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Meet Wright Mons: Pluto’s Massive Ice Volcano

Our first color view of what could be the largest ice volcano in the outer Solar System.
Imae: NASA

The New Horizons spacecraft is well on its way to its next target in the Kuiper Belt, but continues to supply us with new views of Pluto. The latest image release gives us our first color view of what could be the largest ice volcano in the outer Solar System.

Unofficially named Wright Mons in honor of the Wright brothers, the massive ice caldera is located just south of Pluto's icy heart: a frozen terrain named Sputnik Planum. Wright Mons is quite massive, spanning 90 miles across and 2.5 miles high. Resembling the shield volcanoes we see on Earth, Wright Mons would spew an icy slurry of ammonia and nitrogen as opposed to rock and lava. The closest analogue to Wright Mons can be found on Mars. Olympus Mons is the largest volcano in the inner Solar System and spans a whopping 374 miles across and 16 miles high.

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Wright Mons is located just south of Sputnik Planum: Pluto's famous icy heart-shaped region. The smooth, frozen terrain of Sputnik Planum is one of the most surprising features as scientists were expecting to see a heavily-cratered surface. Instead we see a dynamic, young surface with evidence that atmospheric and surface processes are shaping the landscape.

Pluto is 3.67 billion miles from the Sun, yet even in the frigid regions of the Kuiper Belt, ice still flows on the surface as seen in Sputnik Planum. The western half of Pluto's icy heart is divided into cell-like structures spanning up to 25 miles wide. Scientists believe that thermal convection within Pluto's nitrogen ice is creating this unique surface pattern.

The New Horizons team believes that Sputnik Planum is the result of a giant impact. A newly published paper estimates that the planum's surface is 10 million years old and implies that it's refreshed by cryo-geological processes. Heat radiating from within Pluto's interior—most likely the radioactive decay of elements left over from its formation over 4.5 billion years ago—is fueling thermal convection. Globs of nitrogen are heated by the convection, causing them to rise to the surface. As the melted nitrogen ice is exposed to sub zero surface temperatures, it refreezes and settles. Sort of like a giant nitrogen lava lamp. In some regions of Sputnik Planum, visible surface pits are thought to be caused by sublimation (meaning the nitrogen ice went directly from a solid to a gas). Since Pluto's surface is covered in volatile ices, it doesn't take as much heat to melt as it would for molten rock.

Sputnik Planum is bordered by several mountain ranges which scientists predict could also be a result of the giant impact thought to create the planum. Alan Stern, New Horizons principal investigator recently spoke at the 227th meeting of the American Astronomical Society, saying "Many of the mountain ranges that border Sputnik Planum appear to be a jumbled mass rather than individual peaks. This could be a direct result of the giant impact predicted to create the planum."

Especially intriguing to scientists is the red material seen in the recent images of Wright Mons. Scientists are curious as to why the material is not widespread across Pluto's surface. The red material is thought to be tholins—which are soot or tar-like organic materials formed when nitrogen and other volatiles are blasted with UV radiation. Also intriguing is the lack of craters around Wright Mons.

Craters are good age indicators and the lack of impact craters on a planetary surface indicates to scientists that some sort of geologic process is taking place to fill in the crater. Looking at Wright Mons, scientists noticed there was only one crater present…at the mountain's summit. This tells us that if Wright Mons is an ice volcano, it was active in recent geologic history.

Could Wright Mons have been born as a result of this giant impact, and could convection processes have fueled the volcano? Once scientists gather all the data from New Horizons, they will be able to better piece together the clues.