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The Planet Venus
Appearance of Venus
• The Moon and Mercury are geologically dead
• Venus, Earth, and Mars are still active geologically
• Venus is the planet nearest
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• Venus looks very bright to
to Earth, sometimes
approaching to within 40
million km
The orbit of Venus is
nearly circular at a
distance of 108 million km
(0.72 AU)
Venus is very bright in the
sky
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the naked eye and even a
small telescope shows that
Venus goes through phases
like the Moon
The surface of Venus is
always obscured by a very
dense cloud cover
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Reflects 70% of the sunlight
• Various bands are visible in
different wavelength light
“Evening star”
“Morning star”
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
1
Phases of Venus
ISP 205 - Astronomy Gary D. Westfall
Enhanced picture of Venus shot through
a violet filter by the Galileo spacecraft
Lecture 11
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Current Position of Venus and Mars
• Current position of inner planets, Oct. 4
• Venus appears to go through phases
• Different from Moon because distance changes
drastically
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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Basic Properties of Venus
The Atmosphere of Venus
• The atmosphere of Venus causes a very high surface
• Venus is the second planet from the Sun
• Venus is nearly the same size as Earth
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12,102 km in diameter(12,756 km for Earth)
82% the mass of Earth
Similar density, 5.3 g/cm3 (5.5 g/cm3 for Earth)
temperature and gives the surface a perpetual red twilight
The weather at the surface is hot, dry, calm
The pressure at the surface is 90 times the Earth’s
atmospheric pressure
Gas
%
• Venus takes 223 days to orbit the Sun
Carbon
Dioxide (CO2)
95.3
• Venus takes 2,243days to rotate on
Nitrogen (N2)
2.7
it axis and it rotates the opposite
direction of Earth
Argon (Ar)
1.6
Oxygen (O2)
0.15
Neon (Ne)
0.0003
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ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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ISP 205 - Astronomy Gary D. Westfall
Surface Temperature of Venus
• The atmosphere is the result of a runaway
greenhouse effect
800 degrees Fahrenheit
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• Caused by the greenhouse effect
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Venus has 1 million times more CO2 than Earth
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• Sunlight that diffuses through the atmosphere
been evaporated into water vapor
The surface heats up until the radiation of heat is the
same as the absorption of heat from the Sun
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• The dense atmosphere makes the temperature the
same everywhere on the surface of Venus
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Water vapor is also a greenhouse gas
Once in the atmosphere, UV from the Sun can break
up the water vapor into the constituent hydrogen and
oxygen
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Little weather
ISP 205 - Astronomy Gary D. Westfall
Not just a larger greenhouse effect like the increase in
CO2 in the Earth’s atmosphere
Irreversible
• If Venus had oceans like Earth, they would have
heats the surface and the CO2 acts as a blanket
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Implications for Earth
• The surface temperature of Venus is 700 K
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Lecture 11
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Lecture 11
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Hydrogen can then escape
Water is permanently gone
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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Probing Through the Clouds
The Magellan Mission to Venus
• The Magellan mission to Venus was launched May 4,
• Venus has been visited by several spacecraft
• Shown below is an image taken by the Russian
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spacecraft Venera 13 on the surface of Venus
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Venera 13 landed on the surface of Venus on March 1,
1982, survived 2 hours and 7 minutes and sent back 14
pictures
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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1989 and arrived at Venus on August 10, 1990
Magellan used a high resolution radar to map the surface
of Venus through the opaque clouds
Magellan worked for 4 years and mapped 98% of the
surface of Venus
ISP 205 - Astronomy Gary D. Westfall
Mapping the Surface of Venus
Lecture 11
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Craters on the Surface of Venus
• Dating the surface of a planet is
• The Magellan data can be processed into 3-D
views of the surface of Venus
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not the same as dating the entire
planet
The largest crater on Venus is
the Mead Crater
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Larger than the largest crater on
Earth
• The thick atmosphere of Venus
does not protect the surface
from impacts
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3-D view of three impact crater on the
surface of Venus
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Lecture 11
The Mead Crater - 280 km in diameter
Large projectile make it to the surface
There are few craters smaller than 10 km in diameter
• We can use craters with diameters greater the 30 km
False color picture of Venus constructed from radar
images from the Magellan space craft
ISP 205 - Astronomy Gary D. Westfall
Small projectiles burn up
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ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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Volcanoes on Venus
Implications for the Age of the Surface
• Venus is a planet with wide-scale volcanic activity
• In the lowland plains, lava renews the surface and erases
• There are only about 15% as many craters on the
plains of Venus as on the maria of the Moon
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Gives an age of about 500 million years
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• Indicates Venus has an active geological history
• All the craters look fresh
craters
The are many volcanoes associated with surface hot spots
The largest volcano on
Venus is Sif Mons
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No evidence of erosion be volcanic activity or wind
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• Little has happened since the plains of Venus
• These volcanoes result
were resurfaced by large scale volcanic activity
• Apparently Venus experienced a volcanic
calamity 500 million years ago
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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The Planet Mars
from magma reaching the
surface
Pressure under the surface
can cause bulges called
coronae
ISP 205 - Astronomy Gary D. Westfall
• To the naked eye, Mars appears to be a small, reddish star
• With a telescope, one can make out features on the
surface of Mars
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687 days (1.88 years)
• Mars has an eccentric
orbit (e = 0.09) with a
semimajor axis of 230
million km (1.52 AU)
• Mars rotates on its
axis every 24.6 hours
• Mars’ axis is tilted
25.2 degrees
With the best Earth-bound telescopes, we can make out features
on the order of 100 km, similar to the Moon with the naked eye
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Lecture 11
Computer generated 3-D view of Sif Mons using data
from Magellan
Lecture 11
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Appearance of Mars
• Mars is the fourth planet from the Sun
• Mars is the seventh largest planet
• Mars orbits the Sun in
ISP 205 - Astronomy Gary D. Westfall
3 km high, 500 km across
Caldera is 40 km across
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No topographical features visible
In 1877, the Italian astronomer Sciaperelli announced he saw
lines on Mars that he called canale which were mistakenly
translated as canals
This observation combined with the observation of the polar ice
caps, led to the idea that intelligent life existed on Mars
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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Lowell’s Canals
Spacecraft Exploration of Mars
• The American astronomer Lowell built an
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• The first visitor to Mars was Mariner 4
observatory in Flagstaff, Arizona and
concentrated on studying Mars
Lowell claimed he saw canals on Mars and that
these canals were evidence of intelligent life on
Mars
Most other observers could
not see the canals
The idea of canals on Mars
lasted into the 1930s
Sparked the idea of “Men
from Mars”
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
in 1965
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• Mariner 9 became the first spacecraft to
orbit another planet in 1971
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Lecture 11
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ISP 205 - Astronomy Gary D. Westfall
landers were sent to Mars
In 1997 less expensive
missions were begun
Lecture 11
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Main Surface Features
• There are four prominent surface features on Mars
the diameter of Earth
The density of Mars is 3.9 g/cm3, suggesting that
Mars has a small metallic core
Mars has no magnetic field
About half the surface consists of older, higher
elevation highlands that are highly cratered,
mainly in the southern hemisphere
The remaining half, mainly in the northern
hemisphere, consists of young lightly cratered
volcanic plains about 4 km lower than the
highlands
ISP 205 - Astronomy Gary D. Westfall
Photo taken by Mariner 4 showing first
unambiguous evidence for craters on Mars
• In 1976 two Viking
• The diameter of Mars is 6790 km, just over half
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Showed volcanoes, canyons, layered polar
caps, and channels that appeared to have
been cut by running water
Photo of the
caldera of
Olympus
Mons taken
by Mariner 9
Global Properties
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Showed a bleak planet with abundant
craters, no canals
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Olympus Mons: the largest mountain in the Solar System rising 24 km
(78,000 ft.) above the surrounding plain. Its base is more than 500 km in
diameter and is rimmed by a cliff 6 km (20,000 ft) high.
Tharsis: a huge bulge on the Martian surface that is about 4000 km across
and 10 km high.
Valles Marineris: a system
of canyons 4000 km long
and from 2 to 7 km deep (top
of page);
Hellas Planitia: an impact
crater in the southern
hemisphere over 6 km deep
and 2000 km in diameter.
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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Olympus Mons and Tharsis
Mariner Valley and Hellas Planitas
• This movie shows an
• Mariner Valley is
animation of the
Olympus Mons
caldera
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The opening is 65 km
across
3000 km long and 8
km deep
Animation shows a
fly-by along the
Valley
• This picture shows the
Tharsis bulge
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• The Hellas Impact
Contains 12 large
volcanoes
Crater history indicates
activity ceased 2
billion years ago
ISP 205 - Astronomy Gary D. Westfall
Basin is 2100 km
across and 9 km deep
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Lecture 11
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View in the Chryse Basin
CO2 frost is visible in
upper globe picture
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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View in the Utopia Planita
• Viking 2 landed in Utopia Planita
• Viking 1 and Pathfinder landed in the Chryse Basin which may
have held a shallow sea
Pathfinder
picture
showing
Sojourner
Viking 1
picture
showing
angular
rocks and
fine dust
Surface here is rockier and
less hilly than Chryse.
Many of the rocks were
ejected from nearby
impact crater.
Water-ice frost forms
during winter
Pathfinder picture showing wide angle view of Chryse Planita
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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The Sky on Mars
Martian Samples
• Pathfinder took pictures of the color of the sky on Mars
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• Martian meteorites have been found in Antarctica
• May have come from Mars as remnants of a large
Dust particles in the atmosphere give the sky a reddish tint
impact
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Noon on Mars
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Chemical composition matches
Trapped gasses match Martian composition
Some structures resemble fossilized life
Recent studies do not support those conclusions
Meteorite ALH84001 found in Antarctica
Sunset on Mars
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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ISP 205 - Astronomy Gary D. Westfall
The Moons of Mars
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Lecture 11
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Clouds on Mars
• The atmospheric pressure on Mars is less the 1%
• Mars has two moons (more later on these moons)
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Structures that resemble fossilized life
that of Earth
• Several type of clouds form in the atmosphere of
Mars
Deimos
Phobos
Water ice clouds
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Dust clouds
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Can reach planet-wide proportions
Water ice clouds
Carbon dioxide clouds
• Because of the low pressure on Mars, water
Dust storm
cannot exist as a liquid
Deimos
ISP 205 - Astronomy Gary D. Westfall
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Phobos
Lecture 11
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Ice goes directly from solid to gas
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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Polar Ice Caps
Water on the Surface of Mars
• Mars has polar ice caps
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existed on the surface of Mars
During winter, these ice caps can extend down to
latitude 50 degrees
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Permanent ice caps
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Water stays frozen at much higher temperatures than
frozen CO2
Huge reservoir of water the size of the Mediterranean
Sea
Two caps are different because of the
eccentricity of Mars’ orbit around the Sun
combined with the tile of Mars’ rotational
axis
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
Runoff channels
Outflow channels
• Where did the water come from?
Southern ice cap composed of CO2 and water
Northern ice cap composed of water
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• Some evidence shows that flowing water once
Seasonal ice caps are composed of frozen
CO2
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North polar cap
One idea is that frozen water under the surface melted
and flowed
Outflow network
South polar cap
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ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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