In the search for life across our Solar System, planetary scientists are concentrating much of their efforts on the liquid oceans we find beneath the frozen crusts of icy moons.
It seems unbelievable that a dwarf planet like Pluto, so far from the Sun, could host a liquid ocean beneath its surface.
But if it did, wouldn’t that make it one of the best places to search for signs of habitability beyond Earth?
Evidence for an ocean on Pluto
Water worlds beyond Earth are nothing new, with Jupiter’s moon Europa and Saturn’s moon Enceladus known to possess global oceans beneath their icy crusts, and perhaps the right kind of conditions for microbial life to evolve.
Both worlds’ oceans may be potentially habitable since evidence has been found for requisite nutrients and heat.
Water ice has been detected at Pluto, but could it have liquid water beneath its frozen surface?
In December 2016, it was reported that beneath its icy crust, Pluto’s internal heat could support a subsurface ocean at least 100km (60 miles) deep.
In June 2020, it was theorised that this putative ocean might even have been habitable when it first formed.
It could remain habitable today if conditions are warm enough and a source of geothermal heat exists at the ocean’s base.
Additionally, a life-enabling ocean would need to lack harmful toxins like hydrogen peroxide.
What a Pluto ocean would mean
If an ocean does exist beneath Pluto’s ice, it would reside much deeper and would be located in a darker, colder region of the Solar System, 4.5 times further into space than Europa and more than twice as distant as Enceladus: a potential showstopper for microbial life.
But it would demonstrate that liquid water oceans are possible, even at Pluto’s extreme distance from the Sun.
For now, however, the jury on Pluto’s ocean remains out.
This article appeared in the July 2025 issue of BBC Sky at Night Magazine