Transcript Venus and Mars

Venus
&
Mars
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Nearest Planets
Venus and Mars resemble
Earth more than any other
planets
But the three are very
different from each other
Venus and Mars are among
the brightest objects in the night sky
Intriguing questions:
Will we someday be able to visit
Venus or Mars?
Does alien life exists on either?
Can studying these planets give us
clues to Earth’s origin, or future?
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Venus
Mars
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Appearance of Venus
Venus gets closer to Earth (about 40 million
km) than does any other planet
Venus sometimes appears as a bright
object near the Sun after sunset (an “evening
star”) or before sunrise (a “morning star”)
Galileo discovered that
Venus goes through phases,
like the Moon
Venus is shrouded by thick
clouds, making it impossible
to view its surface, even
with cameras in orbit around
the planet
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Appearance of Mars
About every 24 months the Earth and Mars
are at their closest (~56 million km apart)
Mars is reddish due to the presence of iron
oxides (rust) in its soil
Around 1900, Percival Lowell thought he saw
canals on Mars!
It is now generally accepted that what he saw was
an optical illusion
Two faces of Mars
Mars has polar ice
caps, thin clouds,
and dust storms
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Rotation of Venus and Mars
The rotation (spinning) of Mars has been
measured by observing features on the planet
over a very long time, about 200 years
Mars’ sidereal rotation period is 24 h 37m 23s,
about 40 minutes longer than Earth’s
The rotation (spinning) of Venus is measured
using radar, but (unlike Mercury) the radar is
used to observe the motion of Venus’ surface
features
Venus’ sidereal rotation period is 243 days!
Surprise: Venus spins in a backward or retrograde
direction!!
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Properties of Earth, Venus, and Mars
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Terrestrial Planets
Mercury
Venus
Earth
Mars
Basic Properties
Venus
is similar to Earth in
size, mass, and high
geological activity
has a thick atmosphere
consisting mostly of
carbon dioxide (CO2)
has a surface pressure
almost 100 times
greater than Earth’s
has a very hot surface,
with temperature of
730 K (over 850° F)
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Mars
is rather small in mass
and size compared to
Earth
may have had
significant geological
activity in the past
has a thin atmosphere
may have had a thick
atmosphere and liquid
water in the past
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which could have
supported life
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The Geology of Venus
Venus being similar size and composition to
the Earth, we might expect the two planets to
have similar geology
This is partly true, but Venus does not exhibit
the same kind of plate tectonics as the Earth
To study Venusian geology, we needed to
make a global study of its surface
This task is made very difficult by its massive
atmosphere
The solution is to use a radar instrument to probe
through the thick clouds
More spacecraft have visited Venus than any
other planet
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Missions to Venus
Missions to Venus:
1962: U.S. Mariner 2
did a flyby
1970: Soviet Venera 7
Images taken by Venera 13
became the first craft to land
on Venus and broadcast back pictures for 23
minutes (before succumbing to the extreme heat)
1970s: more Venera probes made photographs as
well as analyzed the soil and atmosphere
1970s: U.S. Pioneer Venus orbiter made the first
crude global radar map
1980s: Soviet Venera 15 and 16 radar orbiters
made better radar maps
1991-1993: U.S. Magellan spacecraft made radar
maps from orbit, at a resolution of 100 m
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A Radar Map of Venus
An image of Venus made by the Magellan
spacecraft
Colors have been
added to indicate
elevation
Blue means low and
red high
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Impact Craters and Surface Age of Venus
Crater counting has been used to
estimate the age of Venusian
surface
The largest crater, called Meade,
is 275 km in diameter
Venus’s thick atmosphere seems
to stop only small projectiles
Very few craters smaller than 10 km
in diameter have been found
The counting of larger craters
suggests a surface age of
roughly 500 million years
This is a probable indication of
persistent geological activity
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Volcanoes on Venus
Significant volcanism
Largest volcano, called
Sif Mons, wider but lower
than Mauna Loa in Hawaii
Some volcanoes have
shapes like “pancake
domes”
Volcanic bulges called
coronae are common
Computer-generated view of Sif Mons
Pancake-dome volcanoes
These are produced by
hot magma from the
planet’s interior which
does not make it to the
surface
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Massive Atmosphere of Venus
The atmospheric composition is 96% carbon
dioxide (CO2), 3.5% nitrogen, and very little
else
The CO2 traps heat
on the planet via the
greenhouse effect
The surface of Venus
has a temperature
above 700 K (850°F)
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Birth of Venus
The backward rotation of Venus may have
been caused by a giant impact early in its
history
The massive atmosphere and high surface
temperature of Venus may have been caused
by runaway greenhouse effect
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Geology of Mars
Mars is more
hospitable than
Venus to humans,
making Mars more
interesting
Early missions to Mars:
1965: Mariner 4 fly by
1971: Mariner 9 was the first to orbit
1976: Vikings 1 and 2 landed
20 years passed with 2 failed missions
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Spacecraft Exploration of Mars
Recent missions:
1997: Pathfinder landed
and Mars Global Surveyor
orbited
2002: Another craft orbited
2004: 2 U.S., 1 European,
and 1 Japanese craft sent
Pathfinder
European and Japanese craft failed, but U.S.
landers (rovers) succeeded
Animation of
rovers’ flight to
Mars
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Global Properties of Mars
Mars’ diameter is half Earth’s
It probably has a small metal core, but no
magnetic field
Apparently the planet has no liquid material in
its core today
The Mars Global Surveyor has produced maps
of the entire planet, showing
Highlands and lowlands
Computer-generated
rendering of Olympus Mons
The highlands are thought
to be older than lowlands
Olympus Mons, the highest
peak in the solar system
Vallis Marineris, the largest
canyon in the solar system
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Topographic Maps of Mars
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Volcanoes on Mars
The lowland plains look similar to the
lunar maria
This suggests that the plains may have
formed 3 to 4 billion years ago
The largest volcanoes
are found on the
Tharsis area
3 of them are shown
at right
Olympus Mons is the
largest, larger than
Mauna Loa in Hawaii
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Martian Cracks and Canyons
Valles Marineris is the
largest canyon in the
solar system
formed by tectonic
cracking in the Tharsis
bulge
not by running water
It extends for about
5,000 km
similar to the distance
from L.A. to N.Y.
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Martian Atmosphere and Polar Caps
Its atmosphere is thin
like the thin air about 30 km above the Earth’s surface
composed mostly of CO2
plus about 3% nitrogen and 2% argon
Various types of clouds can form on Mars
Dust clouds, raised by winds
Water-ice clouds, similar to those on Earth
CO2 (dry ice) clouds
Mars has seasonal polar caps made of
CO2 (dry ice)
Mars also has permanent or residual polar caps
composed of frozen CO2 and water ice in the south
much larger and composed of water ice in the north
Liquid water on Martian surface is not possible today
due to its very low pressure and temperature
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Climate Change on Mars
Mars might have had a much thicker
atmosphere and milder climate in the past
The cold, dry Mars we see today may have
been the result of some sort of runaway
refrigerator effect
The surface gravity of Mars is smaller than that
of Venus or Earth
Atmospheric gases on Mars can escape into
space more easily than those on Venus or Earth
As more and more of the gases escaped into
space, the surface temperature gradually fell
Eventually the planet became so cold that
water froze out of the atmosphere, further
reducing its ability to retain heat
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Channels & Gullies on Mars
Geological features on Mars that appear to be
evidence of water erosion in the distant and
recent past have been seen:
runoff channels
outflow channels
gullies
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Is There Life on Mars ?
Video evidence
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Search for Life on Mars
Life as we know it needs water
If Mars had had water in the past, life
could have existed there
It could be that UV light has sterilized
the surface, but could microbes live
below?
Scientists have tried looking for signs of
life on Mars in a variety of ways, so far
with negative results
The search continues …
Mars rovers’ website
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