Mars Fact Sheet

Mars/Earth Comparison

Bulk parameters

	Mars	Earth	Ratio (Mars/Earth)
Mass (10²⁴ kg)	0.64169	5.9722	0.107
Volume (10¹⁰ km³)	16.312	108.321	0.151
Equatorial radius (km)	3396.2	6378.1	0.532
Polar radius (km)	3376.2	6356.8	0.531
Volumetric mean radius (km)	3389.5	6371.0	0.532
Core radius (km)	1830^**	3485	0.525
Ellipticity (Flattening)	0.00589	0.00335	1.76
Mean density (kg/m³)	3934	5513	0.714
Surface gravity (mean) (m/s²)	3.73	9.82	0.380
Surface acceleration (eq) (m/s²)	3.69	9.78	0.377
Surface acceleration (pole) (m/s²)	3.73	9.83	0.379
Escape velocity (km/s)	5.03	11.19	0.450
GM (x 10⁶ km³/s²)	0.042828	0.39860	0.107
Bond albedo	0.250	0.294	0.850
Geometric albedo	0.170	0.434	0.392
V-band magnitude V(1,0)	-1.60	-3.99	-
Solar irradiance (W/m²)	586.2	1361.0	0.431
Black-body temperature (K)	209.8	254.0	0.826
Topographic range (km)	30	20	1.500
Moment of inertia (I/MR²)	0.366	0.3308	1.106
J₂ (x 10^-6)	1960.45	1082.63	1.811
Number of natural satellites	2	1
Planetary ring system	No	No

^** Recent results indicate the radius of the core of Mars may only be 1650 - 1675 km.

Orbital parameters

	Mars	Earth	Ratio (Mars/Earth)
Semimajor axis (10⁶ km)	227.956	149.598	1.524
Sidereal orbit period (days)	686.980	365.256	1.881
Tropical orbit period^* (days)	686.972	365.242	1.881
Perihelion (10⁶ km)	206.650	147.095	1.405
Aphelion (10⁶ km)	249.261	152.100	1.639
Synodic period (days)	779.94	-	-
Mean orbital velocity (km/s)	24.08	29.78	0.809
Max. orbital velocity (km/s)	26.50	30.29	0.875
Min. orbital velocity (km/s)	21.97	29.29	0.750
Orbit inclination (deg)	1.848	0.000	-
Orbit eccentricity	0.0935	0.0167	5.599
Sidereal rotation period (hrs)	24.6229	23.9345	1.029
Length of day (hrs)	24.6597	24.0000	1.027
Obliquity to orbit (deg)	25.19	23.44	1.075
Inclination of equator (deg)	25.19	23.44	1.075

^* Mean value - the tropical orbit period for Mars can vary from this by up to 0.004 days depending on the initial point of the orbit.

Mars Observational Parameters

Discoverer:      Unknown
Discovery Date:  Prehistoric

Distance from Earth
        Minimum (10⁶ km)           54.6
        Maximum (10⁶ km)          401.4
Apparent diameter from Earth
        Maximum (seconds of arc)   25.6
        Minimum (seconds of arc)    3.5
Mean values at opposition from Earth
        Distance from Earth (10⁶ km)         78.34    
        Apparent diameter (seconds of arc)   17.8
        Apparent visual magnitude            -2.0
Maximum apparent visual magnitude            -2.94

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

North Pole of Rotation

Right Ascension: 317.681 - 0.106T
Declination    :  52.887 - 0.061T
Reference Date : 12:00 UT 1 Jan 2000 (JD 2451545.0)
T = Julian centuries from reference date

Martian Atmosphere


Surface pressure:  6.36 mb at mean radius (variable from 4.0 to 8.7 mb depending on season)  
                   [6.9 mb to 9 mb (Viking 1 Lander site)]
Surface density: ~0.020 kg/m³
Scale height:  11.1 km
Total mass of atmosphere: ~2.5 x 10¹⁶ kg
Average temperature:  ~210 K (-63 C)
Diurnal temperature range: 184 K to 242 K (-89 to -31 C) (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 
Atmospheric composition (by volume): 
    Major      : Carbon Dioxide (CO₂) - 95.1% ; Nitrogen (N₂) - 2.59%
                 Argon (Ar) - 1.94%; Oxygen (O₂) - 0.16%; Carbon Monoxide (CO) - 0.06% 
    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
Semimajor axis* (km)	9378	23459
Sidereal orbit period (days)	0.31891	1.26244
Sidereal rotation period (days)	0.31891	1.26244
Orbital inclination (deg)	1.08	1.79
Orbital eccentricity	0.0151	0.0005
Subplanetary axis radius (km)	13.0	7.8
Along-orbit axis radius (km)	11.4	6.0
Polar axis radius (km)	9.1	5.1
Mass (10¹⁵ kg)	10.6	2.4
Mean density (kg/m³)	1900	1750
Geometric albedo	0.07	0.08
Visual magnitude V(1,0)	+11.8	+12.89
Apparent visual magnitude (V₀)	11.3	12.40

*Mean orbital distance from the center of Mars.

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

Planetary Fact Table - metric units
Planetary Fact Table - U.S. units
Planetary Fact Table - Earth ratio

Mars Home Page

Directory to other Planetary Fact Sheets

Author/Curator:
Dr. David R. Williams, dave.williams@nasa.gov
NSSDCA, Mail Code 690.1
NASA Goddard Space Flight Center
Greenbelt, MD 20771
+1-301-286-1258