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Object profile · HYPERION

Hyperion

Chaotically tumbling porous moon of Saturn

A sponge-looking rubble pile whose orbit with Titan helps drive an unpredictable tumble.

Atlas data reviewed
Editorial stage
Published
Visibility
Public
Cassini false-color view of irregular Hyperion, covered in deep sponge-like craters with bright walls and dark floors.Direct observation
Cassini combined infrared, green and ultraviolet frames to expose subtle material differences across Hyperion.

Official false-color spacecraft observation. Hues are enhanced for composition contrast and are not what unaided human vision would see.

NASA/JPL-Caltech/Space Science Institute ↗
Vastward explanation

What this world is

Hyperion is not a compact ball. Its weak gravity leaves a porous body where impacts compress the surface more than they blast material outward, preserving deep sponge-like craters.

Why it looks this way now

Cassini directly imaged bright water-ice crater walls, dark reddish crater floors and an irregular shape. Low density supports a porous rubble-pile model, while Titan's resonance and the eccentric orbit help explain chaotic rotation.

02

Where it sits

An outer regular moon between Titan and Iapetus, following an eccentric orbit about 1.5 million kilometres from Saturn.

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 Hyperion among the profiled Saturn moon orbits.Scale one · Solar SystemSaturnPlanet 6 from the SunSunScale two · Saturn moon systemSaturnHyperionProfiled orbit 7 of 9Mean distance · 1,500,000 km
Blue marks the current moon and orbit

Hyperion is 7 of 9 profiled Saturn moons by distance, at a mean center distance of about 1,500,000 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. Titan is the adjacent profiled moon inside; Iapetus 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
135kmCalculated measurementThe mean radius is about 0.078 times the radius of Earth's Moon.

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

Published uncertainty: ± 4 km

JPL tabulated uncertainty for the adopted mean radius.

Massglobal mean
5.550994E18kgCalculated 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
0.5386g/cm³Calculated measurementOnly a little more than half the density of water, consistent with an ice-rich body containing more than 40 percent empty space.

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

Published uncertainty: ± 0.0479 g/cm³

JPL tabulated uncertainty for the adopted mean density.

Reference gravitysurface
0.020329m/s²Calculated measurementRepresentative surface gravity is about 0.21% 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
-180°CDirect observationIts average surface is near -180 °C; bright crater walls and dark floors can respond differently to sunlight.

This is a representative average from Cassini-era interpretation, not one temperature for every crater and time of day.

Approximate value

NASA reports a representative average near 93 K (-180 °C). Illumination, crater depth and local material change the actual surface temperature.

Orbit and rotation

Average distancesystem reference
1,500,000kmCalculated measurementThis is a representative center-to-center distance between Hyperion 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
13Earth daysCalculated measurementInstead of keeping one face toward Saturn, Hyperion changes orientation unpredictably as it moves along its orbit.

The displayed value is a representative timescale, not a precise repeating day, because the rotation is chaotic.

Approximate value

A roughly 13-day rotational timescale is shown for orientation. Hyperion tumbles chaotically, so it has no single repeatable orientation cycle like a tidally locked moon.

Orbital periodrelative to distant stars
21.2766Earth 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

Hyperion has no persistent atmosphere; Cassini instead detected an electrically charged surface environment.

Surface and interior

The safest model is a porous ice-rich rubble pile beneath a directly observed, deeply cratered surface—not a solid sponge with known internal tunnels.

  1. 1
    Porous ice-rich rubble interior

    Low density is consistent with loosely compacted ice and rock containing more than 40 percent void space, but the arrangement is a model rather than a direct image.

    Scientific model
  2. 2
    Deeply cratered ice-rich surface

    Cassini images directly show bright ice-rich crater walls, darker floors and unusually deep, sharply preserved cavities.

    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 completed the close 2005 flyby, resolving Hyperion's porous-looking crater record, surface colors and chaotic rotational state.

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

    Hyperion

    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

    Saturn's Battered Moon Hyperion, PIA07740

    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 Hyperion 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