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Object profile · DIONE

Dione

Fractured icy moon of Saturn

An icy world where Cassini turned mysterious bright wisps into a readable network of tectonic cliffs and canyons.

Atlas data reviewed
Editorial stage
Published
Visibility
Public
Cassini grayscale full-disk mosaic of Dione showing bright icy terrain, craters and long fractures.Direct observation
Cassini clear-filter frames combined into a detailed full view of Dione.

Official grayscale data mosaic assembled from spacecraft frames; brightness does not map composition by itself.

NASA/JPL/Space Science Institute ↗
Vastward explanation

What this world is

Voyager made Dione's trailing side look painted with white wisps. Cassini flew closer and showed that the lines are bright canyon walls exposed when darker material falls away.

Why it looks this way now

Cassini directly mapped craters, smooth plains and fracture cliffs, proving that Dione was tectonically active in the past. The timing and energy source of that activity remain model-dependent.

02

Where it sits

A mid-sized Saturnian moon accompanied by the small co-orbital moons Helene and Polydeuces near its Lagrange points.

How to read this mapTwo-scale location · Solar System to the Saturn moons

Swipe sideways to inspect the full map

Two-scale location · Solar System to the Saturn moonsThe left panel places Saturn in planetary order; the right places Dione among the profiled Saturn moon orbits.Scale one · Solar SystemSaturnPlanet 6 from the SunSunScale two · Saturn moon systemSaturnDioneProfiled orbit 4 of 9Mean distance · 377,700 km
Blue marks the current moon and orbit

Dione is 4 of 9 profiled Saturn moons by distance, at a mean center distance of about 377,700 km.

Muted lines and dots show system context

The left panel locates Saturn, dashed lines mark the scale change, and muted orbits and dots represent other profiled moons on the right. Tethys is the adjacent profiled moon inside; Rhea is adjacent outside.

The figure uses two linked scales and compares only the same-system moons currently profiled by Vastward; orbit spacing, body sizes and marker positions are compressed for teaching.
03

Read the numbers

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

Physical measurements

Mean radiusglobal mean
561.4kmCalculated measurementThe mean radius is about 0.324 times the radius of Earth's Moon.

Irregular moons have no single true radius; the mean radius is an equal-volume comparison.

Published uncertainty: ± 0.4 km

JPL tabulated uncertainty for the adopted mean radius.

Massglobal mean
1.095487E21kgCalculated 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
1.4781g/cm³Calculated measurementDenser than Tethys and Rhea, indicating a larger rock fraction mixed with the ice.

This is a whole-body average and cannot by itself prove the composition of every interior layer.

Published uncertainty: ± 0.0032 g/cm³

JPL tabulated uncertainty for the adopted mean density.

Reference gravitysurface
0.231989m/s²Calculated measurementRepresentative surface gravity is about 2.36% 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
-186°CDirect observationNear -186 °C, surface ice is hard enough to preserve tall fracture scarps and ancient craters.

The displayed average cannot represent every illuminated slope, canyon wall and shadow.

Approximate value

NASA reports an average temperature near 87 K (-186 °C). Local sunlit and shadowed surfaces differ.

Orbit and rotation

Average distancesystem reference
377,700kmCalculated measurementThis is a representative center-to-center distance between Dione 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
2.736916Earth 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
2.736916Earth 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.

04

Atmosphere and inside

Atmosphere

Dione has no substantial persistent atmosphere in the ordinary sense; its surface is exposed directly to space.

Surface and interior

Dione combines a modelled rock-and-ice interior with a directly observed crust recording impacts and ancient tectonic extension.

  1. 1
    Modelled rock-and-ice interior

    Bulk density requires more rock than Tethys, but current measurements do not uniquely map the deep layers.

    Scientific model
  2. 2
    Fractured ice crust

    Cassini images directly show bright fault scarps, canyons, plains and heavily cratered terrains.

    Direct observation
05

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.

  1. 01

    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.

    Direct observation
  2. 02

    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.

    Calculated measurement
  3. 03

    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.

    Direct observation
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

Completed

Cassini-Huygens

Cassini resolved Dione's wispy terrain into fracture cliffs and constrained its mass, shape and past tectonic history.

Official mission ↗
Instruments
  • 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.
08

Official source trail

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

  1. 01

    NASA Science · official-page

    Dione

    Source updated
    No source update date published
    Access checked
    2026-07-31
    Open official source ↗
  2. 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
    Open official source ↗
  3. 03

    NASA Science Photojournal · image

    Dione in Full View

    Source updated
    No source update date published
    Access checked
    2026-07-31
    Open official source ↗
  4. 04

    NASA Science · official-page

    Cassini mission

    Source updated
    No source update date published
    Access checked
    2026-07-31
    Open official source ↗
09

Continue exploring

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

Available now

Understand moon systems

Place Dione back inside Saturn's moon system and connect orbit, tides and resonance.

academy
Relationship reserved

Compare the major moons

Compare size, density, gravity and orbit without treating similar colors as identical composition.

lab