Caption: 
A team co-led by Southwest Research Institute found evidence for hydrothermal or metamorphic activity deep within the icy dwarf planets Eris and Makemake (artistic illustration). Located in the Kuiper Belt, a vast donut-shaped region of icy bodies beyond the orbit of Neptune at the edge of the solar system, Eris and Makemake are comparable in size to Pluto and its moon Charon.