Current
Jupiter
139,822 kmmean diameter · kmmean diameter · twice JPL's mean radius
Planet & Moon Size Higher or Lower Game
Play the Planet and Moon Size Higher or Lower Game. Compare mean diameters of Solar System worlds using NASA JPL physical parameters.
Higher or Lower Game
Planet & Moon Size
Which world has the larger mean diameter?
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Your guess
Uranus
?mean diameter · kmmean diameter · twice JPL's mean radius
Make your call
Try Planet & Moon Size Blitz (60s)
Game snapshot: September 29, 2026 (UTC snapshot). Figures are rounded for display; comparisons use the underlying values. Source: NASA JPL Solar System Dynamics; twice the published mean radius
Learn while you play
Moons can challenge planets
- Ganymede and Mercury make a useful moon-versus-planet comparison.
- Titan and the Moon test whether familiarity matches physical size.
- Small irregular moons are compared by equivalent mean diameter, not their longest dimension.
Compare the size of Solar System worlds
Compare planets and moons by mean diameter in kilometres. Diameter is twice the mean radius published by NASA's Jet Propulsion Laboratory. Mass, surface gravity, distance from the Sun and the size of a ring system do not count.
All worlds use the same definition. Giant planets are flattened by rotation and some small moons are irregular; mean diameter provides a consistent equivalent size rather than mixing equatorial widths and longest axes.
NASA JPL physical parameters
The snapshot uses the Solar System Dynamics planetary and satellite physical-parameter tables. Each item links to the relevant source. Values are derived from published mean radii; labels show up to two decimal places and scoring retains the underlying precision. Equal displayed sizes are never paired.
Published radii have measurement uncertainties. Very close values should be read as comparisons of this source snapshot, not a claim that nature has been measured without error. Images are not shown to scale. Some small moons have only low-resolution spacecraft observations rather than detailed surface portraits.
Planet & Moon Size FAQ
Are you comparing radius or diameter?
Mean diameter. Every stored value is twice the source's mean radius, expressed in kilometres.
Do Saturn's rings count?
No. Only the body's mean diameter counts; ring systems are excluded.
Can a moon be larger than a planet?
Yes. For example, Ganymede has a greater mean diameter than Mercury, despite being a moon of Jupiter.
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