‘Make Pluto a planet again.’ See NASA chief back the dwarf planet
NASA head Jared Isaacman says Pluto should be a planet again during a Senate budget testimony before Congress.
For 76 years, generations of students learned that our solar system had nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Now, in 2026, some still can’t get over Pluto’s demotion to a dwarf planet.
Pluto, discovered in 1930, was the small, icy world at the end of the planetary list, often remembered through classroom mnemonics like “My Very Educated Mother Just Served Us Nine Pizzas.” Things changed on Aug. 24, 2006, when the International Astronomical Union (IAU) voted to redefine what qualifies as a planet and reclassified Pluto as a dwarf planet. The decision sparked widespread public debate, with students, teachers and even some astronomers objecting to the change, Smithsonian Magazine notes.
Today, Pluto remains a dwarf planet under the IAU’s definition; however, the debate has never fully gone away. As astronomers continue discovering unusual worlds beyond our solar system, many say the question that divided scientists in 2006 remains difficult to answer: What exactly is a planet?
Why was Pluto reclassified?
The issue came to a head after astronomers discovered Eris in 2005, an icy world beyond Pluto that is even more massive. According to National Geographic, the discovery forced scientists to decide whether to keep expanding the list of planets or finally establish a formal definition of the word “planet,” which previously had no official scientific meaning.
At its General Assembly in Prague in 2006, the IAU voted that a planet must orbit the Sun, be nearly round because of its own gravity and have cleared most other objects from the area around its orbit.
Pluto met the first two requirements but not the third because it shares its orbital neighborhood with many icy objects in the Kuiper Belt beyond Neptune, according to National Geographic. As a result, it was reclassified as a dwarf planet.
From Planet X to Pluto
American astronomer Clyde Tombaugh discovered Pluto at Arizona’s Lowell Observatory after months of comparing photographs of the night sky with a blink comparator, a device that revealed moving objects. His discovery confirmed the long-suspected existence of a ninth planet beyond Neptune.
Named after the Roman god of the underworld, Pluto remained the solar system’s ninth planet until the 2006 IAU vote.
Why do scientists still disagree?
While the IAU’s definition of a planet remains the official one, not every scientist agrees with it.
NASA New Horizons principal investigator Alan Stern has argued for years that dwarf planets should still be considered planets. Other astronomers have questioned whether the current definition goes far enough, particularly as researchers discover rogue planets, brown dwarfs and other unusual objects that blur the boundaries between planets, moons and stars. According to National Geographic, those discoveries have made the debate over planetary definitions even more complicated than it was 20 years ago.
Pluto continues to surprise scientists
NASA’s New Horizons spacecraft launched in January 2006, months before Pluto’s reclassification, and became the first mission to fly past the distant world in 2015.
According to NASA, the spacecraft revealed Pluto to be far more complex than scientists expected, uncovering towering mountains, nitrogen ice glaciers, vast plains and signs that parts of its surface are geologically active. The mission transformed Pluto from a tiny point of light into one of the solar system’s most intriguing worlds.
Contributing: USA TODAY reporter Elizabeth Weise
Reporter Anthony Thompson can be reached at ajthompson@usatodayco.com or on X @athompsonUSAT.