Moon
Iapetus
- Type
- Moon
- Diameter
- 1,471 km
NASA/JPL/Space Science Institute · NASA media (public domain)
Overview
Scientific overview
Iapetus is a moon orbiting Saturn.
Physical characteristics
- Mass
- 0.002 ×10²⁴ kg
- Diameter
- 1,471 km
- Radius
- 735.6 km
- Density
- 1.083 g/cm³
- Surface gravity
- 0.22 m/s² · derived
- Escape velocity
- 0.6 km/s · derived
- Albedo
- 0.6
- Magnitude
- 11
Derived values
Computed from source-backed inputs via standard formulae — not observations. Every input and constant is traced below.
- Escape velocity0.6 km/sderived
Formula & inputs
Formula: v = √(2GM / r) (v1.0.0, impl v1.0.0)
Inputs:
- mass1e24Kg = 0.00181 ×10²⁴ kg · NASA
- radiusKm = 735.6 km · NASA
Assumptions: G = 6.674e-11 m³ kg⁻¹ s⁻² (CODATA 2018)
Limitations: Assumes a spherical, non-rotating body.; Inputs carry no catalogued uncertainty, so none is propagated.
Uncertainty: not propagated (inputs carry no catalogued uncertainty)
Computed as of 2026-06-29.
- Surface gravity0.22 m/s²derived
Formula & inputs
Formula: g = GM / r² (v1.0.0, impl v1.0.0)
Inputs:
- mass1e24Kg = 0.00181 ×10²⁴ kg · NASA
- radiusKm = 735.6 km · NASA
Assumptions: G = 6.674e-11 m³ kg⁻¹ s⁻² (CODATA 2018)
Limitations: Assumes a spherical, non-rotating body.; Inputs carry no catalogued uncertainty, so none is propagated.
Uncertainty: not propagated (inputs carry no catalogued uncertainty)
Computed as of 2026-06-29.
Scale
Compared to Earth
Iapetus is 8.7× smaller than Earth
1,471 km across · Earth is 12,742 km
Gallery
Cloaking Iapetus
Darkness sweeps over Iapetus as the Cassini spacecraft watches the shadow of Saturn B ring engulf the dichotomous moon.
2007
NASA/JPL/Space Science Institute · NASA media (public domain)
Observation
How this was captured
- Source
- NASA
- Observation date
- 2010-01-06
Sources
The primary and reference sources this topic draws on.
- NASANational Aeronautics and Space Administration
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.
- NASA JPLJet Propulsion Laboratory / Solar System Dynamics
Orbital data, ephemerides, and small-body parameters for planets, asteroids, and comets.