Venus and Mars Guidepost Guidepost (continued) Outline Venus

1
Venus and Mars
2
Guidepost
We have grouped the Earths moon and Mercury
together because they are similar worlds. In this
program we group Venus and Mars together because
we might expect them to be similar. They are
Earthlike in their size and location in the solar
system, so it is astonishing to see how different
they actually are. Much of this presentation is
aimed at understanding how Venus and Mars evolved
to their present states.
3
Guidepost (continued)
Neither Venus nor Mars can tell us much about the
formation of the planets. Both planets have
evolved since they formed. Nevertheless, we find
further hints that the solar system was a
dangerous place, with major impacts smashing the
surfaces of the planets, a process we first
suspected when we studied the moon and Mercury.
This chapter concludes our exploration of the
Earthlike worlds. In the next two chapters, we
will visit planets that give new meaning to the
word unearthly.
4
Outline
I. Venus A. The Rotation of Venus B. The
Atmosphere of Venus C. The Venusian
Greenhouse D. The Surface of Venus E. Volcanism
on Venus F. A History of Venus II. Mars A. The
Canals of Mars B. The Atmosphere of Mars C. The
Geology of Mars D. Hidden Water on Mars E. A
History of Mars III. The Moons of Mars A.
Origin and Evolution
5
Venus and Mars
Two most similar planets to Earth

• Similar in size and mass

• Atmosphere

• Similar interior structure

• Same part of the solar system

Yet, no life possible on either one of them.
6

• EARTH
  
• Distance from Sun 1.00 AU (1.495979 X 108 km
• Eccentricity 0.0167
• Aphelion 1.0167 AU
• Perihelion 0.9833 AU
• Orbit inclination 0o
• Average Orbital Velocity 29.79 km/sec
• Orbital Period 1.00 y (365.26 days)
• Period of rotation 24h 00m 00s
• Obliquity 23o 27
• Equatorial Diameter D ? 12,756 km (1.0 Dearth)
• Mass 5.976 X 1024 kg (1.0 Mearth)
• Average Density 5.497 g/cm3 (4.07 g/cm3 uncomp)
• Surface Gravity 1.0 gearth
• Escape Velocity 11.2 km/sec (1.0 Vearth)
• Surface Temperature 300 K (-50o to 50 oC, -60o
  to 120 oF)
• Albedo 0.39
• Oblateness 0

7

• VENUS
  
• Distance from Sun 0.7233 AU
• Eccentricity 0.0068
• Aphelion 0.7282 AU
• Perihelion 0.7184 AU
• Orbit inclination 3o 23 40
• Average Orbital Velocity 35.03 km/sec
• Orbital Period 0.61515 y (224.68 days)
• Period of rotation 243.01 days (retrograde)
• Obliquity 177o
• Equatorial Diameter D ? 12,104 km (0.95 Dearth)
• Mass 4.80 X 1024 kg (0.815 Mearth)
• Average Density 5.24 g/cm3 (4.2 g/cm3 uncomp)
• Surface Gravity 0.903 gearth
• Escape Velocity 10.3 km/sec (0.92 Vearth)
• Surface Temperature 745 K (472 oC, 882 oF)
• Albedo 0.76
• Oblateness 0

8
Planetary Atmospheres
(SLIDESHOW MODE ONLY)
9
The Rotation of Venus

• Almost all planets rotate counterclockwise, i.e.
  in the same sense as orbital motion.

• Exceptions Venus, Uranus and Pluto

• Venus rotates clockwise, with period slightly
  longer than orbital period.

Possible reasons

• Off-center collision with massive protoplanet

• Tidal forces of the sun on molten core

10
The Atmosphere of Venus
4 thick cloud layers (? surface invisible to us
from Earth).
UV image
UV image
Very stable circulation patterns with high-speed
winds (up to 240 km/h)
Extremely inhospitable
96 carbon dioxide (CO2)
Very efficient greenhouse!
3.5 nitrogen (N2)
Rest water (H2O), hydrochloric acid (HCl),
hydrofluoric acid (HF)
Extremely high surface temperature up to 745 K
( 880 oF)
11
The Surface of Venus
Early radar images already revealed mountains,
plains, craters.
More details from orbiting and landing spacecraft
Venera 13 photograph of surface of Venus
Colors modified by clouds in Venuss atmosphere
After correction for atmospheric color effect
12
Radar Map of Venus Surface
Surface features shown in artificial colors

• Scattered impact craters

• Volcanic regions

• Smooth lava flows

13
Lava Flows
Young, uneven lava flows (shown Lava flow near
Flagstaff, AZ) show up as bright regions on radar
maps.
14
Surface Features on Venus
Highland regions
Maxwell Montes are 50 higher than Mt. Everest!
Smooth lowlands
15
Craters on Venus
Nearly 1000 impact craters on Venuss surface
? Surface not very old.
No water on the surface thick, dense atmosphere
? No erosion
? Craters appear sharp and fresh
16
Volcanism on Earth
Volcanism on Earth is commonly found along
subduction zones (e.g., Rocky Mountains).
This type of volcanism is not found on Venus or
Mars.
17
Shield Volcanoes
Found above hot spots
Fluid magma chamber, from which lava erupts
repeatedly through surface layers above.
All volcanoes on Venus and Mars are shield
volcanoes
18
Shield Volcanoes (2)
Tectonic plates moving over hot spots producing
shield volcanoes ? Chains of volcanoes
Example The Hawaiian Islands
19
Hotspot Volcanoes
(SLIDESHOW MODE ONLY)
20
Volcanism on Venus
Sapas Mons (radar image)
400 km (250 miles)
2 lava-filled calderas
Lava flows
21
Volcanic Features on Venus
Aine Corona
Baltis Vallis 6800 km long lava flow channel
(longest in the solar system!)
Coronae Circular bulges formed by volcanic
activity
Some lava flows collapsed after molten lava
drained away
Pancake Domes
Associated with volcanic activity forming coronae
22
Lakshmi Planum and Maxwell Mountains
Radar image
Wrinkled mountain formations indicate compression
and wrinkling, though there is no evidence of
plate tectonics on Venus.
23
MAGNETOSPHERE
? Solar wind interacts directly with the
atmosphere, forming a bow shock and a long ion
tail.
24
A History of Venus

• Complicated history still poorly understood.
• Very similar to Earth in mass, size, composition,
  density,
• but no magnetic field ? Core solid?
• CO2 produced during outgassing remained in
  atmosphere (on Earth dissolved in water).
• Any water present on the surface rapidly
  evaporated ? feedback through enhancement of
  greenhouse effect
• Heat transport from core mainly through magma
  flows close to the surface (? coronae, pancake
  domes, etc.)

25
Mars

• Diameter 1/2 Earths diameter

• Very thin atmosphere, mostly CO2

• Rotation period 24 h, 40 min.

• Axis tilted against orbital plane by 25o,
  similar to Earths inclination (23.5o)

• Seasons similar to Earth ? Growth and shrinking
  of polar ice cap

• Crust not broken into tectonic plates

• Volcanic activity (including highest volcano in
  the solar system)

26
Tales of Canals and Life on Mars
Early observers (Schiaparelli, Lowell) believed
to see canals on Mars
This, together with growth/shrinking of polar
cap, sparked imagination and sci-fi tales of life
on Mars.
We know today canals were optical illusion do
not exist!
No evidence of life on Mars.
27

• Mars
• Distance from Sun 1.5237 AU
• Eccentricity 0.0934
• Aphelion 1.6660 AU
• Perihelion 1.3814 AU
• Orbit inclination 1o 51 09
• Average Orbital Velocity 24.13 km/sec
• Orbital Period 1.8808 y (686.95 days)
• Period of rotation 24h 37m 22.6
• Obliquity 25o 19
• Equatorial Diameter D 6796 km (0.53 Dearth)
• Mass 0.6424 X 1024 kg (0.1075 Mearth)
• Average Density 3.94 g/cm3 (3.3 g/cm3 uncomp)
• Surface Gravity 0.379 gearth
• Escape Velocity 5.0 km/sec (0.45 Vearth)
• Surface Temperature -140o to 20 oC, (-220o to 68
  oF)
• Albedo 0.16
• Oblateness 0.009

28
The Atmosphere of Mars
Very thin Only 1 of pressure on Earths surface
95 CO2
Even thin Martian atmosphere evident through haze
and clouds covering the planet
Occasionally Strong dust storms that can
enshroud the entire planet.
29
The Atmosphere of Mars (2)
Most of the Oxygen bound in oxides in rocks
? Reddish color of the surface
30
History of Marss Atmosphere
Atmosphere probably initially produced through
outgassing.
Loss of gasses from a planets atmosphere
Compare typical velocity of gas molecules to
escape velocity
Gas molecule velocity greater than escape
velocity ? gasses escape into space.
Mars has lost all lighter gasses retained only
heavier gasses (CO2).
31
The Geology of Mars
Giant volcanoes
Valleys
Impact craters
Reddish deserts of broken rock, probably smashed
by meteorite impacts.
Vallis Marineris
32
The Geology of Mars (2)
Northern Lowlands Free of craters probably
re-surfaced a few billion years ago.
Possibly once filled with water.
Southern Highlands Heavily cratered probably 2
3 billion years old.
33
Volcanism on Mars
Volcanoes on Mars are shield volcanoes.
Olympus Mons
Highest and largest volcano in the solar system.
34
Volcanism on Mars (2)
Tharsis rise (volcanic bulge)
Nearly as large as the U.S.
Rises 10 km above mean radius of Mars.
Rising magma has repeatedly broken through crust
to form volcanoes.
35
Hidden Water on Mars
No liquid water on the surface Would evaporate
due to low pressure.
But evidence for liquid water in the past
Outflow channels from sudden, massive floods
Collapsed structures after withdrawal of
sub-surface water
Splash craters and valleys resembling meandering
river beds
Gullies, possibly from debris flows
Central channel in a valley suggests long-term
flowing water
36
Hidden Water on Mars (2)
Gusev Crater and Maadim Vallis
Giant lakes might have drained repeatedly through
the Maadim Vallis into the crater.
37
Ice in the Polar Cap
Polar cap contains mostly CO2 ice, but also water.
Multiple ice regions separated by valleys free of
ice.
Boundaries of polar caps reveal multiple layers
of dust, left behind by repeated growth and
melting of polar-cap regions.
38
Evidence for Water on Mars
Galle, the happy face crater
Meteorite ALH84001
Identified as ancient rock from Mars.
Some minerals in this meteorite were deposited in
water ? Martian crust must have been richer in
water than it is today.
Large impacts may have ejected rocks into space.
39
The Moons of Mars
Two small moons Phobos and Deimos.
Too small to pull themselves into spherical shape.
Typical of small, rocky bodies Dark grey, low
density.
Phobos
Very close to Mars orbits around Mars faster
than Mars rotation.
Probably captured from outer asteroid belt.
Deimos
40
New Terms
subsolar point composite volcano shield
volcano corona outflow channel valley network  
41
Discussion Questions
1. From what you know of Earth, Venus, and Mars,
do you expect the volcanoes on Venus and Mars to
be active or extinct? Why? 2. If humans
someday colonize Mars, the biggest problem may be
finding water and oxygen. With plenty of solar
energy beating down through the thin atmosphere,
how might colonizers extract water and oxygen
from the Martian environment?
42
Quiz Questions
1. Why do larger and more massive planets take
longer to cool? a. Larger planets have a greater
mass-to-surface area ratio and therefore cool
more slowly. b. The more mass a planet has, the
greater is its heat of formation. c. The more
mass a planet has, the more heat-producing
radioactive elements it has. d. The more mass a
planet has, the thicker is its insulating
blanket. e. All of the above.
43
Quiz Questions
2. Why might we expect Venus and Earth to be
similar? a. Both planets are about the same size
and density. b. Both planets have about the same
chemical composition. c. Both planets have about
the same atmospheric composition. d. Both a and b
above. e. All of the above.
44
Quiz Questions
3. Why might Venus have the slow retrograde
rotation we see today? a. A large off-center
impact may have set Venus to spinning
backwards. b. The long-term effect of solar tides
on its dense atmosphere may be responsible. c.
The tidal effect of Earth on Venus may have spun
Venus backwards. d. Both a and b above. e. All of
the above.
45
Quiz Questions
4. What evidence do we have that Venus once had
more water than at present? a. We find dry
lakebeds on the surface of Venus. b. We find dry
riverbeds on the surface of Venus. c. The
deuterium hydrogen ratio in the atmosphere of
Venus is about 150 times that of Earth. d. Both a
and b above. e. All of the above.
46
Quiz Questions
5. Which gas is most abundant in the atmospheres
of Venus and Mars? a. Oxygen (O2). b. Nitrogen
(N2). c. Argon (Ar). d. Carbon dioxide (CO2). e.
Methane (CH4).
47
Quiz Questions
6. Why is the surface temperature of Venus higher
than that of any other planet? a. Its period of
rotation is longer than that of any other
planet. b. Its orbit is more nearly circular than
that of any other planet. c. It has an extreme
greenhouse effect. d. It is the closest planet to
the Sun. e. It has a retrograde rotation.
48
Quiz Questions
7. Why are the surface temperatures of Venus and
Earth so very different? a. Venus is too close
to the Sun to have liquid water oceans. b. Earth
is far enough from the Sun to have liquid water
oceans. c. The ozone layer of Earth shields the
surface from ultraviolet radiation. d. Both a and
b above. e. All of the above.
49
Quiz Questions
8. How do we know what the surface of Venus looks
like? a. Large Earth-based optical telescopes
have photographed the surface. b. The high
resolution of the Hubble Space Telescope reveals
the surface details. c. Radar mapping at radio
wavelengths allows us to determine surface
elevations. d. Orbiting spacecraft have imaged
the surface at ultraviolet and infrared
wavelengths. e. Two spacecraft that entered the
atmosphere of Venus released balloons that
floated just beneath the cloud deck and mapped
the surface.
50
Quiz Questions
9. Why do you suppose that the smallest impact
craters on the Moon are microscopic, the smallest
on Earth are dozens of meters in diameter, and
the smallest on Venus are more than one kilometer
in diameter? a. The Moon has no atmosphere and
Venus has an atmosphere much more dense than
Earth's. b. Atmospheric gases easily slow the
speed of smaller incoming meteoroids. c. Venus is
farther away from the asteroid belt. d. Both a
and b above. e. All the above.
51
Quiz Questions
10. All of the dormant volcanoes on Venus and
Mars are the shield type, and many are much
larger than any shield volcano on Earth. What
does this tell us about Venus and Mars? a. Venus
and Mars both have plate tectonics b. Neither
Venus nor Mars has plate tectonics. c. Their
interiors are at a higher temperature than
Earth's interior. d. Their interiors are at a
lower temperature than Earth's interior. e. Venus
and Mars both have carbon dioxide atmospheres
52
Quiz Questions
11. Planets that have strong magnetic fields also
have rapid rotation and convective fluid interior
zones that are good electrical conductors. The
magnetic field of Venus is so weak that it has
not yet been detected, which makes it at least
25,000 times weaker than Earth's magnetic field.
Examine the Venus data file on page 473. What
information here may indicate why Venus is
lacking a strong magnetic field? a. The
eccentricity of orbit 0.0068. b. Inclination of
orbit to ecliptic 3 degrees, 23 arc minutes, 40
arc seconds. c. Period of rotation 243.01 days
(retrograde). d. Average density 5.24 grams per
cubic centimeter. e. Surface temperature 745 K
(472ºC or 882ºF).
53
Quiz Questions
12. What determines whether an atmospheric gas
can be retained by a planet, rather than be lost
to space? a. The escape speed of the planet. b.
The mass of the gas atoms or molecules. c. The
temperature of the planet's upper atmosphere. d.
Both a and b above. e. All of the above.
54
Quiz Questions
13. What evidence do we have that the Martian
atmosphere was denser in the past than it is
today? a. The abundance of argon by mass is
1.6. b. The observed dry streambeds and outflow
channels. c. Mars is a small body and light gases
can easily escape. d. Both a and b above. e. All
of the above.
55
Quiz Questions
14. Evidence suggests that Mars had a greater
abundance of atmospheric carbon dioxide in the
past than it has today. How could Mars have lost
some of its atmospheric carbon dioxide? a. Some
carbon dioxide solidified and is part of the
polar ice caps. b. The solar wind can ionize and
strip gas molecules from the upper atmosphere. c.
The weak gravity field of Mars cannot easily hold
onto carbon dioxide molecules. d. Both a and b
above. e. All of the above.
56
Quiz Questions
15. Measurements from orbiting spacecraft suggest
that Mars had a magnetic field in its past. How
could Mars lose its magnetic field? a. Mars has
cooled to the point that it no longer has a fluid
interior. b. The rotation of Mars was once
retrograde and now is in the prograde
direction. c. Mars rate of rotation has slowed
such that it now has tidal coupling with the
Sun. d. Both a and b above. e. All of the above.
57
Quiz Questions
16. What evidence do we have that Mars had much
more liquid water at its surface in the past than
it has today? a. The deuterium-hydrogen ratio is
5.5 times as high as on Earth. b. Martian
meteorites must have formed from lava that was
nearly 2 water. c. We see large, dry outflow
channels and valley networks on the surface of
Mars. d. Both a and b above. e. All of the above.
58
Quiz Questions
17. How do we know that the slope gullies found
in recent images are younger than both the
outflow channels and the valley networks? a.
These gullies did not appear in the Viking images
of 1976, and thus must have formed in recent
years. b. The outflow channels and valley
networks have a higher density of impact
craters. c. The gullies are darker, indicating
that the soil along their floors is still wet. d.
The gullies are smaller than the outflow channels
and valley networks. e. The outflow channels and
valley networks are larger than the gullies.
59
Quiz Questions
18. What do we now believe is responsible for the
seasonal changes that were seen on Mars through
Earth-based telescopes over the past century or
two? a. These changes are optical illusions. b.
These changes are due to seasonal global dust
storms on Mars. c. These are seasonal plant life
cycles in the plains and forests of Mars. d.
These are long linear faults that break open then
close due to the freezing and thawing of ground
water. e. These changes are due to global
volcanic activity that creates new shield
volcanoes and fresh lava plains.
60
Quiz Questions
19. A large high-mass terrestrial planet cools
more slowly than a small low-mass terrestrial
planet. The outward flow of heat drives surface
activity for a longer period of time on larger
bodies. Thus, today we expect to find a lower
density of impact craters on larger bodies. Use
this information to predict the order of the
terrestrial planets from lowest density of impact
craters to the highest density of impact
craters. a. Mercury, Venus, Earth, Mars. b.
Mercury, Mars, Venus, Earth. c. Earth, Mercury,
Mars, Venus. d. Mars, Earth, Mercury, Venus. e.
Earth, Venus, Mars, Mercury.
61
Quiz Questions
20. Why are Phobos and Deimos not spherical? a.
They are the two halves of a once spherical
body. b. Their gravity fields are too weak to
pull their material into a spherical shape. c.
They were spherical at one time and have accreted
a few large rocky blocks that hide their original
shape. d. They were originally spherical and have
suffered many small random collisions that give
them a chiseled appearance. e. The non-spherical
shape suggests that they skimmed the atmosphere
of Mars during the capture event and were shaped
by the encounter.