Dwarf Planets

Did you know that Pluto was once considered a planet but now is a dwarf planet? What exactly is a dwarf planet?

According to the International Astronomical Union or IAU, a dwarf planet must orbit a star like the Sun, have enough mass to be nearly spherical in shape, not have cleared smaller objects from the area around its orbit, and not be a moon.

There are five recognized dwarf planets: Pluto, Eris, Makemake, Haumea, and Ceres. The first four lie in the Kuiper Belt, while Ceres is in the asteroid belt.

When we compare their sizes, Pluto is the largest, followed by Eris, with a slightly smaller diameter than Pluto.

Makemake, the third-largest dwarf planet, is about 75% the size of Pluto. Haumea, which is oval-shaped, has its largest axis about the same diameter as Pluto's and its shortest axis about half as long.

The smallest one, Ceres, is only about 40% of Pluto’s size.

Like the planets, dwarf planets also have moons. Pluto has five, Haumea has two, Eris and Makemake each have one, and Ceres has none.