Announcements
•The last Dark Sky Observing Night is
Monday night (11/9). Starts at 7:30pm at
the APSU Observatory on “The Farm”.
Try to arrive a little early so your lights
don’t interfere with the observing in
progress. This is the last chance to go to
a Dark Sky Night so don’t miss it.
Chapter 9:
Atmospheres
of the
Terrestrial
Planets
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 hydrogen and helium
The original atmosphere of the terrestrial worlds
would have been much like Jupiter and Saturn. With
their low mass, though, the terrestrial worlds quickly
lost their hydrogen and helium to space.
Venus and Mars
nd
are on their 2
atmosphere
after having lost
their first one
The Earth is on its
3rd atmosphere!
Play with Gas Retention
Simulator on ClassAction
website in Downloads menu.
Select “All Simulations”.
Secondary atmospheres come
from volcanoes and comets
The gases are mostly
carbon dioxide, carbon
monoxide, sulfur dioxide,
water vapor and nitrogen
Earth’s
atmosphere
is much
different
than Mars or
Venus
Earth’s atmosphere lacks
large amounts of CO2.
Carbon dioxide makes up
less than 0.04% of Earths’
atmosphere
Most of Earth’s CO2 got
trapped in the oceans
Minerals and salts in the
oceans reacted with the
CO2 to form limestone
iClicker Questions
ClassAction website
Terrestrial Planets module
Earth’s Early Atmosphere
several options
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 Earth, the Greenhouse
Effect keeps us from being
an ice world
On Venus a runaway greenhouse
effect baked the planet. The
balance point is almost 750 K
The clouds of Venus
give it a very high
albedo (0.65). It’s
temperature would be
much cooler 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
effect
Like Venus, it’s mostly
CO2 but it’s so thin
there just isn’t much
gas to absorb infrared
radiation from the
ground
Homework Assignment
Do The Greenhouse Effect from
Lecture-Tutorials for Introductory
Astronomy. Pages 105 - 110
Complete it for Monday, we will
go over it in class.
How did our
atmosphere
get this
way?
Life plays a major role in our
tertiary atmosphere
Earth’s current
atmosphere is
78% nitrogen
and 21% oxygen
with only traces
of CO2
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. The oxygen comes from life.
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
In the stratosphere and
thermosphere energy is
absorbed directly from the sun