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Object profile · NEPTUNE

Neptune

Ice giant

The outermost major planet, a cold blue world with fast winds, changing storms and a warm hidden interior.

Atlas data reviewed
Editorial stage
Published
Visibility
Public
A processed Voyager 2 portrait of Neptune as a blue sphere with pale cloud bands and bright high clouds.Direct observation
Voyager 2 narrow-angle camera portrait from filtered observations during the 1989 encounter.

Processed spacecraft colour image. Filter combinations and contrast shape the familiar blue appearance; it is not one unaltered exposure or a size and distance scale.

NASA/Caltech ↗
Vastward explanation

What this world is

Neptune receives very little sunlight, yet its atmosphere is remarkably active. Bright methane-ice clouds race above dark storm systems, and the planet gives off more energy than it absorbs from the Sun. Like Uranus, it has no solid surface.

Why it looks this way now

Residual formation heat and ongoing contraction likely help drive convection and weather, but the detailed energy path is modeled. Methane absorbs red wavelengths, while haze and deeper absorbers also influence colour. Modern reprocessing shows the familiar vivid blue can overstate its visual difference from Uranus.

02

Where it sits

Neptune is the eighth planet from the Sun, averaging about 4.5 billion kilometres or 30 astronomical units away. One orbit lasts almost 165 Earth years.

How to read this mapPlanetary order · 8 of 8 from the Sun

Swipe sideways to inspect the full map

Planetary order · 8 of 8 from the SunEight compressed orbits surround the Sun. Orbit 8, belonging to Neptune, is highlighted in blue, with all planets ordered below.SunPosition 8 from the SunNeptuneMercuryVenusEarthMarsJupiterSaturnUranusNeptune
Blue marks the current planet

The blue orbit, marker and name locate Neptune without implying its live position today.

Neighboring worlds provide order context

Uranus is immediately inside; it is the outermost planet. The lower sequence preserves all eight positions.

The figure preserves the eight-planet order and orbital hierarchy; distances, orbit spacing, body sizes and marker positions are compressed for teaching rather than shown live.
03

Read the numbers

Reference values retain their units, context, evidence state and published uncertainty.

Physical measurements

Mean radiusglobal mean
24,622kmCalculated measurementAbout 3.9 Earth radii.

An atmospheric reference radius, not solid ground.

Published uncertainty: ± 19 km

JPL tabulated uncertainty at an adopted atmospheric reference level.

Massglobal mean
1.024092E26kgCalculated measurementAbout 17 Earth masses.

Moon orbits and Voyager tracking constrain total mass.

Published uncertainty: ± 4.8E21 kg

Converted from the uncertainty in the JPL 10^24 kilogram table.

Mean densityglobal mean
1.638g/cm³Calculated measurementThe densest of the four giant planets.

Bulk density still does not uniquely specify the internal mixture.

Published uncertainty: ± 0.004 g/cm³

Calculated from adopted mass and volume.

Reference gravityequatorial reference
11.15m/s²Calculated measurementAbout 1.14 times Earth's at the reference level.

There is no solid surface to stand on.

No uncertainty published in this source table

Reference gravity at an adopted atmospheric level; Neptune has no solid surface.

Temperaturevisible cloud level
-214°CCalculated measurementA representative value near the one-bar level.

Higher clouds and deeper layers have different temperatures.

Approximate value

Representative temperature near the one-bar atmospheric level; altitude, latitude and season matter.

Temperaturedeep interior model
5,127°CScientific modelA modeled deep value, not a probe reading.

Composition and thermal histories remain uncertain.

Approximate value

Representative modeled deep-interior temperature near 5,400 kelvin; no direct probe has reached this layer.

Orbit and rotation

Average distancerelative to the Sun
4,500,000,000kmCalculated measurementAbout 30 times Earth's solar distance.

Sunlight is roughly one 900th as intense.

Approximate value

Rounded average distance, about 30 astronomical units.

Rotation periodrelative to distant stars
0.67125Earth daysCalculated measurementAbout 16 hours 7 minutes.

Visible winds rotate differently from the adopted bulk period.

No uncertainty published in this source table

Adopted bulk rotation period; visible clouds rotate differentially.

Orbital periodrelative to the Sun
164.79132Earth yearsCalculated measurementNeptune completed its first full orbit since discovery in 2011.

A year lasts almost 165 Earth years.

No uncertainty published in this source table

Sidereal orbital period from astrometry and dynamical ephemerides.

04

Atmosphere and inside

Atmosphere

Hydrogen and helium dominate, with methane and trace gases. Strong winds, high clouds and transient dark vortices occur across a deep atmosphere that grades into dense fluid.

HydrogenRelative abundance described; exact fraction not listed
HeliumRelative abundance described; exact fraction not listed
Methane and trace gasesRelative abundance described; exact fraction not listed

Surface and interior

Models place a volatile-rich conducting fluid layer above a denser core region. Gravity, magnetic and heat data constrain possibilities but do not directly image the interior.

No solid surface: layers transition gradually as pressure and temperature rise.

  1. 1
    Dense core region

    Models allow a compact rock-and-metal-rich centre, but its boundary is not directly measured.

    Scientific model
  2. 2
    Hot volatile-rich fluid mantle

    Water, methane and ammonia components are modeled in a hot dense conducting mixture. Ice giant refers to elemental inventory, not frozen blocks.

    Scientific model
  3. 3
    Hydrogen-helium envelope

    A lighter outer envelope compresses gradually into dense fluid, with no solid landing surface.

    Scientific model
  4. 4
    Methane clouds and active weather

    Spacecraft and telescopes directly see bright high clouds, bands and changing dark vortices in the upper atmosphere.

    Direct observation
05

How we know

Voyager 2 supplied the sole close encounter. Filtered imaging, infrared spectra, radio tracking and occultations combine with long-term telescope monitoring and astrometry.

  1. 01

    Multifilter imaging

    Voyager 2 and telescopes record reflected light to track clouds, vortices, rings and limb geometry.

    Where this method stops

    Filter mapping and contrast processing alter appearance; a single 1989 flyby sampled a brief season.

    Direct observation
  2. 02

    Astrometry and flyby radio tracking

    Long-term sky positions establish the orbit; Voyager Doppler and moon motions constrain mass and gravity.

    Where this method stops

    One close flyby leaves the gravity field and rotation less precise than for planets with orbiters.

    Calculated measurement
  3. 03

    Infrared spectroscopy and radiometry

    Thermal and reflected spectra constrain gases, clouds, temperatures and the planet's strong internal heat output.

    Where this method stops

    Retrievals sense broad pressure layers and depend on cloud opacity and radiative-transfer models.

    Calculated measurement
  4. 04

    Interior and thermal-evolution modeling

    Mass, shape, gravity, magnetic field and emitted heat are tested against candidate compositions and histories.

    Where this method stops

    Sparse gravity harmonics permit multiple core sizes, mixing profiles and thermal histories.

    Scientific model
06

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.
07

Missions and instruments

Active

Voyager 2

The only spacecraft to visit Neptune, measuring its weather, rings, moons, gravity, magnetic field and plasma environment during the 1989 flyby.

Official mission ↗
Instruments
  • Voyager Imaging Science SubsystemFiltered visible-light images of Neptune, its weather, rings and moons.
  • Voyager radio scienceDoppler motion and occultations used for gravity, atmospheric profiles and ring structure.
  • Infrared Interferometer Spectrometer and RadiometerThermal spectra, temperatures and atmospheric energy balance.
08

Official source trail

Links below are the exact records used for this profile. Access dates are retained with the content.

  1. 01

    NASA Jet Propulsion Laboratory, Solar System Dynamics · dataset

    Planetary Physical Parameters

    Source updated
    No source update date published
    Access checked
    2026-07-30
    Open official source ↗
  2. 02

    NASA Science · official-page

    Neptune Facts

    Source updated
    2025-06-26
    Access checked
    2026-07-30
    Open official source ↗
  3. 03

    NASA Science · image

    Neptune (Voyager 2)

    Source updated
    2025-08-28
    Access checked
    2026-07-30
    Open official source ↗
  4. 04

    NASA Science · official-page

    Voyager 2

    Source updated
    2026-01-07
    Access checked
    2026-07-30
    Open official source ↗
09

Continue exploring

Atlas is a starting point. Use these relationships to move into explanation, experiment and mission thinking.

Relationship reserved

Drive weather far from the Sun

Balance weak sunlight against internal heat and atmospheric motion.

lab
Relationship reserved

Rebuild Neptune's colour

Compare filter mappings and separate spectral evidence from presentation.

lab
Relationship reserved

Compare the ice giants

Ask why similar sizes can hide different heat flows and histories.

lab