Escape Velocity of Neptune
| Value | 23,500 m/s |
| Status | Conventional / typical value |
| Source | NASA NSSDC Planetary Fact Sheet, Neptune (escape velocity) |
| Categories | Astronomicalsolar-systemplanets |
| millimeter per year | 741,603,600,000,000 mm/yr |
| millimeter per hour | 84,600,000,000 mm/h |
| foot per day | 6,661,417,300 ft/d |
| inch per hour | 3,330,708,700 in/h |
| meter per day | 2,030,400,000 m/d |
| millimeter per minute | 1,410,000,000 mm/min |
| meter per hour | 84,600,000 m/h |
| inch per minute | 55,511,811 in/min |
| millimeter per second | 23,500,000 mm/s |
| foot per minute | 4,625,984.3 ft/min |
| centimeter per second | 2,350,000 cm/s |
| meter per minute | 1,410,000 m/min |
| inch per second | 925,196.85 in/s |
| kilometer per hour | 84,600 km/h |
| foot per second | 77,099.738 ft/s |
| mile per hour | 52,568.003 mph |
| knot | 45,680.346 kn |
| meter per second | 23,500 m/s |
| mach (sea level) | 69.057932 Ma |
| kilometer per second | 23.5 km/s |
| speed of light | 0.000078387562 c |
Learning zone
Neptune's 23.5 km/s escape speed keeps every gas it ever collected, hydrogen included, at cloud-top temperatures of 72 K. But the more consequential escapes are the ones Neptune forbids other bodies: as the outermost giant it rules the Kuiper belt, ejecting or capturing whatever crosses it. Triton — the only large moon orbiting backwards — is almost certainly a captured Kuiper belt dwarf, a sibling of Pluto that came too close and lost; its retrograde orbit is slowly decaying, and in a few billion years Neptune's tides will tear it into a ring.
For spacecraft the number has been paid once. Voyager 2, closing its Grand Tour in 1989, skimmed 4950 km over Neptune's north pole — the closest any Voyager came to any planet — and used the encounter to bend down toward Triton, trading escape-speed margin for the last new world of the twentieth century.