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Pluto Demoted Day on August 24 commemorates the 2006 decision by the International Astronomical Union to reclassify Pluto as a dwarf planet. This day invites us to delve into planetary science and appreciate the vastness of our solar system. Join the conversation, learn about celestial bodies, and gaze at the night sky.
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History of Pluto Demoted Day
Pluto was discovered in 1930 by astronomer Clyde Tombaugh, making it the ninth planet in our solar system. It’s a relatively cold planet that exists outside the orbit of Neptune.
After its discovery, Lowell Observatory had over 1,000 suggestions for what to name the newly found planet. The eventual winner was Pluto, named after the Roman god of the underworld.
In 1992, questions arose around Pluto’s legitimacy as a planet after the discovery of large objects in its region, including one that actually had a larger mass than Pluto itself. Eventually, in 2006, the International Astronomical Union (IAU) settled on a definition for ‘planet,’ which ultimately excluded Pluto. From that point forward, it has been known as a ‘dwarf planet.’
A dwarf planet is defined as is a celestial body that orbits the sun and has enough mass to assume a nearly round shape but that has not cleared the area around its orbit and is not a moon.
Pluto Demoted Day timeline
Pluto is first discovered by Clyde Tombaugh and is determined to be the ninth planet in the solar system.
Charon — the largest of Pluto’s five moons, is discovered by the United States Naval Observatory.
In 2005, Eris, another dwarf planet larger in mass than Pluto, is discovered in the Kuiper belt (a region of icy objects outside Neptune’s orbit, which includes Pluto).
The International Astronomical Union (IAU) officially downgrades Pluto from a full-size planet.
Pluto Demoted Day FAQs
When is Pluto Demoted Day?
Pluto Demoted Day 2026 falls on Monday, August 24, marking the anniversary of the International Astronomical Union’s controversial 2006 decision.
What is a dwarf planet?
A dwarf planet, as defined by the IAU, is a celestial body that orbits the Sun, is nearly round, but has not cleared the neighborhood around its orbit. Pluto, Eris, Ceres, Makemake, and Haumea are the five officially recognized dwarf planets.
How many dwarf planets are in our solar system?
As of 2026, there are five officially recognized dwarf planets in our solar system: Pluto, Eris, Ceres, Makemake, and Haumea. However, astronomers estimate there could be hundreds or even thousands more awaiting official classification.
Why was Pluto demoted?
Pluto was demoted from a full planet to a dwarf planet in 2006 because it failed to meet one of the three criteria set by the IAU: it had not ‘cleared the neighborhood around its orbit.’ This means its gravitational pull wasn’t strong enough to remove other objects from its orbital path.
How to celebrate Pluto Demoted Day
Try some papier mâché!
We all remember making volcanoes out of papier mâché as kids and trying not to make too much of a mess. What better way to celebrate Pluto than to bust out some flour, water, and old strips of newspaper and make the solar system! It’s a great way to entertain kids while at the same time providing some planetary education.
Watch a space documentary
Documentaries about murders or celebrities tend to get a lot of press, but there are countless interesting ones about planets and the solar system. There is quite literally an entire universe outside your window to discover. Take this day as an excuse to plop down on the couch and learn more about Pluto and all the planets.
Try stargazing
Most of us can’t afford a powerful telescope like the ones at fancy observatories, but that doesn’t mean we can’t try out stargazing. It’s even possible to see Pluto! You’ll need a decent telescope and a detailed star atlas to help guide your search.
5 Facts About Pluto That Will Blow Your Mind
A day on Pluto is equivalent to six Earth days
Due to its distance from the Sun, a day on Pluto lasts 153 hours.
Where the name came from
A youngster by the name of Venetia Burney (only 11 years old) came up with the name Pluto in 1930.
Bring a winter jacket
The surface of Pluto is super cold, with a temperature ranging from -378°F to -396°F.
A long way from the Sun
Pluto sits 3.6 billion miles away from the Sun.
Planet X
Prior to its official discovery in 1930, astronomers suspected that there was another planet, which would help explain Uranus’s orbit, known as Planet X.
Why we love Pluto Demoted Day
Everyone likes an underdog
As the smallest planet in the solar system, it’s easy to cheer for Pluto. For generations people were taught that there were nine planets, including Pluto, orbiting the sun. Its reclassification as a dwarf planet sparked renewed interest in Pluto and the other planets in our arm of the Milky Way galaxy.
Fascination with the universe
There is still much to learn about the solar system and the larger universe in which we live. Pluto’s demotion is a reminder that we are still always learning and investigating, not only our planet Earth but also its sister planets. As astronomers and scientists uncover new information, reclassifications like this may be necessary.
Planets are fun
Planets are a topic that interests everyone, young or old. Whether you are a child first being exposed to the solar system, or an adult with a passing interest in astrology. Much like dinosaurs, there is something inherently tantalizing about the prospect of planets and their study. Having a day to focus on the now dwarf planet Pluto is a fun excuse to geek out.
