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Mars Basic Data

Physical planetary properties

Mars is slightly more than half as large as Earth, and about double as large as the Earth's Moon in diameter. It is about 1.5 times more remote from the Sun so that it receives less than 1/2 the radiation as innermore planet Earth.

Here we give some bulk properties of planet Mars as compared to the Earth and Earth's Moon:

                                 Mars       Earth        Moon      Ratio      Ratio       Ratio
                                                                 Mars/Earth Moon/Earth  Moon/Mars
Mass (10^24 kg)                  0.64185     5.9736      0.07349   0.107      0.0123      0.114
Volume (10^10 km^3)             16.318     108.321       2.1958    0.151      0.0203      0.135
Equatorial radius (km)        3397        6378.1      1738.1       0.533      0.2725      0.512
Polar radius (km)             3375        6356.8      1736.0       0.531      0.2731      0.514
Volumetric mean radius (km)   3390        6371.0      1737.1       0.532      0.2727      0.512
Core radius (km)              1700        3485                     0.488    
Ellipticity (Flattening)         0.00648     0.00335     0.0012    1.93       0.36        0.19
Mean density (kg/m^3)         3933        5515        3350         0.713      0.607       0.852
Surface gravity (m/s^2)          3.71        9.80        1.62      0.379      0.165       0.437
Surface acceleration (m/s^2)     3.69        9.78        1.62      0.377      0.166       0.439
Escape velocity (km/s)           5.03       11.19        2.38      0.450      0.213       0.473
GM (x 10^6 km^3/s^2)             0.04283     0.3986      0.0049    0.107      0.0123      0.115
Bond albedo                      0.250       0.306       0.11      0.817      0.360       0.441
Visual geometric albedo          0.150       0.367       0.12      0.409      0.330       0.807
Visual magnitude V(1,0)         -1.52       -3.86       +0.21       -          -           -
Solar irradiance (W/m^2)       589.2      1367.6      1367.6       0.431      1.000       2.320
Black-body temperature (K)     210.1       254.3       274.5       0.826      1.079       1.307
Topographic range (km)          30          20          16         1.500      0.800       0.533
Moment of inertia (I/MR^2)       0.366       0.3308      0.394     1.106      1.191       1.077
J2 (x 10^-6)                  1960.45     1082.63      202.7       1.811      0.187       0.103
Number of natural satellites     2           1           0

Orbit

Mars orbits the Sun on an ecliptical orbit, which is considerably more excentric than the nearly-circular orbit of Earth, and larger (i.e. outside, or farther away from the Sun).

Astronomical parameters of Mars' orbit around the Sun (heliocentric coordinates):

Semimajor axis (a):                 1.52366231 AU = 227,936,670 km
Excentricity (e):                   0.09341233 + 0.000092 * T
Inclination w.r.t. ecliptic (i):    1.8496 deg - 0.0007 * T
Inclination w.r.t. ecliptic
  of 2000.0 (i0):                   1.8496 deg - 0.0083 * T
Length of Ascending Node (Omega):  49.577  deg + 0.771 * T
Length of Ascending Node in
  2000.0 coordinates (Omega0):     40.577  deg - 0.295 * T
Length of Perihelion (Lp):        336.0590 deg + 1.8408 * T
Length of Perihelion in
  2000.0 coordinates (Lp0):       336.0590 deg + 0.4438 * T
Length of planet Mars in J2000.0: 355.4469 deg

(where T is the number of centuries from epoch J2000.0). You can calculate Mars' approximate position on its orbit from these data.

Derived properties of Mars' orbit:

Perihelion:                         1.38133346 AU = 206,644,574 km
Aphelion:                           1.66599116 AU = 249,228,765 km

Orbit of Mars compared to Earth-Moon system:

                                 Mars     Earth/Moon    Ratio 
                                                      Mars/Earth  
Semimajor axis (10^6 km)       227.92      149.60        1.524
Sidereal orbit period (days)   686.980     365.256       1.881
Tropical orbit period (days)   686.973     365.242       1.881
Perihelion (10^6 km)           206.62      147.09        1.405       
Aphelion (10^6 km)             249.23      152.10        1.639
Synodic period (days)          779.94         -            -
Mean orbital velocity (km/s)    24.13       29.78        0.810 
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)          1.850       0.000         -
Orbit eccentricity               0.0935      0.0167      5.599
Sidereal rotation period (h)    24.6229     23.9345      1.029
Length of day (hrs)             24.6597     24.0000      1.027
Obliquity to orbit (deg)        25.19       23.45        1.074

Rotation

Like Earth and most other planets, Mars rotates, with a siderial period of 24h 37m 22.65s, only slightly more than Earth's 23h 56m 4.09s. Synodical rotation periods, or day lengths, are 24h 39m 35s and 24h 00m 00s (by definition), respectively. A Mars day is often referred to as "Sol" (Latin for Sun).

Mars' rotation is best characterized by the position of its poles in the celestial sphere, i.e., the orientation of its axis. The North Pole is situated at coordinates (J 2000.0):

     RA = 317.681 - 0.108 *  T ;   Dec = +52.886 - 0.061 * T

where T is the difference in centuries from 2000.0. Thus the poles are well lying within the band of the Milky Way, currently - as for Earth, the poles of Mars precess around its orbital poles (which are close to the Earth's North and South Ecliptic Pole, respectively).

View of the Martian North Celestial Pole (RA 21:10:43, Dec +52:53.2 (2000.0))
View of the Martian South Celestial Pole (RA 09:10:43, Dec -52:53.2 (2000.0))

The planet's equator is inclined by 25 deg 11' (25.19 deg) against the planet's orbital plane, with Mars' vernal equinox in a direction of about 85 deg heliocentric longitude (thus, this angle from Earth's vernal equinox). The planet experiences seasons similar to that of Earth, but due to its higher orbital excentricity, their length is quite different:

    Northern spring / southern fall:    199.6 (Earth) days
    Northern summer / southern winter:  181.7
    Northern fall   / southern spring:  145.6
    Northern winter / southern summer:  160.1

Like on Earth, the vernal equinox defines a Zero point for Mars' ecliptical coordinates. The Sun as seen from Mars is at longitude Ls (and latitude 0) in this coordinate system, which changes as Mars orbits the sun: It is at Ls = 0 when Northern spring begins, at Ls = 90 deg at Northern summer beginning, Ls = 180 deg at Northern vernal equinox, and Ls = 270 deg at Northern winter solstice.

Hartmut Frommert [contact]

Last Modification: August 31, 2003