Transcript Surface of Terrestrial Planets

Terrestrial Planet Surfaces
How do they compare to one another?
Lets Play “Guess Which Surface is
which?”
Mercury
The Moon
Hmm…Mars?
Venus
Home Sweet Home!
Comparison of Planetary Surfaces
• Mercury & the Moon
• heavily cratered {scars from the heavy bombardment}
• some volcanic plains
• Venus
• volcanoes and bizarre bulges
• Mars
• volcanoes and canyons
• apparently dry riverbeds {evidence for running water?}
• Earth
• all of the above plus liquid water and life
Geological Destiny
A planet’s fundamental properties determine its geological fate.
• Impact cratering
• important early on
• affects all planets equally
• Volcanism & Tectonics
• become dominant later on
• require internal heat
• size determines how long
a planet remains hot
• Erosion
planet size determines fate
• ultimately dominant
• requires volcanism for
outgassing of atmosphere
Inside the Terrestrial Worlds
• After they have formed, the molten planets
differentiate into three zones:
• core - made of metals
• mantle - made of dense rock
• crust - made of less dense rock
• Lithosphere - the rigid, outer layer of crust & part
of the mantle which does not deform easily
Inside the Terrestrial Worlds
Inside the Terrestrial Worlds
active geology
inactive geology
Image from:
http://www.washington.edu/burkemuseum/
geo_history_wa/
• Planetary
interiors heat up
through:
• accretion
• differentiation
• radioactivity
Supplies all the heat
at the beginning
Supplies heat throughout
the planet’s life
As mass “falls” inward, gravitational energy is
converted to random kinetic energy—this is the famous
“helmoltz mechanisim”
Cooling the Terrestrial Worlds
• Planets cool off through:
• conduction - heat flowing on the microscopic
level
• convection - heat flowing on the macroscopic
level (bulk motions)
• eruptions – a violent form of convection--hot
lava bursts through crust
• Cooling also occurs through radiation (but
much slower than the other mechanisms)
Cooling the Terrestrial Worlds
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Geometry of Cooling!
Heat escapes through surface area
Heat is retained by volume
Ratio of Area to volume
Determines rate of cooling –smaller
means faster cooling!
V=LxLxL
A=LxL
A/V = 1/L
Here L = 3 cm, so A/V = 1/3
What about a smaller cube, 1 cm on a
side?
A/V = 1/1 so it will cool three times
faster (or hot 1/3 as long)
Rate of cooling depends on Radius
Heat is contained with Volume
but passes out through surface
The ratio of Area to volume =
3/R
(Similar to Cube L -> R)
The smaller the Radius, the
more area there is compared
with volume
Mars has half the radius of Earth,
so it cools off twice as fast!
Impact Cratering
• objects hit planet at 10 – 70 km/s
• solid rock is vaporized
• a crater is excavated
• The diameter of crater is about ten times the
size of the impactor
• craters are circular
– large craters have a central peak
Counting Craters to find Surface Age
• Cratering rate decreased as Solar Systems aged.
• The older the surface, the more craters are present.
Tectonics
• convection cells in the
mantle causes both:
• compression in lithosphere
• mountains are produced
• extension in lithosphere
• valleys are produced
• mountains & valleys
appear on the surface
Erosion
• movement of rock by ice,
liquid, or gas
• valleys shaped by glaciers
• canyons carved by rivers
• sand blown by wind
• erosion not only wears
down features, it also
builds them:
• sand dunes
• river deltas
• sedimentary rock
Volcanism
• Underground, molten rock, called
magma, breaks through crack in
the lithosphere.
• Trapped gases are released:
• H2O, CO2, N2
• Viscosity of lava (typically basalt)
determines type of volcano
Volcanoes
Volcano Arenal—Costa Rican Stratovolcano
(image from: www.adventure-inn.com)
Shield Volcano
Mauna Kea on Hawaii…note moonrise through
shadow!
Shield Volcanoes can grow to great
size over hotspots
Hawaii—Mauna Loa and Mauna Kea—Kilauea
in Red
Atmosphere is formed from
outgassing
• This sounds subtle but
it isn’t!
Mars
• Olympus Mons
• the largest volcano in our
Solar System
• it is located atop the
Tharsis Bulge along with
several other volcanoes
Martian Atmosphere outgassed just like Earth’s
—primarily CO2 , H2O and SO2, and N2
Martian Pressure is 1/180 of Earth’s pressure..so where did all
the air go?
Volcanism on Venus
•Highest Volcano is Maxwell (17 km high)—plenty of
sources of outgassing
•Pancake Volcano are common
•Atmospheric pressure is 90 x earth’s pressure!
•Venus doesn’t have a true crust since its still in the
Oven!