Mars Fact Sheet

Mars/Earth Comparison

Bulk parameters

                                   Mars           Earth     Ratio (Mars/Earth)
Mass (1024 kg)                     0.6419          5.9736         0.107
Volume (1010 km3)                 16.318         108.321          0.151
Equatorial radius (km)	           3397           6378            0.533
Polar radius (km)                  3375           6356            0.531
Volumetric mean radius (km)        3390           6371            0.532
Core radius (km)                   1700           3485            0.488
Ellipticity                        0.0065          0.0034         1.912
Mean density (kg/m3)               3933           5520            0.713
Surface gravity (m/s2)             3.69            9.78           0.377
Escape velocity (km/s)             5.03           11.19           0.450
GM (x 106 km3/s2)                  0.04283         0.3986         0.107
Bond albedo                        0.16            0.385          0.416
Visual geometric albedo            0.150           0.367          0.409
Visual magnitude V(1,0)           -1.52           -3.86             -
Solar irradiance (W/m2)             595           1380            0.431
Black-body temperature (K)       216.6           247.3            0.875
Topographic range (km)               36             20            1.800
Moment of inertia (I/MR2)          0.366           0.3308         1.106
J2 (x 10-6)                     1960.45         1082.63           1.811 

Orbital parameters

                                   Mars           Earth     Ratio (Mars/Earth)
Semimajor axis (106 km)          227.9           149.6            1.524
Sidereal orbit period (days)     686.980         365.256          1.881
Tropical orbit period (days)     686.930         365.242          1.881
Perihelion (106 km)              206.6           147.1            1.404
Aphelion (106 km)                249.2           152.1            1.638
Synodic period (days)            779.94             -               -
Mean orbital velocity (km/s)      24.13           29.79           0.810
Orbit inclination (deg)            1.85            0.00             -
Orbit eccentricity                 0.0934          0.0167         5.593
Sidereal rotation period (hrs)    24.6229         23.9345         1.029
Obliquity to orbit (deg)          25.19           23.45           1.074

Mars Observational Parameters

Discoverer:      Unknown
Discovery Date:  Prehistoric

Apparent diameter from Earth
        Maximum (seconds of arc)   25.7
        Minimum (seconds of arc)    3.5
Distance from Earth
        Minimum (106 km)           54.5
        Maximum (106 km)          401.3
Apparent magnitude at opposition   -2.0      

Mars Mean Orbital Elements (J2000)

Semimajor axis (AU)                  1.52366231
Orbital eccentricity                 0.09341233
Orbital inclination (deg)            1.85061
Longitude of ascending node (deg)   49.57854
Longitude of perihelion (deg)      336.04084
Mean Longitude (deg)               355.45332

Martian Atmosphere

Surface Pressure:  ~6.1 mb (variable) [6.9 mb to 9 mb (Viking 1 Lander site)]
Surface Density: ~0.020 kg/m3
Scale height:  11.1 km
Average temperature:  ~210 K
Diurnal temperature range: 184 K to 242 K (Viking 1 Lander site)
Wind speeds:  2-7 m/s (summer), 5-10 m/s (fall), 17-30 m/s (dust storm) (Viking Lander sites)
Mean molecular weight: 43.34 g/mole
Atmospheric composition (by volume):
    Major      : Carbon Dioxide (CO2) - 95.32% ; Nitrogen (N2) - 2.7%
                 Argon (Ar) - 1.6%; Oxygen (O2) - 0.13%; Carbon Monoxide (CO) - 0.08%
    Minor (ppm): Water (H2O) - 210; Nitrogen Oxide (NO) - 100; Neon (Ne) - 2.5;
                 Hydrogen-Deuterium-Oxygen (HDO) - 0.85; Krypton (Kr) - 0.3;
		 Xenon (Xe) - 0.08

Satellites of Mars

                                    Phobos         Deimos
Mean distance from Mars (km)         9377          23436
Sidereal orbit period (days)        0.31891        1.26244
Orbital inclination (deg)            1.08           1.79
Orbital eccentricity                0.0151         0.00033
Major axis radius (km)                13              8
Minor axis radius (km)                 9              5
Mass (1015 kg)                       10.8            1.8
Mean density (kg/m3)                 1900           1750
Geometric albedo                      0.06           0.07
Visual magnitude V(1,0)             +11.8          +12.89  

NASA Official: J. H. King, joseph.h.king@gsfc.nasa.gov
Last Updated: 27 November 1998, DRW