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Astronomy 311
Professor Lee Carkner
Lecture 14
Mars -- The God of War
The Canals of Mars
In 1877 G. Schiaparelli thought that he saw
intersecting straight lines on Mars
Percival Lowell built an observatory near
Flagstaff, AZ and published elaborate maps
of a network of canals and oasis on Mars
Mars Facts
Size: ~1/2 Earth size
Orbit: 1.5 AU
Celestial Motions of Mars
Mars rotates on its axis with a period of
24 1/2 hours
Mars has an orbital period of 23 months
Mars is tilted on its axis
Spacecraft to Mars
Mariner 4 was the first spacecraft to visit
Mars in 1964
Recent missions:
Mars Express (2003, orbiter)
Mars Reconnaissance Orbiter (2006, orbiter)
Spirit and Opportunity (2003, rover)
Surface Features
Volcanoes -- Mars has many shield volcanoes,
but they are not active today
Canyons -- Mars shows deep canyons, the
result of volcanic activity stressing the crust
Craters --The northern hemisphere is less
heavily cratered than the southern
Dust storms alter the Martian craters
Tharsis Rise
Olympus Mons
Valles Marineris
Cratering on Mars
Mars Topological Map
The Surface of Mars
Mars is red due to iron oxide (rust) in the soil
Surface is covered with reddish soil and is rocky
and broken
Mars is cold
Mars has seasons due to the tilt of its axis
Standing on Mars
Mars’s Atmosphere
Composition: 95% CO2, 3% N2, trace
amounts of water vapor and oxygen
Pressure: 0.007 atmospheres
Early Mars may have had a thicker CO2
and H2O atmosphere
Water on Mars
Mars is now a very dry world
Water ice may be present in the polar
ice caps (along with frozen CO2)
It is possible that water exists
Frost on Mars
Polar Ice Cap
Was Mars Wet?
 Surface features indicate that water once flowed freely on the Martian
 Due to:
 Global water (Many oceans, rivers, etc)?
 Mars may have been warmer with a thicker atmosphere in the past
 Where is the water now?
 Mars may warm up periodically allowing water to form (Mars may now be
in an ice age)
Dried-up River Bed
Past Water Erosion on Mars
Life on Mars?
 Mars shows evidence for liquid water and higher
temperatures in the past
 Viking tested soil samples but the results were inconclusive
 We do have a few meteors that were blasted off the surface
of Mars
 AH84001 shows some features that look a little like the remains of
life-forms, but evidence is not very strong
Viking’s Soil Scoop
Fossil Life in Martian
Cydonia “Face” on Mars
Traits of Psuedoscience
Avoidance of Occam’s Razor
Mars’s Interior
Mars has a lower density than the other terrestrial
planets (4000 compared to 5000 kg/m3)
No evidence for plate tectonics
We have very little other data on Mars’s interior
Continuing Mars Exploration
Phoenix, a small “scout” lander
mission, to be launched 2007
Sample return?
Manned mission?
A Possible History of Mars
Mars forms
Volcanism creates
volcanoes and lava
Mars losses internal
heat, crust cools
Atmosphere loses
CO2, atmosphere
Water freezes
Red, dusty, thin atmosphere
Mars is a medium-sized world
allowing it to retain an atmosphere
(unlike Mercury and the Moon), but not
a thick atmosphere (like Venus and
Mars shows signs of being habitable in
the past, but no good evidence of life
has been found
Summary: Surface
Mars has a red surface composed of
dust, soil and rocks
Mars has large volcanoes and deep
Dust storms often cover the surface
Mars has a low density and may not
have an iron core
Summary: Climate
Mars has a very thin atmosphere and is cold
Low temperature and pressure prevent
liquid water on the surface
Mars must have had a thicker, warmer
atmosphere in the past since there is
substantial evidence for water flows
Early thicker CO2 greenhouse atmosphere
gradually washed out by rainfall
The temperature on Mars may change over time
due to orbital variations