Mr Johnson said: "An impact crater is basically a hole in the ground. You're taking a bunch of material and blasting it out, so you expect it to have negative mass anomaly, but that's not what we see with Sputnik Planum.”
But what the researchers has found is that the crater has a positive mass, which they believe is a result of the asteroid hitting Pluto, which caused the subsurface ocean to even out across the dwarf planet.
Mr Johnson: "We wanted to run computer models of the impact to see if this is something that would actually happen.
“What we found is that the production of a positive mass anomaly is actually quite sensitive to how thick the ocean layer is.
"It's also sensitive to how salty the ocean is, because the salt content affects the density of the water.
"What this tells us is that if Sputnik Planum is indeed a positive mass anomaly – and it appears as though it is – this ocean layer of at least 100 kilometres has to be there.
"It's pretty amazing to me that you have this body so far out in the solar system that still may have liquid water."