Pluto once had rivers and lakes of liquid nitrogen, New Horizons data suggests

Artist’s conception of Pluto’s surface, with the distant Sun and largest moon Charon in the sky. The surface is frozen now, but evidence suggests that rivers and lakes of liquid nitrogen once flowed here. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker
Artist’s conception of Pluto’s surface, with the distant Sun and largest moon Charon in the sky. The surface is frozen now, but evidence suggests that rivers and lakes of liquid nitrogen once flowed here. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker

As has been discussed extensively now, New Horizons has revealed Pluto to be a place unlike any other in the Solar System, with vast plains and glaciers of nitrogen ice, tall mountains of solid water ice capped with methane snow, layers of haze in its atmosphere, and perhaps an ocean of water below the surface. Now, there is additional evidence that Pluto once had rivers and lakes of liquid nitrogen on its surface, during times when the atmosphere was thicker than it is now. Just when you think Pluto can’t get any more bizarre, it does.

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Pluto revealed: Five new Science papers highlight discoveries by New Horizons

High-resolution view of Pluto from New Horizons. The large smoother area of ice in Sputnik Planum is the western lobe of the “heart” feature. Image Credit: NASA/JHUAPL/SwRI
High-resolution view of Pluto from New Horizons. The large smoother area of ice in Sputnik Planum is the western lobe of the “heart” feature. Image Credit: NASA/JHUAPL/SwRI

Pluto is a tiny world in the outer fringes of the Solar System; for many decades it was only a mere speck of light in even the best telescopes, with only vague hints of surface features. Then, in July 2015, the New Horizons spacecraft flew past Pluto, the first time ever that humanity would get to see this mysterious place up close – and it did not disappoint. An enormous amount of data has continued to be sent back by New Horizons since the flyby, and now five new papers have been published which provide an in-depth overview of the findings so far about Pluto and its moons. Pluto is an active world, with its own unique geology different from anywhere else in the Solar System.

Read MorePluto revealed: Five new Science papers highlight discoveries by New Horizons

New Horizons discovers methane ‘snow’ on Pluto’s mountain peaks

Methane “snow” on mountain peaks in the Cthulhu region of Pluto. The enhanced colour version of the inset image is on the left and the false colour version is on the right. The image covers an area 450 kilometres (280 miles) long by 225 kilometres (140 miles) wide. Image Credit: NASA/JHUAPL/SwRI
Methane “snow” on mountain peaks in the Cthulhu region of Pluto. The enhanced colour version of the inset image is on the left and the false colour version is on the right. The image covers an area 450 kilometres (280 miles) long by 225 kilometres (140 miles) wide. Image Credit: NASA/JHUAPL/SwRI

As the data from New Horizons continues to come in, we are learning more about what an incredible little world Pluto really is, with tall mountains of rock-hard water ice, as well as glaciers and vast icy plains composed of nitrogen ice. In some ways, these features are visually reminiscent of similar ones on Earth, and now this week another cool discovery was revealed: methane snow on some of Pluto’s mountain peaks.

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New Horizons finds evidence for frozen ocean inside Pluto’s moon Charon

The canyons of Charon, some of which dwarf the Grand Canyon on Earth. Image Credit: NASA/JHUAPL/SwRI
The canyons of Charon, some of which dwarf the Grand Canyon on Earth. Image Credit: NASA/JHUAPL/SwRI

One of the most surprising discoveries in recent years in the outer Solar System is that there are small moons which have oceans inside them. Jupiter’s moon Europa and Saturn’s moon Enceladus are now known to have global oceans of water beneath their icy crusts, and others are thought to as well, including Ganymede, Titan, and possibly others. These moons have a lot of ice and rock as well, and gravitational tugging and heating from the large gas giant planets helps maintain a deep layer of liquid water inside them, where otherwise they would most likely be frozen solid in the deep cold so far from the Sun. Now it seems that another moon also once had an ocean, although in this case it is thought to now be solid ice: Pluto’s largest moon, Charon.

Read MoreNew Horizons finds evidence for frozen ocean inside Pluto’s moon Charon

The ‘floating hills’ of Pluto: Icebergs in a frozen nitrogen sea

Icebergs on Pluto: The large blocks of water ice float in a “sea” of nitrogen ice and are thought to have broken off from the rugged and mountainous highlands. Image Credit: NASA/JHUAPL/SwRI
Icebergs on Pluto: The large blocks of water ice float in a “sea” of nitrogen ice and are thought to have broken off from the rugged and mountainous highlands. Image Credit: NASA/JHUAPL/SwRI

Pluto is a tiny world and incredibly distant from the Sun, so it was a pleasant surprise for scientists last summer when the New Horizons spacecraft found that it is such a geologically active and dynamic place, with vast “seas” of nitrogen ice and glaciers, tall mountains of rock-hard water ice, and possible ice volcanoes. A new update this week focuses on some of the most interesting features discovered: iceberg-like blocks of water ice which “float” in the “seas” of softer nitrogen ice.

Read MoreThe ‘floating hills’ of Pluto: Icebergs in a frozen nitrogen sea