Dwarf planets like Pluto

So far, the International Astronomical Union, the astronomy world’s official record keeper, recognizes just five dwarf planets : Ceres, Eris, Haumea, Makemake, and Pluto. But astronomers keep finding new dwarf planet candidates every year.What is a dwarf planet? According to the IAU, a dwarf planet is a world orbiting the Sun that’s big enough for its gravity to make round, but may “orbit in a zone that has many other objects in it.” For example, while planets like Earth are occasionally hit by space rocks, they’ve largely swept the debris out of their orbits. In contrast, a dwarf planet like Ceres orbits in the asteroid belt.

But the weirdest of these worlds sit far from the Sun in the Kuiper Belt and share basic properties with Pluto. At the moment, these so-called Plutoids are mostly known from grainy images and via Earth-based detections of chemicals found on their surfaces.



That could soon change thanks to the next generation of large telescopes under construction in places like Chile and Hawaii. These instruments should reveal surface details better than even the Hubble Space Telescope can provide.



“The wide variety of geologic expression on Pluto really points to the type of things other than ice mountains that we will be on the lookout for on other dwarf planets,” says Southwest Research Institute planetary scientist Alan Stern, who leads the New Horizons spacecraft team. “I think we’re going to find that the dwarf planets of the Kuiper Belt are every bit as heterogeneous as the terrestrial planets.”



Stern and fellow SwRI astronomer Carly Howett are also planning a potential new NASA mission that would return and orbit Pluto before journeying on to visit other large Kuiper Belt objects.



Here’s a rundown of some of the most potentially exciting and unexplored dwarf planets.