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The Planet Venus
• The Moon and Mercury are geologically dead
• Venus, Earth, and Mars are still active geologically
• Venus is the planet nearest
•
•
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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
“Evening star”
“Morning star”
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
1
Appearance of Venus
• Venus looks very bright to
•
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

Reflects 70% of the sunlight
• Various bands are visible in
different wavelength light
ISP 205 - Astronomy Gary D. Westfall
Enhanced picture of Venus shot through
a violet filter by the Galileo spacecraft
Lecture 11
2
Phases of Venus
• 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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Current Position of Venus and Mars
• Current position of inner planets, Oct. 4
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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Basic Properties of Venus
• 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)
• Venus takes 223 days to orbit the Sun
• Venus takes 2,243days to rotate on
it axis and it rotates the opposite
direction of Earth
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
QuickT ime™ and a
decompressor
are needed to see thi s picture.
5
The Atmosphere of Venus
• The atmosphere of Venus causes a very high surface
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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
%
Carbon
Dioxide (CO2)
95.3
Nitrogen (N2)
2.7
Argon (Ar)
1.6
Oxygen (O2)
0.15
Neon (Ne)
0.0003
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
6
Surface Temperature of Venus
• The surface temperature of Venus is 700 K

800 degrees Fahrenheit
• Caused by the greenhouse effect

Venus has 1 million times more CO2 than Earth
• Sunlight that diffuses through the atmosphere
heats the surface and the CO2 acts as a blanket

The surface heats up until the radiation of heat is the
same as the absorption of heat from the Sun
• The dense atmosphere makes the temperature the
same everywhere on the surface of Venus
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Little weather
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
7
Implications for Earth
• The atmosphere is the result of a runaway
greenhouse effect
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
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
been evaporated into water vapor
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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
Hydrogen can then escape
 Water is permanently gone

ISP 205 - Astronomy Gary D. Westfall
Lecture 11
8
Probing Through the Clouds
• Venus has been visited by several spacecraft
• The first spacecraft to land on the surface was
• Shown below is an image taken by the Russian
spacecraft Venera 13 on the surface of Venus

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
9
The Magellan Mission to Venus
• The Magellan mission to Venus was launched May 4,
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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
Lecture 11
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Mapping the Surface of Venus
• The Magellan data can be processed into 3-D
views of the surface of Venus
3-D view of three impact crater on the
surface of Venus
False color picture of Venus constructed from radar
images from the Magellan space craft
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
11
Craters on the Surface of Venus
• Dating the surface of a planet is
•
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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Small projectiles burn up
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
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
12
Implications for the Age of the Surface
• 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
• Indicates Venus has an active geological history
• All the craters look fresh
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No evidence of erosion be volcanic activity or wind
• Little has happened since the plains of Venus 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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Volcanoes on Venus
• Venus is a planet with wide-scale volcanics activity
• In the lowland plains, lava renews the surface and erases
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craters
The are many volcanoes associated with surface hot spots
The largest volcano on
Venus is Sif Mons
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3 km high, 500 km across
Caldera is 40 km across
• These volcanoes result
•
from magma reaching the
surface
Pressure under the surface
can cause bulges called
coronae
ISP 205 - Astronomy Gary D. Westfall
Computer generated 3-D view of Sif Mons using data
from Magellan
Lecture 11
14
The Planet Mars
• Mars is the third planet from the Sun
• Mars is the seventh largest planet
• Mars orbits the Sun in
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
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
15
Appearance of Mars
• 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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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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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
16
Lowell’s Canals
• The American astronomer Lowell built an
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•
•
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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
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Spacecraft Exploration of Mars
• The first visitor to Mars was Mariner 4
in 1965
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Showed a bleak planet with abundant
craters, no canals
• Mariner 9 became the first spacecraft to
orbit another planet in 1971
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Showed volcanoes, canyons, layered polar
caps, and channels that appeared to have
been cut by running water
Photo taken by Mariner 4 showing first
unambiguous evidence for craters on Mars
• In 1976 two Viking
Photo of the
caldera of
Olympus
Mons taken
by Mariner 9
ISP 205 - Astronomy Gary D. Westfall
•
landers were sent to Mars
In 1997 less expensive
missions were begun
Lecture 11
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Global Properties
• The diameter of Mars is 6790 km, just over half
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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
Lecture 11
19
Main Surface Features
• There are four prominent surface features on Mars
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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
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Lecture 11
20
Olympus Mons and Tharsis
• This movie shows an
animation of the
Olympus Mons
caldera
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QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
The opening is 65 km
across
• This picture shows the
Tharsis bulge
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Contains 12 large
volcanoes
Crater history indicates
activity ceased 2
billion years ago
ISP 205 - Astronomy Gary D. Westfall
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
Lecture 11
21
Mariner Valley and Hellas Planitas
• Mariner Valley is
•
QuickTime™ and a
Sorenson Video decom pressor
are needed t o see t his picture.
3000 km long and 8
km deep
Animation shows a
fly-by along the
Valley
• The Hellas Impact
Basin is 2100 km
across and 9 km deep
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CO2 frost is visible in
upper globe picture
ISP 205 - Astronomy Gary D. Westfall
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
Lecture 11
22
View in the Chryse Basin
• 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
Pathfinder picture showing wide angle view of Chryse Planita
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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View in the Utopia Planita
• Viking 2 landed in Utopia Planita
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
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
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The Sky on Mars
• Pathfinder took pictures of the color of the sky on Mars
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Dust particles in the atmosphere give the sky a reddish tint
Noon on Mars
ISP 205 - Astronomy Gary D. Westfall
Sunset on Mars
Lecture 11
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Martian Samples
• Martian meteorites have been found in Antarctica
• May have come from Mars as remnants of a large
impact
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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
ISP 205 - Astronomy Gary D. Westfall
Structures that resemble fossilized life
Lecture 11
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The Moons of Mars
• Mars has two moons (more later on these moons)
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Deimos
Phobos
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Deimos
ISP 205 - Astronomy Gary D. Westfall
Phobos
Lecture 11
27
Clouds on Mars
• The atmospheric pressure on Mars is less the 1%
that of Earth
• Several type of clouds form in the atmosphere of
Mars
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
cannot exist as a liquid
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Dust storm
Ice goes directly from solid to gas
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
28
Polar Ice Caps
• Mars has polar ice caps
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Seasonal ice caps are composed of frozen
CO2
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During winter, these ice caps can extend down to
latitude 50 degrees
Permanent ice caps
Southern ice cap composed of CO2 and water
 Northern ice cap composed of water
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Water stays frozen at much higher temperatures than
frozen CO2
Huge reservoir of water the size of the Mediterranean
Sea
North polar cap
Two caps are different because of the
eccentricity of Mars’ orbit around the Sun
combined with the tile of Mars’ rotational axis
South polar cap
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
29
Water on the Surface of Mars
• Some evidence shows that flowing water once
existed on the surface of Mars
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Runoff channels
Outflow channels
• Where did the water come from?
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One idea is that frozen water under the surface melted
and flowed
Outflow network
ISP 205 - Astronomy Gary D. Westfall
Lecture 11
30
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