The ice giant planets Uranus and Neptune are water-rich worlds with deep layers of ice or possibly liquid water beneath their thick atmospheres. Their interior “oceans” are more extensive than the oceans on Earth or the ice deposits and/or subsurface lakes on Mars. There’s a lot we don’t know about the water layers on Uranus and Neptune. In May 2021, researchers in the U.S. and South Korea announced new findings suggesting the water layers of these exotic water worlds might be rich in magnesium. This finding provides clues to their interior chemistry.