Object profile · PLUTO
Pluto
Dwarf planet · Kuiper Belt
A geologically diverse ice world whose heart-shaped basin reshaped our idea of small planets.
- Atlas data reviewed
- Editorial stage
- Published
- Visibility
- Public
Direct observationOfficial NASA mission observations processed in enhanced color. Relative separation is not to scale.
NASA/Johns Hopkins APL/Southwest Research Institute ↗What this world is
Pluto is smaller than Earth's Moon but surprisingly complex. Nitrogen glaciers flow, water-ice mountains rise, haze layers wrap the world, and Charon is so large that the pair behaves like a double system.
Why it looks this way now
New Horizons has passed far beyond Pluto. Its flyby archive remains the only close-range dataset, while telescopes track seasonal change.
Where it sits
Pluto follows an inclined, eccentric orbit in the Kuiper Belt and shares a barycentric dance with its large moon Charon.
Swipe sideways to inspect the full map
Pluto orbits the Sun directly at a mean distance of about 39.236 AU; the marker is not a live position.
Neptune provides the outer-planet reference. The shaded zone shows the broad relationship to the Kuiper Belt, while muted dots are other profiled outer-system dwarf planets; horizontal distance is heavily compressed.
Read the numbers
Reference values retain their units, context, evidence state and published uncertainty.
Physical measurements
- Mean radiusglobal mean
- 1,188.3kmCalculated measurementA little smaller than Earth's Moon.
A global reference radius reconstructed from imaging, thermal data or occultation.
No uncertainty published in this source table
The selected summary source does not publish a compact uncertainty for this reference value.
- Massglobal mean
- 1.303E22kgCalculated measurementFar below Earth's mass, yet enough gravity to become rounded.
Calculated from the motion of a spacecraft, moon or dynamical system.
No uncertainty published in this source table
The selected summary source does not publish a compact uncertainty for this reference value.
- Mean densityglobal mean
- 1.854g/cm³Calculated measurementA clue to the relative mixture of rock, water ice and voids.
Density is calculated from mass and volume; it does not reveal a unique interior by itself.
No uncertainty published in this source table
The selected summary source does not publish a compact uncertainty for this reference value.
- Reference gravitysurface
- 0.62m/s²Calculated measurementOnly a few percent of Earth's surface gravity.
A reference value derived from mass and radius.
No uncertainty published in this source table
The selected summary source does not publish a compact uncertainty for this reference value.
- Temperaturesurface
- -240°CScientific modelCold enough for volatile compounds to remain as surface ice.
A model-supported representative temperature, not a thermometer reading on the ground.
Approximate value
Representative equilibrium or surface temperature; local and seasonal conditions vary.
Orbit and rotation
- Average distancerelative to the Sun
- 39.236AUCalculated measurementDozens of times farther from the Sun than Earth.
The semi-major-axis reference summarizes an orbit whose actual distance changes.
No uncertainty published in this source table
The selected summary source does not publish a compact uncertainty for this reference value.
- Rotation periodrelative to distant stars
- 153.2928hCalculated measurementPluto turns in the retrograde direction once every 6.4 Earth days.
The displayed magnitude is a sidereal rotation period; the text preserves Pluto's retrograde direction.
No uncertainty published in this source table
The selected summary source does not publish a compact uncertainty for this reference value.
- Orbital periodrelative to the Sun
- 247.94Earth yearsCalculated measurementOne full season cycle lasts many human lifetimes.
Calculated from long-baseline astrometry and a fitted heliocentric orbit.
No uncertainty published in this source table
The selected summary source does not publish a compact uncertainty for this reference value.
Atmosphere and inside
Atmosphere
Pluto carries a thin nitrogen atmosphere with methane and carbon monoxide. It expands nearer the Sun and may partly freeze onto the surface farther away.
- NitrogenRelative abundance described; exact fraction not listed
- Methane and carbon monoxideRelative abundance described; exact fraction not listed
Surface and interior
A rock-rich interior and thick water-ice shell are inferred. The possibility of a subsurface ocean remains under investigation.
- 1Rocky core model
Mass, radius and composition models imply a rock-rich interior, but no seismometer has sampled it.
Scientific model - 2Water-ice shell
Rigid water ice forms Pluto's bedrock and mountains; a buried ocean remains a scientific possibility.
Scientific model - 3Volatile-ice surface
New Horizons mapped nitrogen, methane and carbon-monoxide ices, glaciers, mountains and haze.
Direct observation
How we know
Size comes from imaging, thermal data or occultation; orbit and rotation from repeated positions and brightness; mass only when gravity leaves a measurable trace.
- 01Calculated measurement
Spacecraft shape reconstruction
Images from changing viewpoints trace the limb and reconstruct global shape.
Where this method stops
Image coverage and viewing geometry are uneven.
- 02Calculated measurement
Gravity from orbital motion
The motion of a moon or spacecraft reveals the central body's gravitational parameter.
Where this method stops
The solution depends on orbit coverage and a dynamical model.
- 03Calculated measurement
Thermal radiometry and spectroscopy
Brightness at visible, infrared and thermal wavelengths constrains temperature, reflectivity and surface ices.
Where this method stops
Temperature and size can trade off against albedo, roughness and thermal assumptions.
- 04Calculated measurement
Long-baseline astrometry
Repeated sky positions over years are fitted to a heliocentric orbit.
Where this method stops
Long-period distant objects need many years of observations and future values remain predictions.
- 05Calculated measurement
Rotational light curve
Repeating brightness changes reveal a candidate rotation period.
Where this method stops
Shape, surface markings and viewing angle can create aliases or double-peaked solutions.
Evidence key
- Direct observation
- An instrument or sample recorded the phenomenon, with processing still disclosed.
- Calculated measurement
- Observed motion or signal is converted into a physical quantity using equations and reference constants.
- Scientific model
- A tested interpretation that fits observations but is not directly imaged or sampled.
- Vastward explanation
- Original beginner-facing synthesis, traceable to the source records but not itself a measurement.
- Artist visualization
- An interpretive image, not observational evidence.
Missions and instruments
New Horizons
The 2015 flyby transformed Pluto from a point of light into a mapped world with active geology, atmosphere and moons.
Official mission ↗- LORRIHigh-resolution grayscale geology and navigation images.
- Ralph MVIC and LEISAColor, surface composition and infrared ice signatures.
- REXAtmospheric temperature and pressure through radio occultation.
Official source trail
Links below are the exact records used for this profile. Access dates are retained with the content.
- 01
NASA Science · official-page
Pluto Facts
- Source updated
- No source update date published
- Access checked
- 2026-07-31
- 02
NASA National Space Science Data Center · dataset
Pluto Fact Sheet
- Source updated
- No source update date published
- Access checked
- 2026-07-31
- 03
NASA Science · official-page
New Horizons
- Source updated
- No source update date published
- Access checked
- 2026-07-31
- 04
NASA Science · image
Pluto and Charon (New Horizons)
- Source updated
- No source update date published
- Access checked
- 2026-07-31
Continue exploring
Atlas is a starting point. Use these relationships to move into explanation, experiment and mission thinking.
Why is it a dwarf planet?
Use Pluto to separate roundness, orbit and orbital clearing—the three ideas behind the classification.
academyCompare the small worlds
Place radius, density and sunlight side by side without pretending every value is equally certain.
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