C.M. Rodrigue, 2007 Geography, CSULB Mars: Basic Planetary Characteristics Geography S/07 Dr. Christine M. Rodrigue

C.M. Rodrigue, 2007 Geography, CSULB Mars in Space  Orbital Characteristics  Planetary orbits are elliptical  The major focus of Mars' or Earth's orbit is inside the Sun  The plane of that orbit is the ecliptic  The diameter of the orbit along its long axis is the major axis  Half that distance is the semi- major axis (here shown as a)  The diameter of the planet's orbit along its short axis is the minor axis  Half that is the semi-minor axis  C on this graph is the distance from the center of the orbit to one focus  Eccentricity is c/a – 0 for a perfect circle

C.M. Rodrigue, 2007 Geography, CSULB Mars in Space  Orbital Characteristics  Mars’ and Earth’s eccentricity  Mars has one of the greatest eccentricities in the solar system at  Earth is one of the more circular at

C.M. Rodrigue, 2007 Geography, CSULB Mars in Space  Orbital Characteristics  Mars’ solar irradiance and surface insolation averaged over the year  Very freaky: South polar regions get the most solar radiation due to greater axial tilt, greater eccentricity, and the greater length of day  The length of day overcompensates for the lower sun angle  GEOG 442 students can compare with Lab 1

C.M. Rodrigue, 2007 Geography, CSULB Mars in Space  Orbital Characteristics  Mars’ and Earth’s distance from the Sun  Mars is about 227,936,640 km from the Sun averaged along the semi-major axis  Earth is 149,597,890 km 22  Solar irradiance at Mars is about 590 W/m 2 versus 1,350 W/m 2 at Earth (~44%)

C.M. Rodrigue, 2007 Geography, CSULB Mars in Space  Orbital Characteristics  Mars’ and Earth’s distance from the Sun 2 2  Solar irradiance at Mars is about 590 W/m 2 versus 1,350 W/m 2 at Earth (~44%)

C.M. Rodrigue, 2007 Geography, CSULB Mars in Space  Orbital Characteristics  Mars’ and Earth’s distance from the Sun 2 2  Solar irradiance at Mars is about 590 W/m 2 versus 1,350 W/m 2 at Earth (~44%)  Here, it would be like living on Earth at 54  N or S in March or September

C.M. Rodrigue, 2007 Geography, CSULB Mars in Space  Orbital Characteristics  Mars’ and Earth’s distance from the Sun  Mars at perihelion is 206,600,000 km (Southern Hemisphere summer)  Earth is 147,100,000 km (also Southern Hemisphere summer)  Mars at aphelion is 249,200,000 km  Earth is 152,100,000 km  So, Mars perihelion distance is only 82.9% of its aphelion distance  On Earth, perihelion is 96.7% of aphelion  On Earth, this difference is a trivial influence, especially since perihelion hits during the more oceanic hemisphere’s summer  On Mars, it’s a major seasonal driver

C.M. Rodrigue, 2007 Geography, CSULB Mars in Space  Orbital Characteristics  Mars’ and Earth’s changes in eccentricity  Planets’ orbital shapes alternate between more circular and more elliptical  Earth’s varies from ~0.01 to ~0.05 over a cycle of ~100,000 years  Mars’ varies from close to 0.00 to ~0.14

C.M. Rodrigue, 2007 Geography, CSULB Mars: Data from Robotic Missions  Rotational characteristics  Axial tilt or obliquity:  Mars: 25  11’ 24” (25.19  ) from the vertical of the ecliptic  Earth: 23  26’24” (23.44  ) from the vertical of the ecliptic  Mars’ axis precesses 360  in 93,000 Martian years or ~125,000 Earth years  Earth’s axis precesses 1  per 71.6 years or 360  in 25,765 years

C.M. Rodrigue, 2007 Geography, CSULB Mars: Data from Robotic Missions  Size  Mars and Earth compared:  Mars’ equatorial radius: 3,397 km (Earth: 6,378 km)  Equatorial circumference: 21,344 km (Earth: 40,075 km)  Volume: 163,140,000,000 km 3 (Earth: 1,083,200,000,000 km 3  Mass: x metric tons (Earth: 5, x metric tons)  Mean density: 3.94 g/cm 3 (Earth: 5.52 g/cm 3 ), where water = 1.00  Equatorial surface gravity: m/s 2 (Earth: m/s 2 ) or about 38% of Earth’s  Escape velocity: km/sec (Earth: 5.02 km/sec)

C.M. Rodrigue, 2007 Geography, CSULB Mars in Space  Size  Mars’ and Earth’s relative sizes compared