Neptune
Mercury
Diameterkm
49,528
4,879
Mass (Earth = 1)x
17.15
0.06
Surface Gravitym/s²
11.15
3.70
Mean Temperature°C
-214
+167
Distance from SunAU
30.07
0.39
Orbital Perioddays
59,800
87.97
Day Lengthhours
16.11
4222.60
Known Moons
16
0
Axial Tilt°
28.32
0.03
Orbital Velocitykm/s
5.43
47.36
Quick Facts
Neptune
- -Neptune has the strongest winds in the solar system, reaching speeds of up to 2,100 km/h.
- -Neptune was the first planet discovered through mathematical prediction rather than observation.
- -One year on Neptune lasts about 165 Earth years -- it has completed just one orbit since its discovery in 1846.
- -Neptune's moon Triton orbits backward (retrograde), suggesting it was captured from the Kuiper Belt.
Mercury
- -Mercury's day-night cycle lasts 176 Earth days -- longer than its year of 88 Earth days.
- -A person weighing 68 kg on Earth would weigh only 25.7 kg on Mercury.
- -Mercury has ice in permanently shadowed craters near its poles despite surface temperatures reaching 430°C.
- -Mercury is shrinking -- its circumference has decreased by about 14 km as its core slowly cools and contracts.