Pluto

Dwarf Planet· orbits the Sun

Pluto is a dwarf planet in the Kuiper belt — a world of nitrogen ice plains, water-ice mountains and a thin atmosphere, explored up close by New Horizons in 2015.

Open in 3D viewSee Pluto in the live, interactive 3D map

Key facts

Mass

1.30 × 10²² kg

0.177 Moon masses

Radius

1,188 km

19% of Earth's radius

Surface gravity

0.616 m/s²

6% of Earth's

Day length

6.4 days

Year

251 Earth years

91,576 Earth days

Distance from Sun

39.8 AU

Moons

Charon, Styx, Nix, Kerberos & Hydra

Science

Physical

Mass: 1.30 × 10²² kg · 0.177 Moon masses
Radius: 1,188 km · 19% of Earth's radius
Density: 1,854 kg/m³ · 1.9× water
Surface gravity: 0.616 m/s² · 6% of Earth's
Escape velocity: 1.21 km/s · 11% of Earth's
Axial tilt: 122.53 °

Orbital

Distance from the Sun: 35.6 AU
Semi-major axis: 39.8 AU
Eccentricity: 0.2511
Inclination: 23.46 °
Orbital period: 250.72 years
Perihelion: 29.8 AU
Aphelion: 49.7 AU
Mean orbital velocity: 4.72 km/s

Rotation

Rotation period: 6.4 days

Atmosphere

Composition: N₂ with CH₄ and CO
Surface pressure: 1 Pa

Temperature

Minimum: 33 K (-240 °C)
Mean: 44 K (-229 °C)
Maximum: 55 K (-218 °C)

Composition

Bulk composition: Rock and water-ice interior; nitrogen-ice surface

Radiation & temperature

Insolation: 0.000633 S⊕ · 1/1,581 of the sunlight Earth receives
Bond albedo: 0.72 · reflects 72% of incoming sunlight
Equilibrium temperature: 32 K (-241 °C)
Measured mean temperature: 44 K (-229 °C)
Greenhouse warming: +12 K

Discovery & history

Discovered: February 18, 1930
By: Clyde Tombaugh
Method: Photographic plates
Name: The Roman god of the underworld — suggested by 11-year-old Venetia Burney. Its initials, PL, also honour Percival Lowell.

Pluto was found by 24-year-old Clyde Tombaugh at the Lowell Observatory, who painstakingly compared photographic plates with a blink comparator until, on 18 February 1930, a faint dot shifted between exposures. Hailed as the ninth planet, Pluto turned out to be tiny — and the first of many icy worlds in the Kuiper belt. The 2005 discovery of the more massive Eris led the IAU to reclassify Pluto as a 'dwarf planet' in 2006. New Horizons revealed its true face in 2015.

2015New HorizonsFlyby
First and only spacecraft to visit Pluto, revealing nitrogen-ice plains and water-ice mountains.

Images

Pluto in true colour, imaged by New Horizons — NASA / Johns Hopkins APL / SwRI (public domain) · Wikimedia Commons

New Horizons Sees Pluto — NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute · NASA Image Library

New Horizons Very Best View of Pluto Mosiac — NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute · NASA Image Library

New Horizons Very Best View of Pluto — NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute · NASA Image Library

New Horizons Best Close-Up of Pluto Surface — NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute · NASA Image Library

Pluto Icy Plains Captured in Highest-Resolution Views from New Horizons — NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute · NASA Image Library

First Pluto-Charon Color Image from New Horizons — NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute · NASA Image Library

Blue Rays: New Horizons High-Res Farewell to Pluto — NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute · NASA Image Library

Images from open archives · credit shown per image