Hubble Space Telescope image made in February 1995.  It was spring in the northern hemisphere, so most of the carbon dioxide frost layer on the permanent water-ice cap had sublimated.  Near the western limb, volcano Ascraeus Mons towers 25 kilometers above the surrounding plains, poking through morning water-ice clouds which formed during the cold night.  Valles Marineris is southeast of it. A few percent iron oxide in the soil makes it red-orange.

Orbital Elements
Mean distance from Sun227,940,000 km    =    1.5237 astronomical units
Perihelion distance206,700,000 km=    1.3817 astronomical units
Aphelion distance249,100,000 km=    1.6651 astronomical units
Eccentricity of orbit0.0934
Inclination of orbit1.850relative to Earth's orbit
Period of orbit686.98 days=    686:23:31:12
Synodic period780 daysrelative to Earth
Mean orbital speed24.13 km/s
Minimum orbital speed21.97 km/s
Maximum orbital speed26.50 km/s
Physical Properties
Mean diameter6,780 km=    0.532  Earth diameter
Polar radius3,376 km
Equatorial radius3,397 km
Mass6.421 x 1023 kg=    0.10745 Earth mass
Mean density3.94 gm/cm3
Rotational period1.02595675 days=    24.622962 hours      =    24:37:22
Length of day1.0274907 days=    24.6597768 hours    =    24:39:35
Inclination of axis25.19relative to the axis of its orbit
Gravity at surface3.72 m/s2
Escape speed5 km/sfrom surface at equator
Visual geometric albedo0.15
Visual magnitude (Vo)-2.9maximum, as seen from Earth
Mean surface temperature    -63C
Maximum surface temperature    20C
Minimum surface temperature-140C
Atmospheric pressure0.007 barvaries with seasons by 25%
Atmosphere   composition by volume
Carbon dioxide (CO2)95.32%
Nitrogen (N2)2.7%
Argon (Ar)1.6%
Oxygen (O2)0.13%
Carbon monoxide (CO)0.07%
Water (H2O)0.03%
Neon (Ne)0.00025%
Krypton (Kr)0.00003%
Xenon (Xe)0.000008%
Ozone (O3)0.000003%

Two small moons:

HomeTo my Space and Science home page  for more about the Solar System

Jeff Root
September 4, 2003