Moon
Io
- Type
- Moon
- Diameter
- 3,643 km
NASA/JPL · NASA media (public domain)
Overview
Scientific overview
Io is a moon orbiting Jupiter.
Physical characteristics
- Mass
- 0.089 ×10²⁴ kg
- Diameter
- 3,643 km
- Radius
- 1,821.6 km
- Density
- 3.528 g/cm³
- Surface gravity
- 1.80 m/s² · derived
- Escape velocity
- 2.6 km/s · derived
- Albedo
- 0.63
- Magnitude
- 5.02
Derived values
Computed from source-backed inputs via standard formulae — not observations. Every input and constant is traced below.
- Escape velocity2.6 km/sderived
Formula & inputs
Formula: v = √(2GM / r) (v1.0.0, impl v1.0.0)
Inputs:
- mass1e24Kg = 0.0893 ×10²⁴ kg · NASA
- radiusKm = 1821.6 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 gravity1.80 m/s²derived
Formula & inputs
Formula: g = GM / r² (v1.0.0, impl v1.0.0)
Inputs:
- mass1e24Kg = 0.0893 ×10²⁴ kg · NASA
- radiusKm = 1821.6 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
Io is 3.5× smaller than Earth
3,643 km across · Earth is 12,742 km
Gallery
Juno Getting Closer to Jovian Moon Io
This image of the Jovian moon Io was generated using data collected by the JunoCam imager aboard NASA's Juno spacecraft during a flyby of the moon on March 1, 2023.
2023
Image data: NASA/JPL-Caltech/SwRI/MSSS Image processing: Kevin M. Gill (CC BY) · NASA media (public domain)
Observation
How this was captured
- Source
- NASA
- Observation date
- 1998-12-05
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.