In the icy expanses of our Solar System, two domes tower over the surface of the dwarf planet Pluto. These two structures have long questioned researchers. Some have speculated that these could be cryovolcanoes spewing large amounts of melting ice. A comprehensive analysis of the images and topographic data returned by the probes confirms these suspicions.
The icy domes of Pluto
Located at the southern edge of a vast heart-shaped ice sheet, these two unusual surface features were initially spotted by the New Horizons probe, which passed through the region in July 2015. “We were immediately intrigued by this area, because she was so different and striking,” Dr Kelsi Singer, of the Southwest Research Institute in Boulder, Colorado, told the Guardian.
These two structures are two large mounds. The first rises four to five kilometers and is about 150 km wide. The second climbs to seven kilometers high and measures about 250 km in diameter. Both also display very deep depressions at their tops. Finally, many parts of the estate display a lumpy appearance, lined with wavy and rounded mounds.
The researchers quickly imagined that these smaller mounds, formed from small ice volcanoes, could have accumulated over time to form these two main mounds. At the time, this explanation of “ice volcanoes” seemed to be the least strange. This hypothesis was further supported by the absence of nearby impact craters, which suggests that these features had been erased by relatively recent geological events (ice flows). Finally, Pluto lacks plate tectonics which is a key contributor to mountain formation on Earth.
Yet researchers have always erred on the side of caution. While they could indeed be cryovolcanoes on paper, there are few such structures in the Solar System and none of these features resemble those of Pluto.
Two cryovolcanoes belching muddy ice
Since these first images shared in 2015, researchers have received and analyzed many others. Compositional and topographical data have also come down to us. Taking this whole picture together, Dr. Singer’s team confirms that these unusual features are truly ice volcanoes.
Regarding the nature of the material released, the composition data suggests that it is mainly water ice mixed with several antifreeze components such as ammonia or methanol. Don’t imagine perfectly liquid flares (the average surface temperature on Pluto is around -233 C°), but rather muddy material, perhaps even mostly solid.
Although researchers don’t yet fully understand this Plutonian cryovolcanic activity, it is likely fueled by radiogenic heat created by the decay of radioactive elements inside the dwarf planet. This may suggest Pluto’s rocky core is hotter than expected.