The secret to all of that activity is Pluto’s probable underground ocean. The water ice on the surface of the world suggests that there should be more water hidden below ground. Over the course ...

(Correction: An earlier version of this story misstated how far Pluto is from the sun. The correct number is 3.7 billion miles.) What was discovered in Flagstaff, Arizona, and killed off in Prague?

But instead of surface water being evaporated by the Sun and falling as rain, Pluto experiences a daily nitrogen cycle. Nitrogen is heated and cooled as Pluto rotates. A New Horizons image of ...