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 2 nd 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 3 rd 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 CO 2. Carbon dioxide makes up less than 0.04% of Earths’ atmosphere

Most of Earth’s CO 2 got trapped in the oceans Minerals and salts in the oceans reacted with the CO 2 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 CO 2 causes an extreme greenhouse effect.

The atmosphere of Mars is too thin to have much of a greenhouse effect Like Venus, it’s mostly CO 2 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 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 CO 2, CO and SO 2 got locked up by the oceans as rocks like limestone. That left mostly nitrogen and smaller amounts of CO 2. The oxygen comes from life. Earth’s current atmosphere is 78% nitrogen and 21% oxygen with only traces of CO 2

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