At a recent Senate hearing on NASA’s 2027 budget request, NASA’s Administrator Jared Isaacman made a comment that reopens a question many in the scientific community had considered closed: should Pluto once again be classified as a planet?
Since its discovery in 1930, Pluto held the status of the solar system’s ninth planet. That changed in 2006, when the International Astronomical Union (IAU) introduced a formal definition of what constitutes a planet.
Under those rules, a celestial body must meet three criteria: it must orbit the Sun, be massive enough for its gravity to shape it into a sphere, and clear its orbital path of debris.
Pluto meets the first two conditions, but not the third. Located in the Kuiper Belt – a region populated with many similar icy bodies – it lacks the gravitational dominance required to clear its orbit. As a result, the IAU reclassified it as a ‘dwarf planet’.
The issue resurfaced at the end of the Senate hearing, when Republican Senator Jerry Moran of Kansas raised the topic. The question was a personal one for Moran: Pluto was discovered by Clyde Tombaugh, a Kansas native.
Isaacman replied, saying he was “very much in the camp” of restoring Pluto’s planetary status. He said that NASA is currently working on scientific papers that he would like to “escalate through the scientific community to revisit this discussion”.
Part of the renewed interest could stem from developments over the past decade. In July 2015, NASA’s New Horizons spacecraft delivered the first close-up images of Pluto, revealing a surprisingly complex world. The pictures showed mountains, nitrogen-ice glaciers, and a geologically diverse surface, features that challenged earlier assumptions about the dwarf planet.
Yet despite these discoveries, the IAU, which is the only internationally recognised authority for assigning designations to celestial bodies, has not revisited its 2006 decision.
For now, Pluto remains officially classified as a dwarf planet. Whether that status will change depends on the strength of the scientific arguments NASA may soon put forward.