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| (134340) Pluto | |
|---|---|
| Name | (134340) Pluto |
| Caption | True color mosaic from New Horizons (spacecraft) |
| Discoverer | Clyde Tombaugh |
| Discovery date | January 23, 1930 |
| Named after | Pluto |
| Mp category | Dwarf planet |
| Epoch | 2026 |
| Semimajor | 39.48 AU |
| Eccentricity | 0.2488 |
| Period | 247.94 yr |
| Inclination | 17.16° |
| Mean radius | 1188.3 km |
| Mass | 1.303×10^22 kg |
| Density | 1.88 g/cm³ |
| Satellites | 5 known |
(134340) Pluto is a trans-Neptunian dwarf planet located in the Kuiper belt beyond Neptune. Discovered in 1930, it has played a central role in debates over planetary definition involving institutions such as the International Astronomical Union and missions such as New Horizons (spacecraft). Pluto's complex system includes multiple moons, a heterogeneous surface, and a tenuous atmosphere observed by ground-based observatories like Arecibo Observatory and space telescopes like the Hubble Space Telescope.
Pluto was discovered by Clyde Tombaugh at the Lowell Observatory in 1930 using photographic comparisons that followed predictions from searches linked to Percival Lowell and the hypothetical Planet X concept. Early orbit determinations involved astronomers at Mount Wilson Observatory and calculations by Harold C. Urey and Kenneth Edgeworth; later, long-term astrometry used facilities such as the Palomar Observatory and the Very Large Telescope. Occultation observations coordinated by teams from European Space Agency member institutions and amateur astronomers improved size estimates prior to resolved imaging by Hubble Space Telescope, and definitive reconnaissance was provided by the New Horizons (spacecraft) flyby led by researchers at the Southwest Research Institute and Johns Hopkins University Applied Physics Laboratory.
The name Pluto was proposed by Venetia Burney and endorsed by representatives of Lowell Observatory and adopted by the International Astronomical Union; it honors the Roman god Pluto and preserves the astronomical symbol historically used by astronomers such as Percival Lowell. Pluto's classification shifted from planet to dwarf planet after the 2006 IAU General Assembly redefinition, a decision involving delegates and committees including representatives from institutions like Smithsonian Institution and provoking public debate covered by outlets like the New York Times and BBC News.
Pluto follows an eccentric, inclined orbit in 3:2 resonance with Neptune similar to many Plutino populations identified by surveys with the Sloan Digital Sky Survey and analyzed by researchers at Institute for Astronomy (University of Hawaii). Its orbital period of ~248 years places perihelion inside Neptune's orbit for part of its cycle; orbital elements were refined by teams using data from Gaia (spacecraft) and long-baseline observations at Mauna Kea Observatories. Pluto's rotation is ~6.387 days and is tidally coupled with its largest moon, an interaction studied by dynamics groups at Caltech and Massachusetts Institute of Technology.
Pluto's mean radius, mass, and density were constrained by stellar occultations, mutual events with moons, and New Horizons data analyzed by scientists at Southwest Research Institute, NASA, and European Southern Observatory. Its bulk composition includes volatile ices such as nitrogen, methane, and carbon monoxide, along with a rocky interior inferred by models developed at University of Arizona and Brown University. Thermal models and interior structure hypotheses involve researchers from Jet Propulsion Laboratory and comparative studies with Eris (dwarf planet) and Haumea populations.
High-resolution mapping by New Horizons (spacecraft) revealed diverse terrains including the ice plain informally named Sputnik Planitia, rugged mountains, and tectonic features; imaging teams involved scientists from Johns Hopkins University Applied Physics Laboratory, University of Colorado Boulder, and University of Leicester. Surface geology shows evidence for glacial flow, cryovolcanism hypotheses explored by groups at University of California, Santa Cruz and Brown University, and impact cratering records compared with bodies like Triton (moon) and Charon (moon). Spectroscopic mapping by instruments akin to those used at Keck Observatory and Gemini Observatory identified compositional heterogeneity across regions studied by planetary geologists from University of Arizona.
Pluto possesses a tenuous atmosphere chiefly of nitrogen with methane and carbon monoxide detected via spectrometers on Hubble Space Telescope and ground observatories such as IRTF; studies were conducted by teams at Cornell University and Massachusetts Institute of Technology. Seasonal changes driven by orbital eccentricity and axial tilt produce sublimation and condensation cycles observed during stellar occultations coordinated by organizations including the International Occultation Timing Association and analyzed by atmospheric modelers from University College London and University of Michigan.
Pluto's satellite system includes five known moons discovered through observations with Hubble Space Telescope and ground-based facilities: Charon, Styx, Nix, Kerberos, and Hydra; discovery teams included astronomers from Lowell Observatory, SETI Institute, and Southwest Research Institute. The binary-like mass ratio and barycentric motion with Charon inspired dynamical studies at Caltech and Princeton University; searches for rings and additional small satellites used data from New Horizons (spacecraft) and deep imaging from Gemini Observatory and Subaru Telescope.
Pluto was the primary target of the NASA New Frontiers mission New Horizons (spacecraft), launched by Kennedy Space Center and led by principal investigator Alan Stern from Southwest Research Institute. The spacecraft conducted a flyby in July 2015, with mission operations managed by teams at Johns Hopkins University Applied Physics Laboratory and data analysis by instrument teams from institutions such as NASA Goddard Space Flight Center, University of Colorado Boulder, and European Space Agency collaborators. Future mission concepts and observational campaigns have been proposed by researchers at NASA, ESA, JAXA, and academic centers including University of California, Los Angeles and University of Maryland.