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Pluto and New Horizons Timeline
(1930 - Present)This timeline covers the discovery of Pluto by Clyde Tombaugh in 1930, its decades as the ninth planet, its controversial reclassification as a dwarf planet in 2006, and NASA's New Horizons mission, which performed the first close flyby of Pluto on July 14, 2015, revealing a surprisingly active and geologically diverse world. More Less
Discovery and Early Observations
Percival Lowell begins search for Planet X
Mar 15, 1905
Astronomer Percival Lowell began a systematic search for a hypothetical ninth planet, dubbed 'Planet X', whose gravity he believed was perturbing the orbits of Uranus and Neptune. He built the Lowell Observatory in Flagstaff, Arizona, for this purpose and spent years photographing the sky, though he died in 1916 without finding it.
Image source: Percival Lowell
Clyde Tombaugh discovers Pluto
Feb 18, 1930
Young astronomer Clyde Tombaugh, working at Lowell Observatory, discovered Pluto by comparing photographic plates taken in January 1930. The discovery of a new planet beyond Neptune made headlines worldwide, and Tombaugh became celebrated as the discoverer of the ninth planet.
Image source: Clyde Tombaugh
Pluto officially named after Roman god of the underworld
Mar 24, 1930
Following an international naming contest, the new planet was named Pluto at the suggestion of Venetia Burney, an 11-year-old English schoolgirl. The name honored the Roman god of the underworld and also echoed the initials of Percival Lowell.
Image source: Pluto
Pluto's moon Charon discovered
Jun 22, 1978
Astronomer James Christy at the U.S. Naval Observatory noticed a bulge on photographic images of Pluto, revealing its largest moon, Charon. The discovery allowed scientists to calculate Pluto's mass for the first time and revealed that Charon is remarkably large relative to Pluto, making them nearly a double system.
Image source: Charon (moon)
Occultation observations hint at Pluto's thin atmosphere
Aug 29, 1985
When Pluto passed in front of a star, observers detected that starlight dimmed gradually rather than abruptly, indicating Pluto possessed a tenuous atmosphere of nitrogen and other gases. This surprising finding reshaped scientific expectations about the distant dwarf planet.
Image source: Atmosphere of Pluto
Hubble maps Pluto's surface features
Jun 1, 1994
The Hubble Space Telescope captured the first images resolving surface features on Pluto, revealing bright and dark patches across its face. Though blurry compared to later spacecraft views, these maps provided the first hints of geological diversity on Pluto's surface.
Image source: Geology of Pluto
Hubble discovers Pluto's fourth moon, Kerberos
Jul 20, 2011
Astronomers using the Hubble Space Telescope discovered a small fourth moon orbiting Pluto, later named Kerberos. Its presence raised questions about how such a tiny body could remain in a stable orbit among Pluto's growing family of satellites.
Image source: Kerberos (moon)
Hubble discovers Pluto's fifth moon, Styx
Jul 7, 2012
Hubble observations revealed yet another tiny moon around Pluto, named Styx. With five known moons, Pluto's complex satellite system prompted mission planners to search carefully for debris hazards that could threaten New Horizons during its high-speed flyby.
Image source: Styx (moon)
New Horizons Mission
NASA cancels the Pluto Kuiper Express mission
Sep 13, 2000
NASA cancelled its planned Pluto Kuiper Express mission due to rising costs and shifting priorities, disappointing planetary scientists who warned that Pluto's atmosphere might freeze out as it moved away from the Sun. Public outcry over the cancellation helped spur a competition for a cheaper alternative mission.
Image source: Pluto Kuiper Express
NASA selects New Horizons as its Pluto mission
Nov 29, 2001
After a competitive proposal process, NASA selected New Horizons, led by principal investigator Alan Stern of the Southwest Research Institute, as the first mission to Pluto under its New Frontiers program. The spacecraft would carry seven scientific instruments to study Pluto and its moons.
Key Facts
- Pluto was discovered on February 18, 1930, by astronomer Clyde Tombaugh at Lowell Observatory in Arizona.
- In 2006, the International Astronomical Union (IAU) reclassified Pluto from a planet to a 'dwarf planet' after defining new criteria for what constitutes a planet.
- NASA's New Horizons spacecraft launched on January 19, 2006, and became the first mission to visit Pluto, flying by on July 14, 2015.
- New Horizons revealed that Pluto has a heart-shaped nitrogen ice glacier (Sputnik Planitia), mountains made of water ice, and possible subsurface ocean.
- Pluto has five known moons: Charon, Styx, Nix, Kerberos, and Hydra, with Charon being so large that Pluto and Charon are sometimes considered a double system.
Source
This Pluto and New Horizons timeline was generated with the help of AI, using information found on the internet.
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