Download Terrestrial Planets Notes

Terrestrial Planets
General Information
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Mercury diameter = 4880 km, no atmosphere
Venus diameter = _______ km, atmosphere
Earth diameter = 12800 km, atmosphere
Mars diameter = _________ km, atmosphere
Size and the distance from the Sun are
responsible for the differences in the
atmospheres on each planet.
Lore behind Mercury
• Named after the Messenger of the gods.
• It orbits around the Sun quickly.
• Moves across the sky quickly.
Mercury
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The smallest terrestrial planet
Similar in size and mass to our moon.
Has a mass of 1/20th of the Earth.
Mercury lacks an atmosphere
Earlier we discussed the importance of Surface
gravity and the presence of an atmosphere.
• Does anyone notice a discrepancy regarding
terrestrial planets, size, and the presence of an
atmosphere?
What is the deal with Mars?
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Mercury is small, Mars is less than 2,000 km larger.
Mercury has no atmosphere – Mars does!
Mars is half as big as Earth and its mass is 1/10th
Why does it have an atmosphere and not Mercury?
– There is no significant difference in surface gravity
(mercury = 0.38 mars = 0.380 of Earth)
– And they differ in mass by only .02
– Mercury escape velocity = 4.25 km/sec.
– Mars escape velocity = 5.03 km/sec
– Earth escape velocity = 11.3 km/sec
The answer lies in the distance
from the Sun and Temperature
• Mercury is VERY close to the Sun.
– Its equatorial temperatures during the day reach 700 K (that is
800 F).
– At night Temperatures drop dramatically to100 K (-280 F).
– The temperature is so great that the molecules are moving so
fast that they are able to escape into space.
• In addition, because of the dramatic changes in
temperature, IF any gas molecules were present, they
would be forced to the poles and then frozen into ice.
• Finally, Mercury shows little evidence of volcanic activity,
which is thought to be necessary for an atmosphere to
develop.
Mars on the other hand
• Mars has volcanoes, which act as a
source for gas.
• Mars is farther from the Sun so the gases
are not as hot and as a result do not move
around as much.
– The gas does not reach escape velocity.
• Temperature variations are not as great so
there is less movement of gas molecules.
Mercury
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Hypothesized to have a silicate mantle
A large iron-nickel core
It is unknown if the core is liquid
Mercury rotates very slowly
The rotation could have been slowed by a
collision with a large planetesimal. Fig 8.8
• The slow rotation in combination with lack of
movement of the core means a very weak
magnetic field.
• The Earth’s magnetic field manifests itself with a
compass.
Resonance and a Mercury Day
• Mercury rotates so slowly that it spins three
times for every 2 trips around the Sun.
• Because of tidal forces from the Sun
Mercury’s orbital speeds change.
• Mercury’s orbit is elliptical and is closer to the
sun at specific times.
• This results in
– When a force
that is repeatedly applied causes an increase
in motion.
Odd Fact
• Because of Mercury’s odd rotation
• A solar day is 176 Earth Days.
• The Sun changes its direction of motion in
the sky.
• It will set and then reverse and then set
again. See fig 8.9
Venus
• Most similar to the Earth in ________ and _____
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• Said to be Earth’s twin because of its size and
proximity to Earth
• However, its surface and atmosphere are very
different.
• The surface is covered with ____________.
The atmosphere of Venus
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96% ________ _________!
3.5% Nitrogen
The rest is a mix of water and other gases.
The clouds are composed of Sulfuric Acid.
The Sulfur compounds may have been ejected
from volcanoes and combined with some of the
water in the atmosphere to form the acid.
• Major Greenhouse effect.
• What is the Greenhouse effect?
Venus is easy to see
• The clouds reflect large amounts of
Sunlight
• As a result it is a large bright object in the
sky.
• You do not even need a telescope to see
it.
Venus and Temperature
• It is about 750 K – 900 F
• The temperature is a result of greenhouse
effect.
• The atmosphere ranges from the surface to
over 40 km up and continues to about 140km
• The atmospheric temperature drops because
the concentration of CO2 drops at higher
altitudes. At 40 km up the temperature is near
room temperature (300 K)
Venus topography
• No oceans
• Just lowlands and highlands
• The Highlands are mountainous and
similar to the continents. There are only 2
on Venus.
• Venus is volcanically active
• Some of the differences between the Earth
and Venus can be explained by the
amount of water molecules in the rock.
Water and rocks
• The amount of water in rock affects how
the rock melts during volcanic activity.
• It also affects how the rock and lava retain
heat.
• The more heat the rock retains the more
volcanic activity and shifts in the crust are
possible.
Rotation of Venus
• Venus spins very slowly and in the
opposite direction of other planets.
• Because it spins backwards it is said to
have retrograde rotation.
• As a result, the Sun rises in the west and
sets in the East.
• It takes 243 days to make one rotation.
• Its slow rotation results in no magnetism.
Two hypotheses regarding
retrograde rotation.
• A large planetesimal crashed into Venus
when it was first formed.
• This slowed the rotation and tilted its axis
• A second theory is that tidal effects from
the Sun and Earth altered the tilt angle.
• By changing the tilt angle, the rotation of
the planet was reversed and slowed.
Mars
• The planet that has gotten more attention than any
other except Earth.
• Named after the Roman god of __________.
• Appears almost blood red (hence the name).
• Temperature rarely gets _________________.
• Surface gravity is much less if you weigh 100 lbs. on
earth, you would weigh _______ lbs on mars
• Mars has ____ moons. ________ the largest,
_________, the smaller of the two.
• The Martian surface has some similarities to Earth’s.
Mars has been extensively studied
• Here are a few of the probes sent to take a
peek at Mars:
– Mariners
– Vikings
– Mars Global Surveyor
– Pathfinder
– Sojourner
– Mars Rovers (2) Spirit and Opportunity
Martian atmosphere
• Mostly CO2
• Small amounts of – N, Ar, O, CO, Ne, Kr,
Xe, H2O
• Atmospheric clouds – made of pink dust,
blue clouds of ice crystals, white clouds of
water vapor.
• The Earth’s atmosphere is mostly N.
Clouds on Earth are mostly clouds of water
vapor.
No Greenhouse Effect on Mars
• The density of CO2 and other gases in the
Martian atmosphere is very low. That means
there is not a lot of gas to start with.
• Even though the atmosphere is 95% CO2,
there is not enough to cause a greenhouse
effect. Thus Mars is still relatively cold.
• Think of it this way which is greater 95% of 5
or (percentage of CO2 in Earth atm.) .05% of
500
• Ans. = 95% of 5 = 4.75, .05% 0f 500 = 25.
Martian atmosphere (cont.)
• No rain because there is not enough water in the
atmosphere to form precipitation.
• There may be some frost and fog that condenses
into ice.
• There is frozen water at the poles and potentially
underground.
• It is believed that Mars may have had liquid water
a few billion years ago.
• There are two theories which explain why there is
no more liquid water on Mars.
How Mars lost its water
• The atmosphere is not dense enough to keep water
in liquid form and on the surface. (evaporates without
heat. Mars has a surface that has been freeze
dried!)
• Hypothesis 1: Mars had a dense atmosphere that
kept liquid water present, but an asteroid struck the
planet with such great force that some of the
atmosphere was knocked off because of the weak
surface gravity.
• Without the atmosphere, the liquid water was lost.
• The Earth may have had a similar collision that lead
to the demise of the dinosaurs.
How Mars lost its water
• Hypothesis 2 – The low surface gravity
allowed the gases to gradually escape.
Thus the atmosphere became less and
less dense.
• Volcanic activity slowed so less gas was
released to replace the gases that were
lost to space.
Martian surface
• The Martian surface shows little evidence
of erosion.
• It is dusty, rocky, and dry.
• Most of the dust is limonite, a red brick
colored mineral that is found in some
deserts on earth.
• Composed of silicates and iron.
Martian surface features
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Mars is similar to Earth in many aspects:
Immense canyons
Old lava flows
Ice caps which change in size due to seasonal
changes.
Martian Surface
• No indication of recent volcanic activity.
• The core of Mars is most likely solid and not
molten.
• No tectonic activity.
• Ice caps on poles made of dry ice (frozen CO2)
and frozen water.
– The Southern cap is dry ice
– The Northern cap has a thin layer of dry ice with a
thicker layer of frozen water underneath.
Martian poles
• The size of the polar caps changes with season.
• Because of the tilt of the planet (similar to Earth)
Mars has seasons.
– During the winter the poles increase in size.
– During the summer they decrease in size.
• The layering of the polar caps indicates that
there have been long term cyclical temperature
patterns on Mars.
– Similar to the ice ages of Earth
Martian Moons
• Small and irregularly shaped
• Why are they not spheres?
• Most likely they are asteroids that were
captured by the Martian gravity.
Explanation of Planetary
differences
• One major explanation of planetary
differences is the role of size and density.
• Small planets have cooler more solid
cores. As a result, they have little tectonic
activity.
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the moving of the crust, earthquakes, and
volcanic eruptions.
What is a result of tectonic activity?
• Tectonic activity causes the surface of a
planet to change. Craters formed by
asteroids are lost due to lava flows.
Dramatically shaping the planets surface
• If conditions are right, liquid water may form
and surface features may change even further
due to water erosion.
• Gases are released from volcanic eruptions
and form the atmosphere.
Planetary size and activity
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– small and tectonically inactive, no
atmosphere.
– Small – dead
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– slightly larger, evidence of an active
past, but currently non active and a limited
atmosphere.
– Medium – once active
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– largest of the terrestrial
planets, Hot liquid cores that result in tectonic
activity. Little to none of the original planetary crust
is evident, constantly being reshaped by erosion
and eruptions.
– Large – active
Distance from the Sun
• Distance from the Sun affects surface
temperature. This in turn determines if
matter will be a solid, liquid or a gas.
• Can also affect the atmosphere
• How high water molecules can be found
• If it is so hot gases will be able to escape.
Resulting in no atmosphere at all.
(Mercury)
The role of water content
• Water can be split into its parts by UV light. The
heavier Oxygen sinks back into the atmosphere,
and the lighter Hydrogen escapes into space.
– Photo dissociation – breaking up of water molecules
into H and O.
• As a result H concentration drops. On Venus
water vapor can be found high in the upper
atmosphere where it encounters UV light.
• On Earth because of a reduced greenhouse
effect, water vapor freezes at about 30,000 ft and
then sinks. It does not encounter the UV light and
therefore, H concentration on Earth is higher than
Venus.
Earth has been shaped by
biological processes
• Plants have added O2 to our atmosphere
by breaking down water molecules during
photosynthesis.
• Humans and other organisms have
shaped the planet surface by construction,
destruction, and altering patterns of
erosion.
Terrestrial Planet Test Review
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Order of planetary size
Difference between the planets
General information about each
planet (atm., volcanoes, etc.)
Why Mercury has no atm.
Why Mars has an atm.
Role of distance from Sun on
planetary characteristics
Differences in planetary
topography, and why
Role of water content in the atm.
Venus and its odd orbit, explain
Venus and its atm.
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Mars and its hydrological story
Greenhouse effects
Role of planet size, tectonics and
an atm.
Atm. Formation
UV light and water
Info from Mars Rovers movies
Rotation and magnatism
Are “manned” missions to Mars
or outer planets necessary?
• After reading the article address the question
• Include in your answer supporting statements indicating why they should be
manned or unmanned and the drawbacks of the opposing view.
• Indicate problems that may be encountered and how you would address
them.
• Example:
• I think that manned missions are need because of X, Y, and Z., unmanned
missions would limit us in these ways A,B,C. Manned missions would
encounter the following problems: 1,2,3. I would address these problems in
the following ways…