Object profile · EUROPA
Europa
Icy Galilean ocean-world candidate
A bright, fractured ice world with strong evidence for a salty ocean hidden below.
- Atlas data reviewed
- Editorial stage
- Published
- Visibility
- Public
Direct observationOfficial data mosaic. Gaps were filled with simulated color from nearby similar terrain, as disclosed by NASA.
NASA/JPL-Caltech/SETI Institute ↗What this world is
Europa's surface is ice, but Jupiter's changing tidal pull can flex and warm its interior. Magnetic evidence strongly favors an electrically conducting salty ocean below.
Why it looks this way now
The buried ocean is strongly inferred, not photographed. Europa Clipper is investigating whether environments below the surface could support life, not claiming life has been found.
Where it sits
The second Galilean moon, inside Ganymede's orbit and part of the Io-Europa-Ganymede resonance.
Swipe sideways to inspect the full map
Europa is 2 of 4 profiled Jupiter moons by distance, at a mean center distance of about 671,000 km.
The left panel locates Jupiter, dashed lines mark the scale change, and muted orbits and dots represent other profiled moons on the right. Io is the adjacent profiled moon inside; Ganymede is adjacent outside.
Read the numbers
Reference values retain their units, context, evidence state and published uncertainty.
Physical measurements
- Mean radiusglobal mean
- 1,560.8kmCalculated measurementThe mean radius is about 0.90 times the radius of Earth's Moon.
Irregular moons have no single true radius; the mean radius is an equal-volume comparison.
Published uncertainty: ± 0.3 km
JPL tabulated uncertainty for the adopted mean radius.
- Massglobal mean
- 4.798574E22kgCalculated 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
- 3.0130g/cm³Calculated measurementDenser than ice alone, requiring a large rocky and metallic interior beneath the water-rich exterior.
This is a whole-body average and cannot by itself prove the composition of every interior layer.
Published uncertainty: ± 0.0017 g/cm³
JPL tabulated uncertainty for the adopted mean density.
- Reference gravitysurface
- 1.3147m/s²Calculated measurementRepresentative surface gravity is about 13.4% 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
- -160°CScientific modelColder than Antarctic winter; surface water remains hard ice.
This is a representative surface value, not the temperature of the inferred buried ocean.
Approximate value
Representative surface temperature. Latitude, illumination and time produce meaningful variation.
Orbit and rotation
- Average distancesystem reference
- 671,000kmCalculated measurementThis is a representative center-to-center distance between Europa and Jupiter.
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
- 3.551Earth 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
- 3.551Earth 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
Europa has an extremely tenuous oxygen atmosphere produced mainly by radiation breaking surface ice molecules apart.
- Molecular oxygenRelative abundance described; exact fraction not listed
Surface and interior
The leading model places an iron core and rocky mantle below a global salty ocean and fractured ice shell.
- 1Metallic core
A dense central core is inferred from size, mass and differentiated-interior models.
Scientific model - 2Rocky mantle
A silicate mantle likely supplies heat and chemical interactions at the ocean floor.
Scientific model - 3Inferred salty ocean
Magnetic induction and geology strongly support a conductive liquid layer, but its exact depth is modeled.
Scientific model - 4Fractured water-ice shell
Direct images show ridges, bands and young terrain across a water-ice surface.
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
Galileo
Galileo made 12 close Europa flybys and returned imaging and magnetic evidence central to the ocean hypothesis.
Official mission ↗- Solid-State Imaging cameraImages the limb, terrain, color differences and time-dependent surface changes.
- Spacecraft radio scienceMeasures Doppler and range changes that constrain trajectory, gravity and mass.
- Near-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
Europa Facts
- 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
Europa's Stunning Surface
- Source updated
- No source update date published
- Access checked
- 2026-07-31
- 04
NASA Science · official-page
Galileo 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.