A3. Planetary Orbits & Figures
Sun = ☉ | Earth = ⊕ | Moon = ☾ | Mars = 🜔
Parameter | Mars | Earth | Mars/Earth |
Semi-major axis (10^6 km) | 227.939 | 149.60 | 1.524 |
Perihelion (10^6 km) | 206.62 | 147.09 | 1.405 |
Aphelion (10^6 km) | 249.23 | 152.10 | 1.639 |
Mean orbital velocity (km/s) | 24.07 | 29.78 | 0.808 |
Max. orbital velocity (km/s) | 26.50 | 30.29 | 0.875 |
Min. orbital velocity (km/s) | 21.97 | 29.29 | 0.750 |
Orbit inclination to ecliptic (°) | 1.850 | 0 | — |
Orbit eccentricity | 0.0935 | 0.0167 | 5.599 |
Sidereal rotation period (hr) | 24.6229 | 23.9345 | 1.029 |
Length of local day (hr) | 24.6597 | 24.0 | 1.027 |
Sidereal orbit period (days) | 686.980 | 365.256 | 1.881 |
Local days/year | 668.599 | 365.256 | 1.830 |
Obliquity of equator to orbit (°) | 25.19 | 23.439 | 1.075 |
Mass (10^24 kg) | 0.64171 | 5.9724 | 0.107 |
Volume (10^10 km^3) | 16.318 | 108.321 | 0.151 |
Equatorial radius (km) | 3,396.2 | 6,378.1 | 0.532 |
Polar radius (km) | 3,376.2 | 6,356.8 | 0.531 |
Volumetric mean radius (km) | 3,389.5 | 6,371.0 | 0.532 |
Core radius (km) | 1,700 | 3,485 | 0.488 |
Flattening | 0.00589 | 0.00335 | 1.76 |
Surface area (10^6 km^2) | 144.798 | 510.072 | 0.284 |
Dry surface area (10^6 km^2) | 144.798 | 149.062 | 0.971 |
Mean density (kg/m^3) | 3,933 | 5,514 | 0.713 |
Surface gravity (m/s^2) | 3.711 | 9.807 | 0.378 |
Escape velocity (km/s) | 5.027 | 11.186 | 0.450 |
Solar irradiance (W/m^2) | 586.2 | 1,361 | 0.431 |
Topographic range (km) | 30 | 20 | 1.5 |
Surface pressure (kPa)* | 0.636 | 101.325 | 0.006 |
Orbital characteristics
Semimajor axis (average Sun distance):
Earth: 149.598 × 10⁶ km (1.000 AU)
Mars: 227.956 × 10⁶ km (1.524 AU)
Orbital period (sidereal / tropical):
Earth: 365.256 d / 365.242 d
Mars: 686.980 d / 686.972 d
Eccentricity (how elliptical the orbit is):
Earth: 0.0167
Mars: 0.0935 (more elongated than Earth)
Inclination to ecliptic (J2000):
Earth: 0° (by definition of the ecliptic)
Mars: 1.848°
Perihelion / aphelion distance:
Earth: 147.095 × 10⁶ km / 152.100 × 10⁶ km
Mars: 206.650 × 10⁶ km / 249.261 × 10⁶ km
Mean orbital speed (min–max):
Earth: 29.78 km/s (29.29–30.29)
Mars: 24.08 km/s (21.97–26.50).
Synodic period (relative to Earth):
Earth: n/a
Mars: 779.94 d (interval between oppositions)
Rotation and seasons
Sidereal rotation period (spin relative to stars):
Earth: 23.9345 h
Mars: 24.6229 h
Solar day (“length of day”):
Earth: 24.0000 h
Mars: 24.6597 h (a sol ≈ 24 h 39 m 35 s)
Axial tilt (obliquity) / equator inclination:
Earth: 23.44°
Mars: 25.19° (broadly Earth-like seasons, but longer)
Seasonal asymmetry (by orbital dynamics):
Earth’s seasons are near-symmetric; Mars’s are asymmetric because of its higher eccentricity (southern summer is shorter/warmer; northern summer longer/cooler)
Size and shape (figure)
Equatorial radius / polar radius:
Earth: 6,378.137 km / 6,356.752 km
Mars: 3,396.2 km / 3,376.2 km
Mean (volumetric) radius
Earth: 6,371.000 km
Mars: 3,389.5 km
Flattening (ellipticity):
Earth: 0.003353
Mars: 0.00589 (slightly more oblate than Earth)
Topographic range (approx. peak-to-trough):
Earth: ~20.4 km
Mars: ~30 km (e.g., Olympus Mons to deep basins)
Mass, density, gravity, escape
Mass:
Earth: 5.9722 × 10²⁴ kg
Mars: 0.64169 × 10²⁴ kg
Mean density:
Earth: 5,513 kg/m³
Mars: 3,934 kg/m³
Surface gravity (mean):
Earth: 9.820 m/s²
Mars: 3.73 m/s² (~38% of Earth)
Escape velocity:
Earth: 11.186 km/s
Mars: 5.03 km/s