The New Horizons probe may have finished its Pluto flyby all the way back in July 2015, but NASA continues to receive new images from the spacecraft's slow, drip-feed data connection. The latest pictures add to our highest resolution mosaic of Pluto's surface, showing new detail of the Sputnik Planum — the icy plain that makes up the western half of Pluto's "heart."
This region of Pluto's surface is separated into huge cells, some 10 to 25 miles wide (16 to 40 kilometers). These areas are separated by ridged edges that show up as furrows in the landscape when the Sun's rays hit them at a low angle. Scientists believe that this patterning is created by convection in the nitrogen-dominated ice. Great globules of solid nitrogen are thought to be warmed by Pluto's "modest internal heat" before rising up to the surface, cooling, and sinking back down again. "This part of Pluto is acting like a lava lamp," said William McKinnon, deputy lead of the New Horizons Geology, Geophysics and Imaging team in a press release. "If you can imagine a lava lamp as wide as, and even deeper than, the Hudson Bay."
"A lava lamp as wide as, and even deeper than, the Hudson Bay."
In the image at the top of the page, an X-shaped feature is thought to be a spot where four of these convection cells once met, before the nitrogen cooled and fell back below the surface. The dark shape in the channels between the cells is probably a dirty water "iceberg" floating in the denser, solid nitrogen, while the numerous pits in Pluto's surface are thought to be the result of sublimation — solid ice turning directly into gas.
NASA has also released a new composite image of Pluto's (informally named) Viking Terra area (above). The picture combines data from New Horizons' Long Range Reconnaissance Imager (LORRI), taken at a distance of around 31,000 miles (49,000 kilometers), and enhanced color data from the probe's Ralph/Multispectral Visible Imaging Camera (taken 20 minutes later, when the spacecraft was at a range of around 21,000 miles).
The dark red spots in the image are thought to be aggregations of tholin (soot or tar-like matter created by reactions involving methane and nitrogen), while the bright, light rims of the many craters in view are likely to be created by methane ice. Scientists are particularly interested in areas where the tholin buildup looks thick and smooth, and has apparently flowed into channels. This is unusual because tholin deposits of this size aren't thought to be mobile, suggesting that the material might be "riding along with ice flowing underneath, or being blown around by Pluto’s winds."
Images credited to: NASA / JHUAPL / SwRI