Venus:
Global warming gone bad
Earth & Venus: Sister planets?
Venus
Earth
Mass
5x1024 kg
6x1024 kg
a (semimajor axis)
0.7 AU
1 AU
T at surface ~750 K
~300 K
P at surface ~90 atm
~1 atm
atm
N2 and H2O CO2 and
composition clouds
H2SO4
clouds
What is
the boiling
Temp of
water?
How do we know Venus’s surface temperature?
How do we know Venus’s surface temperature?
high energy
low energy
short wavelength
long wavelength
“bluer”
“redder”
hot
cold
How do we know Venus’s surface temperature?
the Sun emits light
here. T=6000 K
Earth emits light
here. T=300 K
Venus emits light
here. T=750
Amount of light observed above the
atmosphere
How do we know what the clouds are made of?
Spectrum of
planet with no
atmosphere
Wavelength of light (in the
infrared)
Spectrum of
planet with no
atmosphere
Wavelength of light (in the
infrared)
Amount of light observed above the
atmosphere
Amount of light observed above the
atmosphere
How do we know what the clouds are made of?
Spectrum of
planet with
atmosphere
Wavelength at which a
molecule in the atmosphere
absorbs light
Wavelength of light (in the
infrared)
How do we know what the clouds are made of?
(Infrared light)
How did Venus get so hot?
Remember - all gases absorb light at specific
wavelengths.
“Greenhouse” gases (like carbon dioxide, water and
methane) like to absorb in the infrared wavelengths.
Planets emit light at infrared wavelengths (same as
human bodies).
Conclusio n? “Greenhouse” gases don’t lett the heat
from the planet escape.
How did Venus get so hot?
A planet with no atmosphere
Solar
radiation
comes in
Planetary surface
Planetary
radiation
goes out
How did Venus get so hot?
A planet with an atmosphere
Solar
radiation
comes in
The greenhouse
gases reradiate.
Some of the energy
goes towards the
surface.
Greenhouse gases
Planetary surface
Planetary
radiation
goes out, but
gets
absorbed
How do greenhouse gases get into the atmosphere?
Water: evaporation
CO2: vaporization of rocks,
release from traps,
vaporization of biotic material
(like fossil fuels), respiration
Methane: release from traps,
biology (bacteria, cows, rice)
Venus is an example of a “runaway greenhouse”.
rocks and water
vaporize and release
greenhouse gases
greenhouse gases
heat the surface of the
planet
Why was Venus hot in the first place?
Earth was also a “runaway greenhouse” at one point!
rocks and water
vaporize and release
greenhouse gases
greenhouse gases
heat the surface of the
planet
Why did the Earth cool, but Venus stay so hot?
Why did the Earth cool, but Venus stay so hot?
Ideas: Oceans?
Biology?
It probably has to do with water, but why the Earth
has water and Venus doesn’t is not well
understood. It MAY be that water allowed plate
tectonics to occur, and when the oceanic plates
subduct, they take CO2 with them.
The Surface of Venus
Venus’s surface can’t be viewed in visible light.
The atmosphere absorbs most visible light.
Radio light reaches the surface.
Venus’s surface was mapped with RADAR.
RADAR
instrument
surface
RADAR instruments can map topography.
Venus’s surface was mapped with RADAR.
RADAR
instrument
smooth
surface
rough
surface
RADAR instruments can determine roughness.
Venus’s surface was mapped with RADAR.
RADAR
instrument
Reflective surface
Absorptive
surface
RADAR instruments can determine reflectivity.
Venus’s has few small craters. Why?
Venus’s has few large craters. Why?
Venus’s has few small craters. Why?
Venus has a dense atmosphere.
Venus’s has few large craters. Why?
Venus’s surface is ‘young’.
How are craters on Venus different from craters on other
bodies?
the moon
Venus
Venus’s surface is covered with volcanic features.
How can you tell impact
craters from volcanic calderas?
What does the brightness
mean in these images?
Venus’s surface is covered with volcanic features.
Few craters have been altered by lava.
What does this mean?
If lava lies
over an
existing crater,
then the crater
came first.
Venus: Take-away messages
•Venus’s bulk properties (mass, size, distance from sun)
are similar to Earth.
•However, Venus’s atmosphere has a lot of CO2 and
therefore its surface is very hot.
•Exactly why Venus and Earth evolved in different ways is
not well understood, but is probably related to water.
•Volcanism is an important process on its surface, but may
not have been active recently.
•Venus’s entire surface is ‘young’, so some global
resurfacing event occurred.