C.M. Rodrigue, 2007Geography, CSULB

Mars: Basic Planetary Characteristics

Geography 494-01

S/07

Dr. Christine M. Rodrigue

C.M. Rodrigue, 2007Geography, 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, 2007Geography, CSULB

Mars in Space

Orbital Characteristics Mars’ and Earth’s eccentricity

Mars has one of the greatest eccentricities in the solar system at 0.0934 Earth is one of the more circular at 0.0167

C.M. Rodrigue, 2007Geography, 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, 2007Geography, 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 Solar irradiance at Mars is about 590 W/m22 versus 1,350 W/m22 at Earth (~44%)

C.M. Rodrigue, 2007Geography, CSULB

Mars in Space

Orbital Characteristics Mars’ and Earth’s distance

from the Sun Solar irradiance at Mars is

about 590 W/m22 versus 1,350 W/m22 at Earth (~44%)

C.M. Rodrigue, 2007Geography, CSULB

Mars in Space

Orbital Characteristics Mars’ and Earth’s distance

from the Sun Solar irradiance at Mars is

about 590 W/m22 versus 1,350 W/m22 at Earth (~44%)

Here, it would be like living on Earth at 54 N or S in March or September

C.M. Rodrigue, 2007Geography, 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, 2007Geography, 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, 2007Geography, CSULB

Mars: Data from Robotic Missions

Rotational characteristics Axial tilt or obliquity:

Mars: 2511’ 24” (25.19 ) from the vertical of the ecliptic

Earth: 2326’24” (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, 2007Geography, 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 km3 (Earth: 1,083,200,000,000

km3 Mass: 641.85 x 1018 metric tons (Earth: 5,973.70 x 1018

metric tons) Mean density: 3.94 g/cm3 (Earth: 5.52 g/cm3), where

water = 1.00 Equatorial surface gravity: 3.693 m/s2 (Earth: 9.766 m/s2)

or about 38% of Earth’s Escape velocity: 11.18 km/sec (Earth: 5.02 km/sec)

C.M. Rodrigue, 2007Geography, CSULB

Mars in Space

Size Mars’ and Earth’s relative

sizes compared