Transcript of Chapter 6 The Terrestrial Planets. Units of Chapter 6 Orbital and Physical Properties Rotation Rates...
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- Chapter 6 The Terrestrial Planets
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- Units of Chapter 6 Orbital and Physical Properties Rotation
Rates Atmospheres The Surface of Mercury The Surface of Venus The
Surface of Mars Internal Structure and Geological History
Atmospheric Evolution on Earth, Venus, and Mars Summary of Chapter
6
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- 6.1 Orbital and Physical Properties The orbits of Venus and
Mercury show that these planets never appear far from the Sun.
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- The terrestrial planets have similar densities and roughly
similar sizes, but their rotation periods, surface temperatures,
and atmospheric pressures vary widely.
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- 6.2 Rotation Rates Mercury can be difficult to image from
Earth; rotation rates can be measured by radar.
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- Mercury was long thought to be tidally locked to the Sun;
measurements in 1965 showed this to be false. Rather, Mercurys day
and year are in a 3:2 resonance; Mercury rotates three times while
going around the Sun twice.
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- Venus Mars
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- All the planets rotate in a prograde direction, except Venus,
which is retrograde.
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- 6.3 Atmospheres Mercury has no detectable atmosphere; it is too
hot, too small, and too close to the Sun. Venus has an extremely
dense atmosphere. The outer clouds are similar in temperature to
Earth, and it was once thought that Venus was a jungle planet. We
now know that its surface is hotter than Mercurys, hot enough to
melt lead. The atmosphere of Mars is similar to Earth in
composition, but very thin.
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- Mercury cannot be imaged well from Earth; best pictures are
from Messenger. Cratering on Mercury is similar to that on the
Moon. 6.4 The Surface of Mercury
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- Some distinctive features: Scarp (cliff), several hundred km
long and up to 3 km high, thought to be formed as the planet cooled
and shrank.
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- Caloris Basin, very large impact feature; ringed by concentric
mountain ranges
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- 6.5 The Surface of Venus This map of the surface features of
Venus is on the same scale as the Earth map below it.
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- Venus as a globe, imaged by Magellan
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- Top: Lava domes on Venus (L), and a computer reconstruction (R)
Bottom: the volcano Gula Mons
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- Venus corona, with lava domes
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- A photograph of the surface, from the Venera lander
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- Impact craters. Left: multiple-impact crater Above: Mead,
Venuss largest impact crater
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- 6.6 The Surface of Mars Major feature: Tharsis bulge, size of
North America and 10 km above surroundings Minimal cratering;
youngest surface on Mars
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- Northern hemisphere (left) is rolling volcanic terrain.
Southern hemisphere (right) is heavily cratered highlands; average
altitude 5 km above northern. Assumption is that northern surface
is younger than southern. Means that northern hemisphere must have
been lowered in elevation and then flooded with lava.
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- This map shows the main surface features of Mars. There is no
evidence for plate tectonics.
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- Mars has largest volcano in Solar System; Olympus Mons: 700 km
diameter at base 25 km high Three other Martian volcanoes are only
slightly smaller. Caldera 80 km in diameter
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- Was there running water on Mars? Runoff channels resemble those
on Earth. Left: Mars Right: Earth
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- No evidence of connected river system; features probably due to
flash floods
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- This feature may be an ancient river delta. Or it may be
something entirely different.
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- Much of northern hemisphere may have been ocean.
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- Impact craters less than 5 km across have mostly been eroded
away. Analysis of craters allows estimation of age of surface.
Crater on right was made when surface was liquid.
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- Recently, gullies have been seen that seem to indicate the
presence of liquid water; interpretation is still in doubt.
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- 6.7 Internal Structure and Geological History Internal
structure of Mercury, Mars, and the Moon, compared to Earth
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- 6.8 Atmospheric Evolution on Earth, Venus, and Mars At
formation, planets had primary atmosphere hydrogen, helium,
methane, ammonia, water vapor which was quickly lost. Secondary
atmosphere water vapor, carbon dioxide, sulfur dioxide, nitrogen
comes from volcanic activity. Earth now has a tertiary atmosphere,
20 percent oxygen, due to the presence of life.
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- Earth has a small greenhouse effect; it is in equilibrium with
a comfortable (for us) surface temperature.
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- Venuss atmosphere is much denser and thicker; a runaway
greenhouse effect has resulted in its present surface temperature
of 730 K.
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- the density of Mars is: A about like that of the Earth. B the
lowest of the terrestrial planets. C the lowest of all planets. D
the greatest of the terrestrial planets.
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- the rotational period of Venus was measured by A watching
surface features move across the planet's disk B measuring the
speed of clouds in the planet's atmosphere C measuring the Doppler
shift of radar signals bounded off the planet's surf D orbiting
spacecraft around the planet
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- a major feature of the atmosphere of Mars is A very dense
clouds shrouding most of the planet B strong winds and dust storms
C very high temperatures and pressures D chemical mixture very
similar to that of Earth
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- the average surface temperature of Venus is: A about like that
on Earth. B a bit warmer than that on Earth. C extremely hot
because of a runaway greenhouse effect. D unknown since we have not
explored the surface of Venus.
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- Venus' magnetic field produces which of the following A strong
lightning discharges B strong auroral activity C a connection
between the surface of Venus and that of its satellite D none of
the above, since Venus has no significant magnetic field
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- comparing the interiors of the Earth and Mars, we can infer
that A the Earth has a larger core of rocky materials. B Mars has a
larger core of rocky materials. C the Earth has a larger core of
metallic materials. D Mars has a larger core of metallic
materials.
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- Mercury is tidally locked in a 3:2 ratio with the Sun. Mercury
has no atmosphere; Venus has a very dense atmosphere, whereas the
atmosphere of Mars is similar to Earth in composition but very
thin. Mercury has no maria, but does have extensive intercrater
plains and scarps. Summary of Chapter 6
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- Summary of Chapter 6, cont. Venus is never too far from the
Sun, and is the brightest object in the sky (after the Sun and
Moon). It has many lava domes and shield volcanoes. Venus is
comparable to Earth in mass and radius. Large amount of carbon
dioxide in atmosphere, and closeness to the Sun, led to runaway
greenhouse effect and very hot surface.
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- Northern and southern hemispheres of Mars are very different.
South is higher and heavily cratered. North is lower and relatively
flat. Major features: Tharsis bulge, Olympus Mons, Valles Marineris
Strong evidence for water on Mars in the past Summary of Chapter 6,
cont.
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- Mercury has very weak, remnant magnetic field. Venus has none,
probably because of very slow rotation. Neither Venus nor Mars show
signs of substantial tectonic activity. Summary of Chapter 6,
cont.