'X' Marks Strange Feature on Pluto's Icy Plains

An "X" marks an unusual spot on Pluto's plains. NASA's New Horizons spacecraft has beamed back an image of Pluto that reveals some intriguing surface activity on the dwarf planet.

In this case, the researchers are looking at the very center of Sputnik Planum, the informally named icy plain that forms the left side of Pluto's "heart" feature. This area is at a lower elevation than most of the surrounding area by a couple of miles, but is not completely flat. Its surface is separated into cells or polygons that are 10 to 25 miles wide. When viewed at low sun angles, the cells are seen to have slightly raised centers and ridged margins, with about 100 yards of overall height variation.

Mission scientists believe that the pattern of the cells within this plain stems from the slow thermal convection of the nitrogen-dominated ices that fill Sputnik Planum. A reservoir that's likely several miles or kilometers deep in some places, the solid nitrogen is warmed at depth by Pluto's modest internal heat, becomes buoyant and rises up in great blobs and then cools off and sinks again to renew the cycle.

"This part of Pluto is acting like a lava lamp," said William McKinnon, one of the researchers, in a news release. "If you can imagine a lava lamp as wide as, and even deeper than, the Hudson Bay."

Computer models by the New Horizons team show that these blobs of overturning solid nitrogen can slowly evolve and merge over millions of years. The ridged margins, like the "X" feature, mark where cooled nitrogen ice sinks back down.

The findings reveal a bit more about the dwarf planet and show just how these models manage to evolve and merge over millions of years.

For more information about the New Horizons mission, visit NASA's website.

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