Astronomy 171
Solar System Astronomy
Prof. Paul Martini

Lecture 34: Red Mars

Key Ideas:

Mars is the fourth planet from the Sun: About half the size of the Earth; Two moons: Phobos and Deimos
Atmosphere:: Thin, dry CO₂ atmosphere
Surface:: Cratered highlands and low-lying plains; Polar caps of CO₂ and water ice; Extinct volcanoes; Deep canyons and flow channels

Atmosphere of Mars

95% CO₂, 2.7% N₂, 1.6% Argon
Traces of H₂O (0.03%)
Only 0.007 times the pressure of Earth's atmosphere at sea level: Like being at an altitude of 30 km on Earth

Evolution of the Martian Atmosphere

Maybe warm enough for liquid water during the first Gyr: CO₂ got locked into carbonaceous rocks?
As Mars cooled:: H₂O froze out into the subsoil; Remaining CO₂ and N₂ escaped the low gravity of Mars
Left a thin, cold, and dry atmosphere of CO₂ and N₂

Weather on Mars

Temperatures:: Daytime: 244 K (-20 F) max; Nighttime: 187 K (-123 F) min
Surface winds:: 17 km/h (11 mph), up to 30 km/s (31 mph); Seasonal high winds can raise dust storms; Storms can cover the entire planet
High, thin clouds, fog, and frost

The Surface of Mars

Cratered Highlands: Old, heavily cratered surface dominated the southern hemisphere; Craters show signs of wind erosion; Crossed by deep valley networks; Smooth areas between creaters due to volcanism
Plains:: Dominate the northern hemisphere of Mars; Lightly cratered and thus younger; Tharsis plain may be only 500 Myr old

Polar Caps

North and South poles are capped by deposits of CO₂ and H₂O iceas mixed with dust: Shrink in the summer and grow in the winter

Olympus Mons

In Tharsis Plateau: Largest volcano in the Solar System; 24 km high; 600 km across
Stationary hotspot: One big shield volcano instead of a chain of smaller volcanoes; Last erupted about ~300 Myr ago

Canyons and Channels

Valles Marineris:: Vast canyon (rift valley) 4000 km long, 2-7 km deep, and up to 600 km wide; Formed by faulting (crust pulling apart), not by water erosion
Flow Channels: Deep channels and flood plains; Signs of sudden flows in the distant past (not steady-state flows like rivers on Earth)

Water on Mars?

Results from the Mars orbital surveys:: Evidence of recent, rapid floods of water carving gullies like seen on Earth; Layered terrains (e.g. like Grand Canyon)
Mars Exploration Rovers:: Layered sedimentary rocks with flow patterning; Salt deposits laid down by evaporating water; Hydrated minerals like Hematite

Life on Mars?

If there was liquid water in Mars' past, did that also mean life?: No evidence of present life from Viking landers; Strong evidence of standing water in the past
Possible life hiding deep underground?: Liquid water deep underneath the ground?; Would shield life from UV from the Sun

Strong motivation for future Mars exploration is to search for past or present life

See A Note about Graphics to learn why some of the graphics shown in the lectures are not reproduced with these notes.