Evidence for Large-Scale Cryovolcanism on Pluto

Oblique view of Wright Mons exhibiting its central depression and surrounding hummocky terrain on its flanks. The surface and atmospheric haze are in grayscale, and blue areas highlight an artistic interpretation of possible past cryovolcanism. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Isaac Herrera/Kelsi Singer.

The New Horizons mission revolutionized our understanding of Pluto with its 2015 fly-by, revealing a diverse planetary surface with a range of apparent ages. The topographic rises of Wright and Piccard Montes dominate a region southwest of Sputnik Planitia that displays a relative paucity of craters, indicating a young surface age. This apparent youth and the broad resemblance of the montes to volcanic edifices suggest cryovolcanic resurfacing in the region. Cryovolcanism is a collection of processes whereby subsurface water-ice in cold environments can extrude onto the surface as lava does on Earth.

A team of New Horizons scientists led by Kelsi Singer of the Southwest Research Institute analyzed the geomorphology of this region using imagery from the Long Range Reconnaissance Imager (LORRI), finding many large domes from 1 to 7 kilometers high and 30 to >100 kilometers wide, which often overlap and merge to form complex structures. The flanks of these large rises exhibit interconnected mounds and depressions termed hummocky terrain, which is suggestive of viscous flow, but no indicators of flow vent location or directionality were apparent at the resolution of the data. The team also analyzed infrared spectra from the Linear Etalon Imaging Spectral Array (LEISA), finding that the domes in this region are predominantly water-ice and that the methane-ice present is likely a thin surface layer deposited out of the atmosphere.

A cryovolcanic origin of Wright and Piccard Montes and the surrounding terrain requires multiple episodes of eruption from several sites that collectively extruded >10,000 cubic kilometers of material, a type and scale of cryovolcanism not seen elsewhere in the solar system. The emplacement of these massive structures requires subsurface mobilization of water-ice-rich materials, which in turn requires heat. Their relative youth necessitates that the heat was available late in Pluto’s history, which provides new insights into the thermal history of the dwarf planet. READ MORE