mars: basic planetary characteristics
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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
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