Science & Technology

Two decades after Pluto’s demotion: The redefinition that redrew the solar system

A visual tour of Pluto’s icy vistas and the scientific upheaval that turned a distant world into a new class of planet
Pluto's bladed terrain as seen from NASA's New Horizons during its July 2015 flyby.
Pluto's bladed terrain as seen from NASA's New Horizons during its July 2015 flyby.NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
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In August 2006, the International Astronomical Union voted to redefine what constitutes a full-fledged planet, famously reclassifying Pluto as a "dwarf planet." The decision followed the discovery of similar distant worlds beyond Neptune, spark of a historic debate. Here is a visual journey through Pluto’s incredible landscapes and the cosmic discovery that changed its status forever.

Captured on July 13, 2015, by NASA's New Horizons spacecraft from a distance of approximately 768,000 kilometres during its historic flyby approach. It showed a high-resolution global view highlighting Pluto’s brilliant, light-colored, heart-shaped region, informally named Tombaugh Regio in honor of Pluto's discoverer Clyde Tombaugh. The western lobe of the "heart" is rich in nitrogen, carbon monoxide, and methane ices, revealing unexpected surface diversity and geologic activity.
Captured on July 13, 2015, by NASA's New Horizons spacecraft from a distance of approximately 768,000 kilometres during its historic flyby approach. It showed a high-resolution global view highlighting Pluto’s brilliant, light-colored, heart-shaped region, informally named Tombaugh Regio in honor of Pluto's discoverer Clyde Tombaugh. The western lobe of the "heart" is rich in nitrogen, carbon monoxide, and methane ices, revealing unexpected surface diversity and geologic activity. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Portrait of Pluto and its binary companion Charon, composed from two images taken by NASA’s New Horizons spacecraft in July 2015. Charon is the largest of Pluto’s five moons and, at half Pluto’s size, is the largest known satellite relative to its parent body. Pluto and Charon are mutually tidally locked, meaning the same hemispheres of both bodies always face each other. Charon orbits Pluto every 6.4 Earth days.
Portrait of Pluto and its binary companion Charon, composed from two images taken by NASA’s New Horizons spacecraft in July 2015. Charon is the largest of Pluto’s five moons and, at half Pluto’s size, is the largest known satellite relative to its parent body. Pluto and Charon are mutually tidally locked, meaning the same hemispheres of both bodies always face each other. Charon orbits Pluto every 6.4 Earth days.NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
A twilight glow across pluto’s atmosphere. Pluto’s dark silhouette is surrounded by a glowing ring of complex, layered atmospheric hazes extending more than 80 miles into space. The backlit view revealed Pluto’s haze-rich nitrogen atmosphere and distinct thermal layers, providing key data on atmospheric pressure and the interaction of methane and nitrogen under solar ultraviolet light.
A twilight glow across pluto’s atmosphere. Pluto’s dark silhouette is surrounded by a glowing ring of complex, layered atmospheric hazes extending more than 80 miles into space. The backlit view revealed Pluto’s haze-rich nitrogen atmosphere and distinct thermal layers, providing key data on atmospheric pressure and the interaction of methane and nitrogen under solar ultraviolet light. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
This image was taken on October 21, 2003, and later used in the discovery of Eris, formerly known as 2003 UB313 or Xena, announced on January 5, 2005. Named after the Greek goddess of discord and strife, Eris helped trigger a debate that led the International Astronomical Union (IAU) to clarify the definition of a planet in 2006. Pluto, Eris and other similar objects are now classified as dwarf planets.
This image was taken on October 21, 2003, and later used in the discovery of Eris, formerly known as 2003 UB313 or Xena, announced on January 5, 2005. Named after the Greek goddess of discord and strife, Eris helped trigger a debate that led the International Astronomical Union (IAU) to clarify the definition of a planet in 2006. Pluto, Eris and other similar objects are now classified as dwarf planets.NASA/JPL/Caltech
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