 Pluto is the largest dwarf planet and the closest to the Sun. The second largest is Eris. It's actually a little heavier than Pluto, which means it's also a little denser. We'll have more about Eris tomorrow. Most of these distant little worlds have icy surfaces, but a few could have active interiors with possible oceans of liquid water. That means at least some of them are possible habitats for life. In the deep freeze of the outer solar system,