Chapter 9: Atmospheres of the Terrestrial Planets
Feb 22, 2016
Chapter 9:Atmospheres
of the Terrestrial Planets
Terrestrial Atmospheres
Only Earth, Venus and Mars have a substantial atmosphere. The Moon and Mercury only have traces of
gases around them.
The primary atmosphere was mostly H and He
H and He were captured during formation. Since all the terrestrial worlds have small masses, their gravity wasn’t strong enough to hold on to these gases and they escaped to space. Only massive planets like Jupiter can hold on to a primary atmosphere.
Venus, Earth and Mars are on their 2nd atmosphere after having
lost their first one
Play with Gas Retention Simulator on ClassAction website in Resources Menu
Most secondary atmospheres come from volcanoes and
comets
The gases are mostly carbon dioxide, carbon monoxide, sulfur dioxide, water vapor and nitrogen
The Greenhouse Effect is important on Venus, Earth and Mars
A balance is established between the incoming energy and the outgoing energy. Since blackbody radiation depends on temperature, the balance point depends on the temperature of the planet
On Venus a runaway greenhouse effect baked the planet. The
balance point is almost 750 KThe clouds of Venus give it a very high albedo (0.65). It’s temperature would be below freezing if not for the greenhouse effect. The thick atmosphere of CO2 causes an extreme greenhouse effect.
The atmosphere of Mars is too thin to have much
of a greenhouse
effectLike Venus, it’s mostly CO2 but it’s so thin there just isn’t much gas to absorb infrared radiation from the ground
Earth’s atmosphere managed to lock away almost all the CO2
If all the CO2 locked up in Earths’ rocks were released, Earths’ atmosphere would be 98% CO2. As it is, CO2 Earths’ atmosphere
makes up less than 0.04% of
How did our atmosphere get this way?
Most of the CO2, CO and SO2 got locked up by the oceans as rocks like limestone. That left mostly
nitrogen and smaller amounts of CO2. Life created the oxygen.
Earth’s Atmosphere is layered
like an onion
The layers are due to how the temperature changes with altitude. Mars and Venus don’t show the same kind of layering.
The way temperature changes is due to energy
transport
In the troposphere convection is driven by heat from the ground so the temperature decreases with altitude
In the stratosphere and thermosphere energy is absorbed directly from the Sun so the temperature increases with altitude
Beyond the atmosphere, Earth has a
MagnetosphereThe magnetosphere shields the Earth’s atmosphere from the solar wind.
When particles trapped in the magnetic field collide with the
upper atmosphere we get auroras
The weak or non-existent magnetic fields of Venus and Mars lead to strong erosion by the solar
winds
The stronger gravity of Venus has been able to hold on to its atmosphere but Mars lost most of its
atmosphere to erosion by the solar wind.
Just as in the interior of the planets, convection is
important to atmospheres
Rotation and the Coriolis effect are also important
Convection in the upper atmosphere is influenced by the
Coriolis Effect
Winds in the upper atmosphere of Venus also show
strong convection
Despite its thin atmosphere, convection on Mars is
important to its global winds
Convection is also important on a smaller
scale
Thunderstorms are driven by convection
Static electricity developed by the convection creates lightning
Mars also shows convection in its clouds and storms
Martian Global Dust Storm
Dust Storm Erupting out of North Pole of Mars
Dust Devils are small scale convection
Dust devils on Mars can be several kilometers tall
Dust devils are found in dry places on Earth
Weather on
Venus?
The ESA’s Venus Express is now taking a close look at the atmosphere of Venus
Is mankind changing Earth’s atmosphere?
Man?
Each spring in Antarctica a hole develops in the ozone
layer
The Ozone Hole changes from year to year
Ozone depletion is caused by CFC’s
CFC’s are Chlorofluorocarbon molecules which are man made compounds. They do not occur naturally
The solution: stop using CFC’s
The 1987 Montreal Treaty gradually reduces the production and consumption of CFC’s worldwide
Is the Ozone Hole getting worse or better?
Our actions have led to an increase in the level of a number of greenhouse
gasesUnfortunately, we can’t stop producing these gases as easily as we stopped producing CFC’s
Deforestation removes the trees that remove CO2
The cut trees are usually burned which adds more CO2 to the atmosphere
There is a direct relationship between the level of CO2 and
the global average temperature
Our actions may be keeping us from another ice age
All climate models predict that it will get warmer
We are performing an experiment on our atmosphere.
What the outcome will be we don’t yet know