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Pluto’s bladed terrain is product of its complex geological history

Bladed terrain on Pluto

Pluto’s bladed terrain as seen from New Horizons during its July 2015 flyby. Image & Caption Credit: NASA / JHUAPL / SwRI

A new study of Pluto’s bizarre “bladed terrain”, which stretches as high as skyscrapers on Earth, has identified them as being composed largely of methane ice, formed through erosion caused by long-term changes in the dwarf planet’s climate.

Discovered by NASA’s New Horizons spacecraft during its July 2015 Pluto flyby, the bladed terrain, which resembles huge “knife blades” pointing up, has mystified scientists, who could not explain the formation’s origin.

For the group of researchers led by New Horizons team member Jeffrey Moore of NASA’s Ames Research Center in California, the first clue about the terrain’s origin is that it is located at the highest altitudes on Pluto’s surface in regions near the equator.

At these high altitudes, methane can freeze out of the atmosphere and fall to the ground as snow. Like Earth, Pluto has a hydrologic cycle of evaporation and condensation, but one that uses methane instead of water.

That hydrologic cycle has driven the formation of its bladed terrains and giant ridges.

“When we realized that bladed terrain consists of tall deposits of methane ice, we asked ourselves why it forms all of these ridges, as opposed to just being big blobs of ice on the ground,” Moore said. “It turns out that Pluto undergoes climate variation[,] and[,] sometimes, when Pluto is a little warmer, the methane ice begins to basically ‘evaporate’ away.”

Pluto topography and composition graphic

The maps above are from New Horizons’ data on the topography (top) and composition (bottom) of Pluto’s surface. In the high-resolution topographical map, the highlighted red region is high in elevation. The map below, showing the composition, indicates the same section also contains methane, color-coded in orange. One can see the orange features spread into the fuzzier, lower-resolution data that covers the rest of the globe, meaning those areas, too, are high in methane, and therefore likely to be high in elevation. Image & Caption Credit: NASA / JHUAPL / SwRI / LPI

During warmer periods, the methane ice on the bladed terrain sublimates into atmospheric gas. The level of sublimation that occurs varies depending on the amount and concentration of sunlight reaching each region.

Similar structures, known as penitentes, also exist on Earth’s surface at high-altitude snowfields near the equator. Although they are only several meters high, they have the same spiky textures as their much larger counterparts on Pluto.

Penitentes Ice Formations in Chile

Penitentes ice formations at the southern end of the Chajnantor plain in Chile. Although these ice formations only reach a few meters in height, whereas Pluto’s bladed terrain can reach hundreds of meters in height, they both have similar sharp ridges. Photo Credit: Wikimedia Commons / ESO

Over millions of years, changes in Pluto’s climate and resulting variations in its surface and air temperatures caused ongoing geological activity. Methane that initially froze onto high-elevation areas subsequently turned to gas and evaporated into the atmosphere, causing a unique form of erosion that drove the formation of these unusual structures.

The New Horizons data used by the research team features high-resolution images of one side of Pluto but only low-resolution images of the other side due to the distance and speed of the spacecraft as it approached the dwarf planet.

While the high-resolution side shows only a small region of bladed terrain, the understanding that methane is present in high-altitude areas makes it possible for scientists to infer its presence at the upper altitudes of the side measured only in low resolution.

Various data collected on Pluto’s “far side” suggest the presence of similar bladed terrain there, enabling scientists to begin mapping out those areas.

These findings indicate both Pluto’s surface and atmosphere are more dynamic than previously believed and will provide new insights into the evolution of its climate and geology over time.

A paper on the study has been published in the journal Icarus.

Video courtesy of NASA’s Ames Research Center

 

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Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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