Transcript powerpoint - Physics @ IUPUI

Goal: To understand the
differences between Venus and
Earth
To learn about how Venus’s atmosphere is
strange.
2) To understand what caused Venus’s atmosphere
to be so strange.
3) To Probing the surface and to understand what can
learn from that.
4) To examine the strange surface features of Venus.
5) To discover what is missing from the surface of
Venus and what that tells us about Venus.
1)
Venus!
• Same size and
composition as
the earth.
• 25% closer to
the sun.
• Vastly
different!
Probing Venus:
• First probe sent by Russia in 1959 (shortly
after Sputnik).
• The first few attempts failed…
• Venera 3 landed in 1965, but was
destroyed on impact.
• Venera 4 in 1967 parachuted to the
surface, but crushed before it reached the
surface (at altitude of 25 km).
More probes
• By 1970, and Venera 7, Russia made a
probe which could withstand higher
temperatures for a short time period.
• The temperature was measured at 748K!
Venus’s current atmosphere:
• Carbon Dioxide 96.5%
(vs 0.03% on the earth)
• Nitrogen 3.5%
• Water Vapor 0.003%
• Sulfur Dioxide 0.015%
• Surface pressure: 90 bars!
• Which planet has more total Nitrogen in its
atmosphere, Venus or Earth?
Nitrogen?
• Earth has 78% Nitrogen in its atmosphere.
At 1 bar total atmosphere that is 0.78 bars
worth of Nitrogen.
• It would seem that Earth should have
move. However…
• 90 bars * 0.03 = 2.7 bars.
• Venus has almost 4X more Nitrogen that
Earth.
Where did it go?
• Where is Earth’s Nitrogen?
Where did it go?
• Where is Earth’s Nitrogen?
• On earth, it is locked up in the crust by
living organisms (after all fertilizer is
mostly Nitrogen).
So, what is the consequence of this
atmosphere?
• Carbon dioxide is a greenhouse gas!
• On Venus the atmosphere is so thick that
effectively you have more than 1 greenhouse
layer.
• The lowest layer is heated by the layer above it,
and when it radiates energy, half goes to the
surface, and half goes to the layer above.
• The layer above absorbs that, then emits energy
half down to the layer below, and half upwards.
But…
• With 90 bars of mostly atmosphere, you
have more than 2 layers!
• You effectively have over 30 layers!
• Try going outside on a hot summer day
with 30 coats on…
• So, you can imagine what the surface
temperatures is like...
Temperature profile of Venus
• From textbook.
• Acid rain clouds
are 40-70 km in
the atmosphere,
and end at a
atmospheric
pressure 0.05
bars.
• This is the
same range you
get clouds on
earth.
Why?!
• Lets go back to the formation of the earth.
• At one point the earth had 250 bars of
water vapor and about 60 bars of carbon
dioxide in its atmosphere.
• Venus would have had the same start.
• The earth made a race against time to
cool the planet with constant attempts to
rain while volcanoes released more and
more gasses into the atmosphere.
So…
• On Earth, the water won. Rains finally
succeeded, and the oceans were formed.
• The Carbon Dioxide dissolved into the
rainwater and ended up in the ocean.
• Venus, however, is a little closer to the
sun.
• So, on Venus, it was just warm enough
that the water did not win.
Also
• The water in Venus’s atmosphere was
also quickly destroyed!
• There are 2 ways to do it.
• 1) UV rays break apart water high up in
the atmosphere to separate the Hydrogen
from the Oxygen and the Hydrogen
escapes.
UV dissociation
No oxygen means no ozone. No ozone means no Stratosphere. With no
Stratosphere, water vapor can go to the top of the atmosphere and UV rays
can penetrate down into the lower atmosphere.
2nd method
• Slow rotation means almost no magnetic
field.
• On the earth, our magnetic field protects
us from Cosmic Rays and the solar wind.
• Without this protection, the highest level of
the atmosphere gets bombarded by the
solar wind.
• The solar wind can destroy water
molecules.
Result:
• The result is a very dry atmosphere which
has a lot of carbon dioxide with no way to
remove the carbon dioxide.
• It could be worse though, all those clouds
and Sulfur Dioxide reflect 75% of the
sunlight. It could actually be hotter on
Venus!
How to look at the surface:
• In any telescope, you will only see clouds!
• So, you need radar to see the surface.
• Several spacecraft have orbited Venus
with radar.
• Altitude: time to take radar to get back
determines altitude!
• So, you can make topographical maps of
the surface of Venus!
Surface map of Venus (from
textbook)
Venus Surface features
• 90% of Venus is very flat (within 1 km).
Flatter than the great plains.
• Lot of volcanoes. About 50k.
• Some are active! However activity is
about 1/5th of Earth’s.
Small and Medium
Collapsed Domes
Large
Volcanoes
Calderas
Lava Flows
Coronae
• Areas of
rising magma
What is missing?
What is missing?
• Craters! There are < 1000 craters on the
surface of Venus.
• Erosion? Nope, no water, and not a lot of wind.
• Lava? Nope, the craters are distributed
randomly – even in regions with flows.
• Atmosphere? The atmosphere destroys any
object < 1 km in diameter (in fact there are many
places where the surface is scorched because of
an explosion within a few km of the surface).
• However, you still expect more.
Solution:
• Somehow, the surface of Venus is < 500
million years old, and maybe as young as
250 million.
• How could this be?
• Not from erosion, there is no plate
tectonics. Lava does not seem to be the
culprit.
Young surface:
• Venus has had a cataclysmic event occur
about 250-500 million years ago.
• Two main possibilities:
• 1) giant impact which melted the surface
• 2) normal Venus cycle (if the Sulfur in the
atmosphere goes away, then the surface
gets hotter, and can melt – recreating the
volcanoes which put back the sulfur and it
unmelts).
Conclusion
• Venus is a very hostile world with a think
atmosphere and extremely hot
temperatures – even at night.
• Venus has a lot of strange surface feature.
Lots of volcanoes, but is very flat!
• The surface of Venus is strangely young.
• This is the, what can go wrong story if a
planet has a run-away greenhouse effect
(porridge is too hot).