Finding Pluto: How the planet got its heart of ice

Pluto has an ever-changing climate, covered in nitrogen ice, methane frost and even a giant glacier. Photo / NASA

Pluto has a peculiar and ever-changing climate - covered in nitrogen ice, methane frost and even a giant glacier.

Now a new model has used computer simulations to change our understanding of how the glacier at the heart of the dwarf planet formed.

The massive glacier is mostly made of nitrogen ice mixed with carbon monoxide and methane - covers the 4 km deep, 1000 km wide basin of Sputnik Planum, found within the heart-shaped region on Pluto's surface.

In July 2015, Nasa's New Horizons spacecraft made a flyby of the dwarf planet, and took close-up images of its surface.

Now researchers at the University Pierre and Marie Curie (UPMC) in Paris have studied the images and developed a computer model to study how Pluto evolved.

"In order to better understand the cycle of nitrogen, methane and carbon monoxide ices on Pluto, we developed a thermal model of the surface able to simulate the condensation and sublimation processes and the transport of these ices over thousands of years," Tanguy Bertrand, lead author of the study told MailOnline.

The model showed the glacier at the heart of Pluto was not formed by an internal reservoir of nitrogen, as previous studies have suggested.

The paper, published in Nature, reports on a model lasting 50,000 Earth years.
Each 50,000-year cycle of the simulation took just three days to run.

When researchers added topography to the computer model, they found that basins and craters gradually trap nitrogen, carbon monoxide, and methane.

This is because Pluto's atmosphere is thickest at lowest elevation.

As a result, condensation of the ices is greatest in these regions.

"We show that the glacier is trapped in the basin, probably since the basin has been created," Mr Bertrand said.

"Flowing and extending at lower scale over the seasons, the glacier eroded and shaped the mountains surrounding it."

The results of the model were backed up by observations from New Horizons, which showed Pluto has a varied landscape.

"It is fascinating to see how a tiny icy object like Pluto, far from the sun, can offer such a diversity of colours, landscape and activity," Mr Bertrand said.

The researchers will use future observations to test and improve their models.

The model also predicts that most of the seasonal frosts should disappear in the next decade.

"We predict with the model that atmospheric pressure is at its seasonal peak and will decrease in the next decades, and that the seasonal frosts of methane will tend to disappear," Mr Bertrand said.

"Observing Pluto in the next years will validate or challenge our model."