Icebergs on Pluto: Mystery Of ‘Floating Hills’ Solved

Brand new data emerging from NASA’s New Horizons mission has revealed icebergs on Pluto, possibly solving the mystery of the “floating hills” that had puzzled astronomers since the images were transmitted last July.

The images exciting NASA and the international planetary scientific community were taken on July 14, 2015, during a flyby at New Horizons’ closest proximity to Pluto — a distance of about 9,950 miles. The New Horizons spacecraft has continued to transmit back images of the former planet taken on that date at resolutions high enough to reveal features smaller than half a city block or about 250 to 280 feet per pixel. The high resolution — five times sharper than any previously obtained of Pluto or its moons — has allowed scientists to refine their observations and posit possible conclusions.

Icebergs on Pluto are just the latest example of the geological activity exhibited by the dwarf planet that continues to fascinate planetary scientists. The images depict a region of the dwarf planet known as Sputnik Planum, a frozen plain that had previously been thought to be flat. However, New Horizons images showed a series of hills that seemed to clump along areas of Sputnik Planum, in addition to a mountain range on the western side. Other observations included oddly shaped segments of the plain that were separated by troughs, with dark material appearing at the juncture of some segments.

Scientists marveled at Pluto’s frozen topography but could offer no firm explanations at the time. Today, astronomers have announced a possible explanation – icebergs on Pluto. Like icebergs on earth, the icebergs on Pluto are floating, but it’s a case of ice floating on ice. The hills represent chunks of water ice that is floating on a sea of nitrogen ice. Nitrogen ice, being denser than water ice, creates the buoyancy that holds up the icebergs on Pluto.


Planetary scientists theorize that the action is similar to the way icebergs float on earth’s Arctic Ocean., although the physics involved in outer space operates differently than it does here on earth. Scientists believe that the nitrogen sea moves in a cycle very slowly over millions of years, creating the complicated structures observed today. The water icebergs drift over the frozen nitrogen ocean. Astronomers believe the icebergs on Pluto observed on Sputnik Planum are smaller versions of the much larger mountains observed on the plain’s western borders. A NASA New Horizons news update explains.

“The hills are likely fragments of the rugged uplands that have broken away and are being carried by the nitrogen glaciers into Sputnik Planum.”

According to NASA’s data, the iceberg hills each measure up to several miles across. The icebergs on Pluto move over time, in essence floating along the plain of frozen nitrogen until they clump together. The clumping patterns of the icebergs follow the flow of the underlying nitrogen glaciers in what they believe is a cycling motion that sees the icebergs on Pluto slowly driven back out towards the shoreline via convection motion. A 40-mile wide cluster of icebergs on Pluto has been dubbed “Challenger Colles” in honor of the crew of the Space Shuttle Challenger that tragically exploded not long after lift-off three decades ago. Astronomers believe that Challenger Colles was formed as the icebergs essentially beach on a shallow section of the nitrogen ice.


Icebergs on Pluto are just the latest discovery to emerge from a study of the high-resolution images, which include vast mountain ranges and a mysteriously textured surface. The entire downlink of data from the flyby is expected to take approximately one year, with scientists anticipating more revelations to emerge from the data as time goes by.

[Image via NASA/JHUAPL/SwRI]