Object profile · ENCELADUS
Enceladus
Active icy ocean moon
A small bright moon that vents water-rich material from a global ocean into space.
- Atlas data reviewed
- Editorial stage
- Published
- Visibility
- Public
Direct observationOfficial false-color spectral mosaic. Red-tinted areas highlight infrared signatures of fresh crystalline ice, not visible redness.
NASA/JPL-Caltech/University of Arizona/LPG/CNRS/University of Nantes/Space Science Institute ↗What this world is
Enceladus offers a rare shortcut to a hidden ocean: fractures near the south pole spray water vapor, ice grains, salts and organics into space where a spacecraft can sample them.
Why it looks this way now
Cassini directly sampled the plume and strongly established a global salty ocean with hydrothermal activity. No life has been detected.
Where it sits
An inner Saturnian moon embedded in the E ring, which its plumes help replenish.
Swipe sideways to inspect the full map
Enceladus is 2 of 9 profiled Saturn moons by distance, at a mean center distance of about 238,000 km.
The left panel locates Saturn, dashed lines mark the scale change, and muted orbits and dots represent other profiled moons on the right. Mimas is the adjacent profiled moon inside; Tethys is adjacent outside.
Read the numbers
Reference values retain their units, context, evidence state and published uncertainty.
Physical measurements
- Mean radiusglobal mean
- 252.1kmCalculated measurementThe mean radius is about 0.145 times the radius of Earth's Moon.
Irregular moons have no single true radius; the mean radius is an equal-volume comparison.
Published uncertainty: ± 0.2 km
JPL tabulated uncertainty for the adopted mean radius.
- Massglobal mean
- 1.080319E20kgCalculated 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
- 1.6097g/cm³Calculated measurementDenser than pure water ice, showing that a rocky component is mixed into the small moon.
This is a whole-body average and cannot by itself prove the composition of every interior layer.
Published uncertainty: ± 0.0038 g/cm³
JPL tabulated uncertainty for the adopted mean density.
- Reference gravitysurface
- 0.11345m/s²Calculated measurementRepresentative surface gravity is about 1.16% 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
- -201°CScientific modelMost of the surface is near -200 °C, but active fractures are locally much warmer.
The reference is a broad surface value and does not erase measured south-polar hotspots.
Approximate value
Representative surface value. Active south-polar fractures contain much warmer local regions.
Orbit and rotation
- Average distancesystem reference
- 238,000kmCalculated measurementThis is a representative center-to-center distance between Enceladus and Saturn.
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
- 1.370Earth 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
- 1.370Earth 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
A very thin, localized water-vapor environment is continuously supplied by south-polar plumes.
- Water vaporRelative abundance described; exact fraction not listed
Surface and interior
A fractured ice shell surrounds a global salty ocean above a porous rocky core, where water-rock reactions may occur.
- 1Porous rocky core
Gravity and libration data support a low-density rocky core interacting with liquid water.
Scientific model - 2Global salty ocean
Libration, gravity and plume chemistry strongly support a global liquid-water layer.
Scientific model - 3Fractured ice shell
Direct images and thermal maps show a bright crust split by active south-polar tiger stripes.
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
Cassini-Huygens
Cassini discovered the plume, flew through it, measured salts and organics, and established a global ocean model.
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.
- Visual and Infrared Mapping SpectrometerSeparates 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
Enceladus Science
- 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
Enceladus in the Infrared
- Source updated
- No source update date published
- Access checked
- 2026-07-31
- 04
NASA Science · official-page
Cassini 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.