Complete Neptune & Moons Reference Chart: Shape, Rotation, Atmosphere & Temperature
Predicted mathematically by Urbain Le Verrier and John Couch Adams before Johann Galle spotted it through a telescope on September 23, 1846, Neptune is the densest of all the giant planets (1.638 g/cm³). When Voyager 2 swept 4,950 kilometers above Neptune's north pole in August 1989, it revealed a dynamic cobalt-blue world with high-altitude white methane-ice cirrus clouds casting shadows 50 km down onto the main cloud deck, five dusty rings, six new inner moons, and an active cryovolcanic landscape on giant Triton.
Galatea 42:43 Ring-Arc Resonance, Naiad–Thalassa 73:69 Dance & Triton Tidal Decay
1. Neptune's Oblateness f & 2.61× Internal Heat Flux Ratio (R_eq = 24,764 km, R_pol = 24,341 km):
f = (R_eq - R_pol) ÷ R_eq = 0.01708 (1.71% Oblate Flattening), E_emitted ÷ E_absorbed = 2.61 ± 0.28
2. Galatea 42:43 Corotation Inclination Resonance Confining the 4 Adams Ring Arcs (a_Adams = 62,932.5 km):
42 · n_Galatea = 43 · n_Adams_Ring - Ω_apside [Creates 86 Equilibrium Potential Wells of 4.18° Each!]
3. Triton Retrograde Tidal Deceleration & Roche Limit Destruction Countdown (i = 156.88°, a = 354,759 km):
da/dt < 0 (Retrograde tidal bulge lags Triton) ⇒ Triton enters Neptune's Roche Limit in ~1.4 to 3.6 Billion Years!
f = (R_eq - R_pol) ÷ R_eq = 0.01708 (1.71% Oblate Flattening), E_emitted ÷ E_absorbed = 2.61 ± 0.28
2. Galatea 42:43 Corotation Inclination Resonance Confining the 4 Adams Ring Arcs (a_Adams = 62,932.5 km):
42 · n_Galatea = 43 · n_Adams_Ring - Ω_apside [Creates 86 Equilibrium Potential Wells of 4.18° Each!]
3. Triton Retrograde Tidal Deceleration & Roche Limit Destruction Countdown (i = 156.88°, a = 354,759 km):
da/dt < 0 (Retrograde tidal bulge lags Triton) ⇒ Triton enters Neptune's Roche Limit in ~1.4 to 3.6 Billion Years!
| World | Dimensions / Mean Diameter | True Geometric Shape | Rotation / Orbital Period | Density (g/cm³) | Atmosphere / Exosphere | Surface / Plume / Cloud Temp |
|---|---|---|---|---|---|---|
| 0. Neptune | 49,528 km (Eq) × 48,682 km (Pol) | 1.71% Oblate Spheroid + 5 Rings | 16h 06m 36s (2,100 km/h Winds!) | 1.638 g/cm³ (Densest Giant!) | 80.0% H2, 19.0% He, 1.5% CH4 | -201°C (72 K) at 1-Bar |
| 1. Naiad (N III) | 96 × 60 × 52 km (60.4 km) | Elongated Triaxial Potato (73:69 Dance) | 7h 03m 58s (Faster than Neptune!) | ~0.80 g/cm³ (Porous Rubble) | Vacuum (Inclined 4.75° weaving orbit) | -222°C (51 K) |
| 2. Thalassa (N IV) | 108 × 100 × 52 km (81.4 km) | Flattened Discoid Ellipsoid! | 7h 29m 15s (Faster than Neptune!) | ~1.23 g/cm³ | Vacuum (Co-orbital partner to Naiad) | -222°C (51 K) |
| 3. Despina (N V) | 180 × 148 × 128 km (156 km) | Triaxial Ellipsoid (Le Verrier Shepherd) | 8h 01m 55s (Faster than Neptune!) | ~1.20 g/cm³ | Vacuum (Transits Neptune's blue disk) | -222°C (51 K) |
| 4. Galatea (N VI) | 204 × 184 × 144 km (174.8 km) | Triaxial Ellipsoid (Adams Ring Shepherd) | 10h 17m 23s (42:43 Arc Resonance!) | ~0.75 g/cm³ | Vacuum (Confines 4 Adams Ring Arcs) | -222°C (51 K) |
| 5. Larissa (N VII) | 216 × 204 × 168 km (194 km) | Heavily Cratered Triaxial Rubble Body | 13h 19m 00s (Synchronous Lock) | ~1.20 g/cm³ | Vacuum (Re-accreted after Triton capture) | -222°C (51 K) |
| 6. Hippocamp (N XIV) | 34.8 km (Smallest Inner Moon!) | Bright Water-Ice Spall Fragment of Proteus | 22h 48m 10s (Just Inside Proteus) | ~1.30 g/cm³ | Vacuum (Blasted off Proteus by Pharos!) | -222°C (51 K) |
| 7. Proteus (N VIII) | 440 × 416 × 404 km (420 km) | Largest Irregular Box-Polyhedron! | 1 Day 02h 56m (1.122 d Locked) | ~1.30 g/cm³ | Vacuum (250-km Pharos Impact Basin!) | -222°C (51 K) |
| 8. Triton (Neptune I) | 2,706.8 km (99.5% of Mass!) | Sphere + Pink N₂ Cap & 8km Geysers | 5.877 Days (Retrograde 156.9° ↺!) | 2.061 g/cm³ (Rock + Ocean) | 14 µbar N₂ + CH₄ + Cloud Deck | -235.2°C (-391°F / 38 K)! |
| 9. Nereid (Neptune II) | 357 ± 13 km (Chaotic Rotator) | Sub-Spherical Scattered-Rubble Moon | 11h 35m Spin (360d e=0.75 Orbit!) | ~1.50 g/cm³ | Vacuum (Swings 1.37M to 9.66M km!) | -220°C (53 K) |