Body diameters to scale. Positions and surface artwork are illustrative; Saturn’s rings are excluded.
A change of perspective
8.3445× the diameter. See how the two worlds measure up.
Diameter is a distance across an object. Volume grows with the cube of that distance.
Choose a size to bring this comparison down to Earth.
Rhea: Calculated as twice JPL’s volume-equivalent mean radius of 763.50 ± 0.60 km: diameter = 1,527.0 ± 1.2 km. This describes a sphere with Rhea’s volume, rather than an equatorial or polar diameter. The adopted value has measurement uncertainty and is not exact.
Earth: Twice the source mean radius; body diameter only, excluding rings.
Calculated as twice JPL’s volume-equivalent mean radius of 763.50 ± 0.60 km: diameter = 1,527.0 ± 1.2 km. This describes a sphere with Rhea’s volume, rather than an equatorial or polar diameter. The adopted value has measurement uncertainty and is not exact.
Rhea’s adopted mean diameter is 1,527 km, calculated by doubling its mean radius. JPL defines that radius using a sphere with the same volume as the satellite, so the result is a volume-equivalent diameter. Equatorial and polar diameters describe specific directions instead. The radius uncertainty doubles too, giving ±1.2 km for diameter. Source: JPL Planetary Satellite Physical Parameters.
The artwork is illustrative; it is not a measured surface map.
Using JPL’s mean radii, Earth’s Moon has a diameter of 3,474.8 km. Dividing 1,527 by 3,474.8 gives approximately 0.439, so Rhea is about 44% as wide. If the Moon were a 10 cm ball, Rhea would be about 4.4 cm across. These are calculated, rounded length comparisons, not mass or volume ratios. Source values: JPL.
Rhea is Saturn’s second-largest moon, after Titan. Its heavily cratered surface makes it a useful example of an icy moon at a smaller scale than Earth’s Moon. Source: NASA’s Rhea overview.