Download Life in the Universe

Earth-like Planets
Part II
Lecture 21
Topography of Mars
 Northern lowlands and southern highlands (like our Moon : crustal dichotomy)
 Southern highlands (oldest region on the Mars)  several billions old
Topography of Venus
 Excepting for a few localized highlands, the surface of Venus is flat! Why?
 About 500 million years old or younger (few impact craters)
Tectonics in Venus
Flake Tectonics on Venus
Plate Tectonics
Flake Tectonics
Due to a very thin crust
Notable features on Mars
Valles Marineris
Volcanoes on Venus and Mars
These volcanoes are due to hot-spot volcanism (similar to the Hawaiian islands)
about 80% of the surface of Venus is
covered with lava flows
Olympus Mons : Largest Volcano in the Solar System
 Like Hawaiian volcanoes, it is a shield volcano
Comparison against tallest mountains
in Mars, Venus, and Earth.
Why the largest volcano on the smallest planet?
Tectonics make it harder to produce larger volcanoes
 Moving-crust above a
hot spot makes a series
of smaller volcanoes not
a single larger one.
 Lacking plate tectonics
on Mars allows a buildup of the largest volcano
over millions of years.
Atmospheres of Venus and Mars
 Venus : sulfuric acid rain evaporates before reaching the ground
 Mars : dry ice (CO2) snows.
Very thick atmo.
Very thin atmo.
Circulation pattern of Venus
 Because of slow rotation, Venus has a simple 2-cell convection pattern.
High altitude wind (i.e., Jet-stream of Earth)
 Surface wind : 5km/h
 high-altitude wind : 350km/h
 causing V-shape feature
Super-rotation of atmosphere
Seaons on Mars : Martian north pole
 Day (20C) and night (-140C) at equator  seasonal temperature changes at poles
 Seasonal changes of polar ice (CO2) cause planet-wide seasonal winds.
 e.g., in the northern hemisphere winter: CO2 wind from North to South
Seasons on Mars
Summer (Viking lander 1)
Viking lander 2
Atmospheres of Earth
 Earth
Atmospheres of Venus
Atmospheres of Mars
 Mars : no-recycle, locked up atmosphere in permafrost
Viking Landers
1979
Viking Lander 1 & 2 : 1979
• Two landers within two months
landed at nearly opposite sites across
the planet.
• And two orbiters…
• A thin coating of ice on the rocks and
soil…
Many images over several months…
No visible life. But, what about its habitability now
(and the past)?
Rovers on Mars
Pathfinder  Spirit/Opportunity 
MSL rover “Curiosity” (about a size of
a small car, max speed = 90m/hour) :
mobility (3-12 miles) for more diverse
collection of sample!!
Water on Mars?
 Sedimentary rocks
 and hematite (bluish small rocks in the picture)  requires water to form.
Water on Mars?
 Subsurface water based on data obtained by Mars Odyssey spacecraft.
Evidence of surface water flow?
Evidence of Water flow?
August 1999
September 2005
Pheonix Lander Highlights
 Lander dug up Martian soil
several ice blocks were exposed
which were sublimated over 3-4
days
“sol” = Martian day = 24 hrs 39min
Pheonix lander confirmed water ice
Short-term climate changes of Mars
After losing its atmosphere and H2O,
has the climate of Mars unchanged for
the past 2-3 Gyr?
No. The climate had changed with
period of hundreds of thousands
years!
Ice ages of Earth  due to the change
of obliquity. 22° - 25° : small range due
to the stabilizing effect of the large
Moon
Mars does not have a large moon.
Closer to Jupiter  a much wider
range of obliquity change, 0° - 80°
Larger obliquity  warm summer pole
 more CO2  stronger greenhouse
effect  warmer temperature.
Even with this, average T couldn’t maintain
surface liquid water, but high enough to have
liquid water just beneath the surface!
Martian Moons
• Heavily cratered, synchronously
rotating rocks very close to Mars
(about 1/400 of the distance b/w
Moon and Earth).
• Deimos is moving away from Mars
like our Moon around the Earth
• Because Phobos is orbiting faster (7
hr 39 min) than Mars’ rotation,
Phobos is spiraling toward the Mars.
It will smash into the Mars in 40
million years.
They are likely captured asteroids.
In summary…
Important Concepts
Important Terms
 Flake tectonics
 Runaway greenhouse effect
 Runaway icehouse effect
 Reasons for Mars’ short-term
climate change
 Atmospheres of Venus and Mars
 No magnetic field on Venus &
Mars
 Martian moons
 Icehouse effect
 Flake tectonics
 Shield volcano
 Hot-spot volcanism
Chapter/sections covered in this lecture : sections 11-5 through 11-8