NASA’s New Horizons spacecraft sent back to Earth an intriguing surface image of Pluto. Long Range Reconnaissance Imager (LORRI) extends the highest-resolution views of Pluto to the very center of the icy plain that is informally named as Sputnik Planum, which forms the left side of the dwarf planet’s “heart” feature.
A lower elevation than most areas by several miles, Sputnik Planum isn’t completely flat at all. The icy plain’s surface is separated into polygons or cells 16 to 40 kilometers (10 to 25 miles) wide. The cells can be seen to have slightly raised centers and ridged margins, with approximately a hundred yards or a hundred meters of overall height variation.
The pattern of the cells, mission scientists believe, stems from the nitrogen-dominated ices’ slow thermal convection. Pluto’s modest internal heat warms the solid nitrogen, a reservoir that scientists believe several kilometers or miles deep in some places. The solid nitrogen then becomes buoyant and rises in great blobs. It eventually cools off and sinks again to repeat the cycle.
Washington University’s New Horizons Geology, Geophysics, and Imaging team leader, William Mckinnon, said that particular area of the dwarf planet is acting like a lava lamp, which is probably as wide as or even deeper than the Hudson Bay.
New Horizons team’s computer models reveal that the overturning solid nitrogen’s blobs can slowly evolve and merge over millions of years. The ridged margins mark where cooled nitrogen ice sinks back down. They can be pinched off and abandoned. Very likely, the ‘X’ feature is one of these – formerly quadruple junction where 4 convection cells meet. A couple of active triple junctions can be seen in other areas in the LORRI mosaic.