Descriptive Astronomy 101

Mars - "The Red Planet"

Fourth planet from the Sun
- 227.9 million km
Revolution = 687 days
Rotation = 24hr 37min.
Diameter = 6,794 km (4,194 mi.)
density = 3.9 g/cm3
Axial Tilt = 25°
Mass = 6.42 x 1023 kg
Escape velocity = 5000 m/sec
Average distance from Sun = 1.524 AU
Rotation period (length of day) = 1.026 days
Revolution period (length of year) = 686.98 days
Orbit inclination = 1.85°
Orbit eccentricity = 0.093
Maximum surface temperature = 240 K
Minimum surface temperature = 190 K
Visual geometric albedo = 0.15
Highest point on surface = Olympus Mons
- (about 24 km above surrounding lava plains)
Atmospheric components - 95% CO2, 3% N2, 1.6% Ar

Early Observations

Red color is distinctive.
Dark patches on surface that changed seasonally
Polar ice caps that changed seasonally


Giovanni Schiaparelli, 1877 - "canali"
Percival Lowell, 1890


Differentiated core, mantle, crust
Core, 9-15% of planetary volume
Weak magnetic field suggesting solid core
Atmospheric components:

Crust Composition

Basaltic rock and altered materials
pyroxenite and diabase (ultramafic to mafic)

SNC Meteorites

Samples have been found on Earth - SNC meteorites
Shergotty, India
Nakhla, Egypt
Chassigny, France
Only 34 known samples from Mars
Dunite, pyroxenite, peridotite, diabase

Meteorite samples from Mars.
How is this possible?
How do we know that they are from Mars?

Tectonic Activity

No Earth-like plate tectonics
Plate tectonics did not develop. Why?


Major force in shaping the surface of Mars
Largest volcanoes in the Solar System
Olympus Mons is the largest (shield volcano)
Shield Volcanoes
Dome Volcanoes

Reason for large volcanoes is related to lack of plate tectonics on Mars.
Smaller diameter means more rapid planetary cooling.
- results in thick crust
- relatively immobile crust
Mantle plumes supply magma to single area over long periods of time.

Impact Craters

Impact Craters are prevalent
Similar morphology to lunar craters
Ejecta material show a lobate form
Modified by erosion since formation


Stream channels and drainage patterns, and gullies.

Eolian features

Dust storms:
Sand dunes:
Mass wasting:
Wind Streaks

Mass Wasting

The downhill movement of material under the influence of gravity
Slump - large blocks of material sliding or rotating downhill

Views from the surface

Viking lander view of surface 1
Viking lander view of surface 2
Pathfinder lander view of the surface 1
Pathfinder lander view of the surface 2
Mars Exploration Rover Mission - Spirit and Opportunity Rovers

Life on Mars?

Did life exist on Mars in the past?
Could life exist on Mars today?


Check the following site for more information and images on Mars
Mars Global Surveyor