Welcome to this audio long read from nature.

In this episode, Pluto's dark side spills its secrets, including hints of a hidden ocean.

Written by Shannon Hall and read by me, Benjamin Thompson.

When NASA's New Horizons spacecraft zipped past Pluto in 2015,

it showed a world that was much more dynamic than anyone had imagined.

The dwarf planet hosts icy nitrogen cliffs that resemble the rugged coast of Norway

and giant shards of methane ice that

saw to the height of skyscrapers. Cracks deeper than the Grand Canyon scar the surface, while icy

volcanoes rise taller than Mount Everest. In one part of the distant orb, the spacecraft's cameras

captured a giant heart-shaped feature

that caused a collective swoon among countless fans on Earth.

I expected Pluto to be a scientific wonderland, but it did not have to be so beautiful,

says Leslie Young, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, and a

deputy project scientist on the New Horizons mission.

Although scientists caught that first jaw-dropping glimpse nearly five years ago, they are still

seeing images of the world for the first time.

When New Horizons reached the dwarf planet, the craft was moving at 52,000 kilometres per hour.

So fast, it was able to capture close-ups of only one side of Pluto, the hemisphere that the sun illuminated

at the time. The other was temporarily shrouded in shadow. Now that scientists have scrutinized

those near-side close-ups, they are beginning

to analyse the other half, which the spacecraft photographed days before it shot past.

Researchers call that hemisphere the far side, or even the dark side. Although the images

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