Earth
Mercury
Diameterkm
12,742
4,879
Mass (Earth = 1)x
1.00
0.06
Surface Gravitym/s²
9.81
3.70
Mean Temperature°C
+15
+167
Distance from SunAU
1.00
0.39
Orbital Perioddays
365.25
87.97
Day Lengthhours
24.00
4222.60
Known Moons
1
0
Axial Tilt°
23.44
0.03
Orbital Velocitykm/s
29.78
47.36
Quick Facts
Earth
- -Earth is the only planet not named after a Greek or Roman deity.
- -Earth's rotation is gradually slowing -- days are getting about 1.4 milliseconds longer per century.
- -About 71% of Earth's surface is covered by water, but 96.5% of that water is in the oceans.
- -Earth's magnetic field has flipped its polarity hundreds of times over millions of years.
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.