Object profile · TRITON
Triton
Retrograde captured ice world
Neptune's largest moon, orbiting backward with a young icy surface and observed nitrogen plumes.
- Atlas data reviewed
- Editorial stage
- Published
- Visibility
- Public
Direct observationOfficial synthesized-color mosaic. Voyager 2 closely imaged only part of Triton, and the displayed colors come from combined filters.
NASA/JPL/USGS ↗What this world is
Triton probably began as a Kuiper Belt world and was captured by Neptune. The capture reshaped Neptune's earlier moon system and will eventually draw Triton inward.
Why it looks this way now
Voyager 2 directly saw a young surface and dark plume deposits during one flyby in 1989. Present-day activity and any buried ocean remain uncertain.
Where it sits
A large moon on a retrograde, inclined orbit, unlike the regular moons that formed in place around their planets.
Swipe sideways to inspect the full map
Triton is 1 of 1 profiled Neptune moons by distance, at a mean center distance of about 354,760 km.
The left panel locates Neptune, dashed lines mark the scale change, and muted orbits and dots represent other profiled moons on the right. This is the innermost profiled moon in the system; it is the outermost profiled moon in the system.
Read the numbers
Reference values retain their units, context, evidence state and published uncertainty.
Physical measurements
- Mean radiusglobal mean
- 1,352.6kmCalculated measurementThe mean radius is about 0.78 times the radius of Earth's Moon.
Irregular moons have no single true radius; the mean radius is an equal-volume comparison.
Published uncertainty: ± 2.4 km
JPL tabulated uncertainty for the adopted mean radius.
- Massglobal mean
- 2.140293E22kgCalculated measurementMass is not read from a scale. Motion under gravity constrains GM, from which mass is derived.
Calculated from JPL GM with a conventional gravitational constant, then rounded for display.
Approximate value
Derived from JPL's gravitational parameter GM and a conventional gravitational constant, then rounded.
- Mean densityglobal mean
- 2.0649g/cm³Calculated measurementDenser than many icy moons, indicating a substantial rocky fraction mixed with volatile ices.
This is a whole-body average and cannot by itself prove the composition of every interior layer.
Published uncertainty: ± 0.011 g/cm³
JPL tabulated uncertainty for the adopted mean density.
- Reference gravitysurface
- 0.7808m/s²Calculated measurementRepresentative surface gravity is about 8.0% of Earth's.
Shape, terrain and local mass distribution make real gravity vary by location.
Approximate value
Calculated from the adopted GM and mean radius. Irregular shape and local terrain can change the actual value.
- Temperaturesurface
- -235°CDirect observationAt about -235 °C, nitrogen itself freezes across much of the surface.
Voyager 2 measured this extreme cold during the only close flyby, so seasonal changes remain poorly sampled.
Approximate value
Voyager 2 surface-temperature measurement reported by NASA; coverage came from one 1989 flyby.
Orbit and rotation
- Average distancesystem reference
- 354,760kmCalculated measurementThis is a representative center-to-center distance between Triton and Neptune.
The real distance changes around an elliptical orbit.
Approximate value
Rounded orbital distance from the moon center to the planet center. The real orbit is not a perfect circle.
- Rotation periodrelative to distant stars
- 5.877Earth daysCalculated measurementTidal locking makes one rotation take nearly the same time as one orbit around the planet.
This is a sidereal rotation, not a local sunrise-to-sunrise solar day.
Approximate value
Rounded synchronous rotation period. The same hemisphere normally faces the primary planet.
- Orbital periodrelative to distant stars
- 5.877Earth daysCalculated measurementThis reports duration; Triton's direction is opposite Neptune's rotation.
A rounded sidereal period is used for the beginner-facing display.
Approximate value
Rounded sidereal period. Triton travels opposite Neptune's rotation; the positive number reports duration, not direction.
Atmosphere and inside
Atmosphere
Triton has a very thin nitrogen atmosphere with methane. Surface frost and seasonal sunlight exchange material with it.
- NitrogenRelative abundance described; exact fraction not listed
- MethaneRelative abundance described; exact fraction not listed
Surface and interior
A dense rocky core is probably wrapped in volatile-rich ice. A buried liquid layer is plausible but not confirmed.
- 1Rock-metal core
Density and differentiation models imply a substantial rocky central fraction.
Scientific model - 2Volatile-rich icy mantle
Models allow water ice and other volatile-rich layers, with a possible liquid zone that is not confirmed.
Scientific model - 3Nitrogen-frost surface
Voyager directly observed bright icy terrain, cantaloupe textures and dark plume deposits.
Direct observation
How we know
Images constrain size, orbital and radio tracking constrain GM, and spectra and thermal emission constrain materials. Every number retains its method and limitation.
- 01Direct observation
Spacecraft imaging and shape reconstruction
Repeated views reveal the limb, terrain, crater record and the shape used to estimate size.
Where this method stops
Lighting, viewing angle and incomplete coverage can hide topography. A mosaic is not a single untouched photograph.
- 02Calculated measurement
Radio tracking and orbital dynamics
Engineers measure spacecraft motion and moon orbits, solve for GM, and then derive mass and gravity.
Where this method stops
The result depends on trajectory coverage and a dynamical model. Very small moons leave weaker gravitational signatures.
- 03Direct observation
Spectroscopy and thermal sensing
The spectrum and thermal glow constrain surface materials, gases and representative temperature.
Where this method stops
A spectrum samples the visible surface or atmosphere. It does not directly photograph deep interior layers.
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
Voyager 2
Voyager 2 completed the only close Triton flyby, imaging its young terrain, measuring extreme cold and observing active plumes.
Official mission ↗- Imaging Science SubsystemImages the limb, terrain, color differences and time-dependent surface changes.
- Spacecraft radio scienceMeasures Doppler and range changes that constrain trajectory, gravity and mass.
- Infrared Interferometer Spectrometer and RadiometerSeparates light by wavelength to constrain composition, gases and temperature.
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
Triton
- Source updated
- No source update date published
- Access checked
- 2026-07-31
- 02
NASA Jet Propulsion Laboratory, Solar System Dynamics · dataset
Planetary Satellite Physical Parameters
- Source updated
- No source update date published
- Access checked
- 2026-07-31
- 03
NASA Science Photojournal · image
Global Color Mosaic of Triton
- Source updated
- No source update date published
- Access checked
- 2026-07-31
- 04
NASA Science · official-page
Voyager mission
- 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.