Venus
Printable
version
March
27, 2000
Announcements
-
Turn
in homework #4
-
Solutions
to homework #4 on web later today
-
Drop
date this Friday, March 31
-
Next
Honors section:
-
Wed
April 5 (weather permitting) probably at 7:30pm or later
Venus
Preview
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Venus
overview
-
Observing
Venus from Earth
-
Retrograde
rotation:
puzzle
-
CO2
in Venus' atmosphere causes greenhouse effect
-
Average
surface temperature hotter than Mercury's!
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Structure,
composition of Venus' atmosphere
-
History
of Venus' atmosphere
-
The
surface of Venus
-
no
plate tectonics
-
several
volcanos
-
some
local crust motions (vertical)
-
not
many craters
Venus
Overview
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Venus
is similar in size, density, surface gravity to Earth
Observing
Venus from Earth
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Venus reflects 76% of sunlight
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compare 12% for Mercury
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Mercury is closer to sun,
brighter
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Greatest elongations are
47 degrees
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visible for ~3 hours after
sunset or before sunrise
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easier to see than Mercury
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Ring-like appearance at inferior
conjunction evidence for atmosphere
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similar to why moon turns
orange in lunar eclipse
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Featureless ball to optical
earth telescopes
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evidence for complete cloud
cover
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high albedo (reflectance)
also evidence for clouds
Retrograde
Rotation
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Venus rotates backwards
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Retrograde rotation is unusual
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Uncertain of cause
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formation likely prograde
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hit by planetesimal?
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sidereal period 243.01 earth
days (slow!)
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orbital period 224.70
Structure
and Composition of Atmosphere
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US and Soviet unmanned space
probe visits since 1960s
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Thick atmosphere
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90 times more pressure at
surface than Earth!
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Like being 1000 m deep in
ocean
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Clouds confined to 20 km
layer ~60 km from surface
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20 km thick haze layers above
and below clouds
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Temperature profile simpler
than Earth's
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Sulfur rich atmosphere, very
little water
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Instead of water droplet
clouds, sulfuric acid clouds!
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Acid eats spacecraft
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Circulation simpler than
Earth's because of slow rotation
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Convection driven by cloud
layer
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hot air rises at equator,
cools, falls at poles
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the rest of the atmosphere
pushed by that motion
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Upper atmosphere rotates
around planet in 4 days!
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East to west, pushes on clouds
to make < shapes
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Upper atmosphere winds 220
mi/hr
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Surface winds 3 mi/hr
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slowed by friction with surface
History
of Venus' Atmosphere
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Similar orbit and planet
size to Earth, probably started the same
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Sun may have been 70% cooler
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Venus may have had water
oceans
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Made water clouds, which
helped trap heat (greenhouse effect on Venus and Earth)
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On Earth, life started Early,
plants absorbed CO2, gave off Oxygen, Ozone layer formed
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Venus closer to sun, a little
warmer, not rotating as fast...
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On Venus, no life, or life
didn't make it, lots of CO2 in atmosphere, no Ozone
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As Sun warmed up, Venus got
hotter
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oceans started to evaporate
more
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more clouds
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more greenhouse effect
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...runaway greenhouse effect
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Evaporated all water on Venus
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At top of atmosphere, sunlight
breaks water up
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Hydrogen escapes (too little
gravity--same on Earth)
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High temperatures bake CO2
out of rocks
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CO2 contributes
to greenhouse effect, replaced water as reflecting blanket
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On Earth, CO2
absorbed by plants and chemical reactions with water and rocks that
form carbonate rocks like limestone
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Plate tectonics on Earth
can expose fresh rock
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Formation of Himalayas may
have caused last ice age
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Venus has no plate tectonics
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Earth has life, Venus does
not
Surface
of Venus
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Venus
has several volcanoes
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hot
spot volcanism
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active
in at least the last 10 million years
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Varying
levels of sulfur in atmosphere
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volcanoes
may be currently active
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Much
of surface seems to have been covered with lava
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broken
crust seen at landing site
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long
lava channel
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relatively
few craters
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Many
crust fractures
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Pancake
domes, corona
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crust
may be thinner than Earth's
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Two
"continents"
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Ishtar
terra
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Aphrodite
terra
Venus
Summary
-
Venus
overview
-
Observing
Venus from Earth
-
Retrograde
rotation:
puzzle
-
CO2
in Venus' atmosphere causes greenhouse effect
-
Average
surface temperature hotter than Mercury's!
-
Structure,
composition of Venus' atmosphere
-
History
of Venus' atmosphere
-
The
surface of Venus
-
no
plate tectonics
-
several
volcanos
-
some
local crust motions (vertical)
-
not
many craters