Is Mars the same size as the Earth? What are the major differences between Earth and Mars? What are their similarities? The data below, courtesy of NSSDC, will help you determine the answer: You may also want to link to the Mars Today site.

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)             3394           6378            0.532
Polar radius (km)                  3372           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
Equatorial inclination (deg)      23.98           23.44           1.023

Martian Atmosphere

Surface Pressure:   6.9 mb to 9 mb (Viking Lander 1 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 Lander 1 site)
Wind speeds:  2-7 m/s (summer), 5-10 m/s (fall), 17-30 m/s (dust storm) (Viking Lander sites)
Atmospheric composition:  95.3% Carbon Dioxide, 2.7% Nitrogen, 1.6% Argon, 0.4% Other
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     

Notes on the factsheets - definitions of parameters, units, notes on sub- and superscripts, etc.

Mars Home Page

Directory to other Planetary Fact Sheets

NSSDC Planetary Home Page

NASA Official: J. H. King, king@nssdca.gsfc.nasa.gov
Last Updated: 14 February 1997, DRW