Pluto is an interesting place. It lives in a frozen part of the solar system, and yet it has global dynamical processes that continue to shape and renew its surface. And now, in new observations beamed back to Earth from NASA's New Horizons mission over the Christmas Holidays, new detail in its surface activity has been revealed.
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This portion of a larger, high-resolution mosaic of Pluto's now-famous ice plain - informally known as Sputnik Planum (the smooth western half of the heart-shaped Tombaugh Reggio) - shows an intreguing "X" etched into the surface ices. (Is it the solar system's way of reminding us that the new "X-Files" airs this month? Maybe.)
Known to be composed mainly of nitrogen ices, planetary scientists believe that this mysterious formation is actually an artifact of large scale convection activity in the region. Sputnik Planum is made up of huge 10 to 25 mile wide polygonal cells with raised centers and edges. This fascinating and very alien landscape is only the tip of the proverbial iceberg, however.
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According to mission scientists, Sputnik Planum's "ocean" of nitrogen ices could be several miles deep and, through the gentle heating from Pluto's core, an extremely slow convection process is underway. Over millions of years, heated ice at the bottom of the reservoir becomes buoyant and rises to the surface. As it reaches the surface, it cools and then sinks once more, restarting the cycle. As a result, convection cells leave an imprint in the surface.
"This part of Pluto is acting like a lava lamp," said William McKinnon, deputy lead of the New Horizons Geology, Geophysics and Imaging team, from Washington University in St. Louis, "if you can imagine a lava lamp as wide as, and even deeper than, Hudson Bay."
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As for the mysterious "X", well that's the four corners of four convection cells that have long been convected away, leaving only this ghostly imprint behind for New Horizons to photograph with its Long Range Reconnaissance Imager (LORRI) during the historic flyby on July 14, 2015.