What can cryovolcanism on Pluto teach scientists about the dwarf planet’s current geological activity? This is what a recent study published in *The Planetary Science Journal* hopes to address as a team of researchers investigated potential cryovolcanic sites within specific regions on Pluto. This study has the potential to help scientists better understand the current geological activity, including how it can be active while orbiting so far from the Sun.
For the study, the researchers examined the Kildaze caldera on Pluto, which resides in the dwarf planet’s Hayabusa Terra region, for evidence of past cryovolcanic activity. To accomplish this, the team used a combination of images obtained from NASA’s New Horizons spacecraft that flew past Pluto in July 2015 and compared them to other sites of cryovolcanism on Pluto, along with analogs sites on Earth and Mars. The cryovolcanic sites on Pluto include Virgil Fossae and Viking Terra, while analog sites on Earth include the Yellowstone caldera, Valles Caldera, and Long Valley Caldera. For Mars, these sites include collapsed pit craters located at Noctis Labyrinthus, which is a canyon-filled region on the western part of Valles Marineris, which is the largest canyon in the solar system.
Along with the New Horizons images and planetary analogs, the researchers used a series of digital elevation models, elevation profiles, and 3D visualizations models to ascertain the origins of the water ice that is present within Kildaze. In the end, the researchers concluded that the water ice present on Kildaze is approximately a few million years old, or possible older, but still much younger than the age of Pluto itself.
The study concludes, “In consideration of the size, structure, composition, and youth of Kiladze and its surroundings, we suggest that this region is a cryovolcano with a caldera structure, having a history of one or more eruptions ejecting 103 [1,000] km3 [cubic kilometers] of cryolava, and possibly an unknown number of eruptions of a smaller scale.”
As its name implies, cryovolcanism involves icy “magma”, as opposed to hot lava or magma like traditional volcanism. Ever since the term “cryovolcano” was first used in 1987, cryovolcanism has been observed on a myriad of worlds throughout the solar system, including Ceres, Europa, Ganymede, Enceladus, Titan, several Uranian moon, Triton, and Mars. Potential sources of cryovolcanism include external processes like crater impacts, tidal heating from two planetary bodies tugging on each other, or internal heat from radioactive decay.
What makes this study intriguing is that Pluto orbits the farthest from the Sun than any of those other planetary bodies, meaning that the Sun’s influence likely is not responsible for its potential cryovolcanic activity. Scientists continue to debate whether the potential source of Pluto’s internal heating is from tidal heating through interactions with its largest moon Charon, or radiogenic heating, which is the radioactive decay of isotopes within a planet’s interior. For example, a 2022 study published in Icarus hypothesized that Pluto’s internal heat was caused by tidal heating with its interactions with Charon and its size enabled that heat to remain within its interior long after Charon’s internal heat cooled. Additionally, Pluto’s internal heat has been hypothesized to have originated from its formation billions of years ago.
While New Horizons made its historic flyby in July 2015, it remains the only spacecraft to visit Pluto. Since then, several missions have been proposed to re-visit Pluto, including an orbiter-lander combination powered by a fusion reactor that is hypothesized to reach Pluto in only four years. For context, it took nine years for New Horizons to reach Pluto. In the meantime, scientists continue to pour over the data sent back by New Horizons with the goal of unlocking the dwarf planet’s secrets regarding its geological activity.
What new insights into Pluto’s cryovolcanic activity will researchers make in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!