Download Atmospheres of Terrestrial Planets: Structure and Greenhouse Effect in ASTR 105G - Prof. J and more Study notes Astronomy in PDF only on Docsity! Lecture 20 Atmospheres of Terrestrial Planets ASTR 105G: The Planets April 7, 2009 Announcements 1. HOMEWORK 9 DUE Thursday 2. Exam next Tuesday (Chapter 5.3 - Chapter 9) 3. Review session Monday night, 7pm 4. Today’s stuff will not be on this exam. It will be on the final exam. 5. Last week’s quiz Last time ... • We compared the geological features of the inner planets • Went over in detail the characteristics of Earth’s features and how they are formed 1 Atmospheric Science 1.1 Basic Concepts Motivation Refer to Figure 1 for planet comparisons of atmospheres. Importance of Atmospheres for Planets • A layer of thin gas that surrounds a planet, moon, etc. • Typically cool enough to contain molecules (O2, H2O, CO2) • Create pressure due to the motion of molecules - decreases with altitude • Pressure determines how water exists (solid, liquid, or gas) - very important • Atmospheres absorb, scatter, reflect light → temperature • Give climate and weather • Heat a planet by the greenhouse effect Lecture 20 April 7, 2009 2 / 6 Figure 1: Comparison of terrestrial atmospheres. Lecture 20 April 7, 2009 5 / 6 Figure 3: The layers of the atmosphere of the Earth. Planets with atmospheres may have similar stratification. Note the temperature profile with altitude. Lecture 20 April 7, 2009 6 / 6 Thermosphere • The topmost layer with any appreciable density • The gases here absorb x-rays since these are the first gases the x-rays see • This heating can be quite effective3 • Like a hot oven • The thermosphere also gets partially ionized by x-rays and this is where the aurora can exist - in the ionosphere Exosphere • Very high up - 1000 km4 • Very low density Magnetosphere • The solar wind is a steady stream of charged particles from the Sun • Objects with no magnetic field are penetrated by these particles (Venus, Mars, Mercury, Moon) • Objects with strong enough magnetic fields divert the particles5 • Some get in near the poles and spiral along the field lines • See Figure 10.11 • Aurora6 • See how special we are? Basic Atmospheric Structure of Inner Planets • Forget the Moon and Mercury • Earth, Venus, and Mars have a troposphere • All 3 have a warm thermosphere • Earth is only one with a stratosphere because of ozone For next time ... 1. We will talk about weather on the individual terrestrial planets 3http://www.ambrosevideo.com/resources/documents/AtmosphereTemperatureGradiant.jpg 4http://upload.wikimedia.org/wikipedia/commons/7/78/Earth Atmosphere.svg 5http://upload.wikimedia.org/wikipedia/commons/f/f3/Magnetosphere rendition.jpg 6http://www.knowledgerush.com/wiki image/e/e7/Earth’s atmosphere.jpg
