At https://www.nature.com/articles/d41586-023-03271-4 … we are told Mars has a surprise layer of molten rock in its interior. This conclusion came about after a meteor struck the surface of Mars in 2021. Scientists analyses the seismic energy that vibrated through the planet and discovered a layer of molten rock probably exists – enveloping its core.
At https://www.livescience.com/space/pluto/pluto-may-have-an-ice-spewing-supervolcano-the-size-of-yellowstone-new-horizons-data-reveals/ … Pluto, once considered a planet but now classified as a big space rock, may sport a big volcano, it would seem. Images captured by NASAs New Horizons mission suggest a cryovolcano – or ice spewing. There are problems with this idea as Pluto is on the outskirts of the solar system and is assumed to be very cold. On the other side of the argument – could the solar wind induce a volcano that far away?