Remember when Pluto went from being a planet to a dwarf planet in 2006? It's still the poster child for dwarf planets, but it's far from alone! In fact, our solar system could be teeming with potentially hundreds of these celestial bodies that remain undiscovered.

What is a Dwarf Planet?

So, what exactly classifies a celestial body as a dwarf planet? Simply put, a dwarf planet is smaller than a full-fledged planet but larger than your everyday asteroid or cosmic rubble. To be officially labeled a planet, an object must fulfill three criteria: it must orbit the sun, be mostly round, and have enough gravitational force to clear its orbital path of other objects. Dwarf planets meet the first two criteria, but fall short on the third, especially since they tend to linger in the Kuiper Belt—a distant area beyond Neptune filled with icy debris.

The Kuiper Belt: A Hidden Treasure Trove

When Pluto was identified back in 1930, it and similar Kuiper Belt objects were elusive, even for the best telescopes available at that time. The characteristics that define dwarf planets—small size and great distance—also pose significant challenges for astronomers trying to spot them.

Astronomers like Mathew Yu from UCLA explain, "They are far from the sun, making their reflected light faint. Some even have low reflectivity, further dimming their visibility. Plus, with their slow movement—taking hundreds of Earth years to orbit the sun—they become incredibly difficult to track against the backdrop of stars."

A Boom in Discoveries

Thanks to improved telescopes, astronomers made significant strides in detecting Kuiper Belt objects during the 1990s and 2000s. The clearer view led to the discovery of several large rocks, including Haumea, Makemake, Quaoar, Sedna, Orcus, Eris, and Salacia between 2002 and 2005.

The Birth of a New Category

The International Astronomical Union (IAU) recognized the need for a new category in 2006 to classify these sizable but unclaiming orbital bodies, sparking the term 'dwarf planet' into existence.

How Many Dwarf Planets Are There?

While many might assume there are only eight dwarf planets—thanks to the eight named items in the Kuiper Belt—experts are divided on this number. "Accepted estimates range from around 10 to a few hundred in the Kuiper Belt alone," Yu says. Some believe tens of thousands could exist beyond it!

The IAU has only officially recognized five dwarf planets: Pluto, Haumea, Makemake, and Eris in the Kuiper Belt, plus Ceres, which resides in the asteroid belt. Of these, we've dispatched probes to Pluto and Ceres, with NASA's New Horizons and Dawn spacecraft visiting in 2015.

The Expanding Roster of Dwarf Planets

However, the counting doesn't stop at five. Many astronomers include four additional bodies: Quaoar, Sedna, Orcus, and Gonggong—discovered in 2007 and confirmed through NASA observations in 2016. The IAU is still sifting through proposals related to these intriguing entities.

As of June 2025, a new candidate has emerged: 2017 OF201, a particularly faint object unearthed through advanced algorithms analyzing a trove of old data.

A World of Possibilities Awaits

When tallying all currently proposed dwarf planet candidates along with the newcomer, we could be looking at eighteen or more dwarf planets in our solar system right now! And that’s just scratching the surface; many more are likely hiding in the depths of space, waiting to be discovered as our telescopic technology continues to advance.