Object profile · OBERON
Oberon
Outer, heavily cratered major moon of Uranus
The outermost major Uranian moon, preserving old craters, dark crater floors and a mountain rising at the limb.
- Atlas data reviewed
- Editorial stage
- Published
- Visibility
- Public
Direct observationOfficial reconstructed-color spacecraft image. Features smaller than about 12 km are unresolved, and only one viewing geometry is represented.
NASA/JPL ↗What this world is
Oberon's surface is an old impact record. Some craters have bright rays, some floors are unusually dark, and a roughly 6 km mountain is visible at the edge of the Voyager image.
Why it looks this way now
Voyager 2 directly recorded the cratered surface and mountain. A 2023 thermal model permits a residual briny ocean, while current activity and the dark crater material remain unresolved.
Where it sits
The outermost and second-largest of Uranus' five major moons, beyond Titania.
Swipe sideways to inspect the full map
Oberon is 5 of 5 profiled Uranus moons by distance, at a mean center distance of about 583,511 km.
The left panel locates Uranus, dashed lines mark the scale change, and muted orbits and dots represent other profiled moons on the right. Titania is the adjacent profiled moon inside; 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
- 761.4kmCalculated measurementThe mean radius is about 0.438 times the radius of Earth's Moon.
Irregular moons have no single true radius; the mean radius is an equal-volume comparison.
Published uncertainty: ± 2.6 km
JPL tabulated uncertainty for the adopted mean radius.
- Massglobal mean
- 3.075978E21kgCalculated 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
- 1.6640g/cm³Calculated measurementSimilar to Titania within uncertainty, consistent with a mixed rocky and water-rich body.
This is a whole-body average and cannot by itself prove the composition of every interior layer.
Published uncertainty: ± 0.05 g/cm³
JPL tabulated uncertainty for the adopted mean density.
- Reference gravitysurface
- 0.35413m/s²Calculated measurementRepresentative surface gravity is about 3.61% 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
- -188°CScientific modelThis is a broad sunlit reference, not the temperature of every crater floor and shadow.
Sparse thermal sampling and extreme seasons leave the full temperature range poorly constrained.
Approximate value
Approximate sunlit upper reference near 85 K for Uranian moon terrain. It is not a measured global mean and does not represent polar night.
Orbit and rotation
- Average distancesystem reference
- 583,511kmCalculated measurementThis is a representative center-to-center distance between Oberon and Uranus.
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
- 13.463237Earth 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
- 13.463237Earth daysCalculated measurementThis reports the time for one orbit, not a claim that the path is perfectly circular.
A rounded sidereal period is used for the beginner-facing display.
Approximate value
Rounded sidereal orbital period.
Atmosphere and inside
Atmosphere
Oberon has no persistent atmosphere. Crater-floor darkness is a surface-material question, not weather.
Surface and interior
Oberon likely mixes rock and water-rich material beneath an ancient crust. A residual salty ocean is allowed by modeling, not confirmed.
- 1Modeled rock and water-rich interior
Density supports a mixed interior with a substantial rocky fraction and water-rich material.
Scientific model - 2Possible residual briny ocean
Thermal evolution modeling allows a salty liquid layer, but it has not been directly detected.
Scientific model - 3Ancient cratered ice-rich crust
Voyager images directly show bright-ray craters, dark crater floors and a mountain at the limb.
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 returned the only close Oberon image, revealing its ancient impact record, dark deposits and limb mountain.
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
Oberon
- 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
Oberon at Voyager Closest Approach
- 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
- 05
NASA Technical Reports Server · research-paper
Uranus Satellites: Surface Properties
- Source updated
- No source update date published
- Access checked
- 2026-07-31
- 06
NASA Jet Propulsion Laboratory · official-page
New Study of Uranus' Large Moons Shows 4 May Hold Water
- 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.