Underground ocean found on Pluto, likely slushy with ice

An image of Pluto taken in July 2015, as Nasa's New Horizons spacecraft passed by, 768,000km above the surface.
An image of Pluto taken in July 2015, as Nasa's New Horizons spacecraft passed by, 768,000km above the surface.PHOTO: REUTERS

HOUSTON (REUTERS) - Scientists have found evidence that tiny, distant Pluto harbours a hidden ocean beneath the frozen surface of its heart-shaped central plain containing as much water as all of Earth's seas.

The finding, reported on Wednesday (Nov 16) in two research papers published in the journal Nature, adds Pluto to a growing list of worlds in the solar system beyond Earth believed to have underground oceans, some of which potentially could be habitats for life.

Pluto's ocean, which is likely slushy with ice, lies 150km to 200km beneath the dwarf planet's icy surface and is about 100km deep, planetary scientist Francis Nimmo of the University of California, Santa Cruz said in an interview.

With its ocean covered by so much ice, Pluto is not a prime candidate for life, added Massachusetts Institute of Technology planetary scientist Richard Binzel, another of the researchers. But Binzel added that "one is careful to never say the word impossible."

Liquid water is considered one of the essential ingredients for life.

The discovery was made through an analysis of images and data collected by Nasa's New Horizons spacecraft, which flew past Pluto and its entourage of moons in July 2015.

"It shows that nature is more creative than we are able to imagine, which is why we go and explore," Binzel said. "We see what nature is capable of doing."

Despite being about 40 times farther from the sun than Earth, Pluto has enough radioactive heat left over from its formation 4.6 billion years ago to keep water liquid.

"Pluto has enough rock that there's quite a lot of heat being generated, and an ice shell a few hundred kilometers thick is quite a good insulator," Nimmo said. "So a deep subsurface ocean is not too surprising, especially if the ocean contains ammonia, which acts like an antifreeze."

Scientists made the discovery as they were trying to figure out why a 1,000km-wide impact basin known as Sputnik Planitia, which contains the curious heart-shaped region, was located in its present position near Pluto's equator.

Computer models showed the basin likely filled with ice, which caused Pluto to roll over, cracking its crust. That could happen only if Pluto possessed a subsurface ocean, the analysis found.

New Horizons is on its way to another frozen world in the Kuiper Belt region of the solar system about 1.6 billion km past Pluto. A flyby of the object, known as 2014 MU69, is scheduled on Jan 1, 2019.