Mercury
Mars
Diameterkm
4,879
6,779
Mass (Earth = 1)x
0.06
0.11
Surface Gravitym/s²
3.70
3.72
Mean Temperature°C
+167
-65
Distance from SunAU
0.39
1.52
Orbital Perioddays
87.97
687
Day Lengthhours
4222.60
24.66
Known Moons
0
2
Axial Tilt°
0.03
25.19
Orbital Velocitykm/s
47.36
24.07
Quick Facts
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.
Mars
- -Olympus Mons on Mars is about 21.9 km tall -- nearly three times the height of Mount Everest.
- -A Martian day (sol) is 24 hours and 37 minutes, remarkably similar to an Earth day.
- -Mars has seasons like Earth because its axial tilt (25.19°) is very similar to Earth's (23.44°).
- -Dust storms on Mars can grow large enough to engulf the entire planet and last for months.