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 are on their 2nd

atmosphere after having

lost their first one

Play with Gas Retention Simulator on ClassAction website in Downloads menu. Select “All Simulations”.

The Earth is on its 3rd atmosphere!

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 QuestionsClassAction website

Terrestrial Planets moduleEarth’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

effectLike 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

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 current atmosphere is 78% nitrogen and 21% oxygen with only traces of CO2

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