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Transcript
Mars:
Basic Planetary Characteristics
Geography 494-01
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 semimajor 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 0.0934
 Earth is one of the more circular at 0.0167
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
 Solar irradiance at Mars is about 590 W/m2 versus 1,350 W/m2 at Earth (~44%)
C.M. Rodrigue, 2007
Geography, CSULB
Mars in Space
 Orbital Characteristics
 Mars’ and Earth’s distance
from the Sun
 Solar irradiance at Mars is
about 590 W/m2 versus
1,350 W/m2 at Earth
(~44%)
C.M. Rodrigue, 2007
Geography, CSULB
Mars in Space
 Orbital Characteristics
 Mars’ and Earth’s distance
from the Sun
 Solar irradiance at Mars is
about 590 W/m2 versus
1,350 W/m2 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 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, 2007
Geography, CSULB
Mars in Space
 Size
 Mars’ and Earth’s relative
sizes compared
C.M. Rodrigue, 2007
Geography, CSULB