The newest high-resolution images of Pluto from NASA’s New Horizons are both dazzling and mystifying, revealing a multitude of previously unseen topographic and compositional details.
The image above, which shows an area on Pluto’s best-mapped hemisphere near the line that separates day from night, captures a vast rippling landscape of strange, aligned linear ridges that has astonished New Horizons team members.
“It’s a unique and perplexing landscape stretching over hundreds of miles,” says William McKinnon, a New Horizons Geology, Geophysics and Imaging (GGI) team deputy lead from Washington University in St. Louis. “It looks more like tree bark or dragon scales than geology. This’ll really take time to figure out – maybe it’s some combination of internal tectonic forces and ice sublimation driven by Pluto’s faint sunlight.”
The “snakeskin” image of Pluto’s surface is just one tantalizing piece of data New Horizons sent back in recent days. The spacecraft also captured the highest-resolution colour view yet of Pluto – along with detailed spectral maps and other high-resolution images.
The new ‘extended colour’ view of Pluto – taken by New Horizons’ wide-angle Ralph/Multispectral Visual Imaging Camera (MVIC) on 14 July and downlinked to Earth on 19 September – shows the extraordinarily rich colour palette of Pluto.
“We used MVIC’s infrared channel to extend our spectral view of Pluto,” said John Spencer, a GGI deputy lead from Southwest Research Institute (SwRI) in Boulder, Colorado. “Pluto’s surface colors were enhanced in this view to reveal subtle details in a rainbow of pale blues, yellows, oranges, and deep reds. Many landforms have their own distinct colours, telling a wonderfully complex geological and climatological story that we have only just begun to decode.”
Additionally, a high-resolution swath across Pluto taken by New Horizons’ narrow-angle Long Range Reconnaissance Imager (LORRI) on 14 July, and downlinked on 20 September, homes in on details of Pluto’s geology. These images, the highest-resolution yet available of the dwarf planet, reveal features that resemble dunes, the older shoreline of a shrinking glacial ice lake, and fractured, angular, jammed-together water ice mountains with sheer cliffs.
This closer look at the smooth, bright surface of the informally named Sputnik Planum shows that it is actually pockmarked by dense patterns of pits, low ridges and scalloped terrain. Dunes of bright volatile ice particles are a possible explanation, mission scientists say, but the ices of Sputnik may be especially susceptible to sublimation and formation of such corrugated ground.
Beyond the new images, new compositional information comes from a just-obtained map of methane ice across part of Pluto’s surface that reveals striking contrasts: Sputnik Planum has abundant methane while the region informally named Cthulhu Regio shows none, apart from a few isolated ridges and crater rims. Mountains along the west flank of Sputnik lack methane as well.
The distribution of methane across the surface is anything but simple, with higher concentrations on bright plains and crater rims, but usually none in the centers of craters or darker regions. Outside of Sputnik Planum, methane ice appears to favour brighter areas, but the team aren’t sure if that is because methane is more likely to condense there or that its condensation is what brightens those regions.
“It’s like the classic chicken-or-egg problem,” says Will Grundy, New Horizons surface composition team lead from Lowell Observatory in Flagstaff, Arizona. “We’re unsure why this is so, but the cool thing is that New Horizons has the ability to make exquisite compositional maps across the surface of Pluto, and that’ll be crucial to resolving how enigmatic Pluto works.”
“With these just-downlinked images and maps, we’ve turned a new page in the study of Pluto beginning to reveal the planet at high resolution in both colour and composition,” adds New Horizons Principal Investigator Alan Stern. “I wish Pluto’s discoverer Clyde Tombaugh had lived to see this day.”