Pluto’s Sputnik Planitia may be insulating its underground ocean. (Credit: NASA/JHU-APL/SwRI)

Pluto has left astronomers puzzled ever since the world was discovered in 1930. And its mysteries only grew in the aftermath of NASA’s New Horizons probe, which cruised by the dwarf planet in 2015. One point of confusion is Sputnik Planitia, part of the now-familiar heart-shaped region on Pluto’s northern hemisphere.

New Horizons’ instruments hinted that there might be an underground ocean in th