Surface Gravity of Neptune
| Value | 11.15 m/s² |
| Status | Measured: ± 0.02 m/s² (0.0018 relative) |
| Source | NASA NSSDC Planetary Fact Sheet, Neptune (surface gravity, eq., 1 bar) |
| Categories | Astronomicalsolar-systemplanets |
| microgal | 1,115,000,000 μGal |
| milligal | 1,115,000 mGal |
| millimeter per second squared | 11,150 mm/s² |
| centimeter per second squared | 1,115 cm/s² |
| gal | 1,115 Gal |
| inch per second squared | 438.97638 in/s² |
| kilometer per hour per second | 40.14 km/h/s |
| foot per second squared | 36.581365 ft/s² |
| mile per hour per second | 24.94184 mph/s |
| meter per second squared | 11.15 m/s² |
| standard gravity | 1.1369836 g |
Learning zone
Neptune is the second and last planet whose surface gravity exceeds Earth's — 11.15 m/s² at the one-bar equator, rotation excluded; include the 16.11-hour spin's centrifugal term and the effective figure is 11.00. Seventeen Earth masses in a body only four Earths across is the trick Uranus, at nearly the same size but 14.5 Earth masses, cannot quite match. A visitor floating at Neptune's cloud tops would weigh 14 per cent more than at home, in air of hydrogen and methane at 72 K.
The gravity field carried the discovery era's finest measurement: Voyager 2's tracking through this field, combined with the orbit of Triton, weighed Neptune precisely enough to dissolve a century-old phantom. The residuals in Uranus's motion that had launched searches for a "Planet X" — Lowell's obsession, incidentally netting Pluto — vanished once the corrected Neptune mass was fed back into the ephemerides in 1993. The perturber never existed; the mass had simply been wrong.