Astronomy A BEGINNER’S GUIDE TO THE UNIVERSE EIGHTH EDITION CHAPTER The Terrestrial Planets Lecture Presentation © 2017 Pearson Education, Inc Chapter The Terrestrial Planets © 2017 Pearson Education, Inc Units of Chapter • • • • • • • • • Orbital and Physical Properties Rotation Rates Atmospheres The Surface of Mercury The Surface of Venus The Surface of Mars Internal Structure and Geological History Atmospheric Evolution on Earth, Venus, and Mars Summary of Chapter © 2017 Pearson Education, Inc 6.1 Orbital and Physical Properties • The orbits of Venus and Mercury show that these planets never appear far from the Sun © 2017 Pearson Education, Inc 6.1 Orbital and Physical Properties • The terrestrial planets have similar densities and roughly similar sizes, but their rotation periods, surface temperatures, and atmospheric pressures vary widely © 2017 Pearson Education, Inc 6.2 Rotation Rates • Mercury can be difficult to image from Earth, rotation rates can be measured by radar © 2017 Pearson Education, Inc 6.2 Rotation Rates • Mercury was long thought to be tidally locked to the Sun; measurements in 1965 showed this to be false • Rather, Mercury’s day and year are in a 3:2 resonance; Mercury rotates three times while going around the Sun twice © 2017 Pearson Education, Inc 6.2 Rotation Rates Venus © 2017 Pearson Education, Inc Mars 6.2 Rotation Rates • All the planets rotate in a prograde direction, except Venus, which is retrograde © 2017 Pearson Education, Inc 6.3 Atmospheres • Mercury has no detectable atmosphere; it is too hot, too small, and too close to the Sun • Venus has an extremely dense atmosphere The outer clouds are similar in temperature to Earth, and it was once thought that Venus was a “jungle” planet We now know that its surface is hotter than Mercury’s; hot enough to melt lead • The atmosphere of Mars is similar to Earth in composition, but very thin © 2017 Pearson Education, Inc 6.6 The Surface of Mars • There is no evidence of a connected river system The features are probably due to flash floods © 2017 Pearson Education, Inc 6.6 The Surface of Mars • This feature may be an ancient river delta Or, it may be something entirely different © 2017 Pearson Education, Inc 6.6 The Surface of Mars • Much of the northern hemisphere may have been ocean © 2017 Pearson Education, Inc 6.6 The Surface of Mars • • • Impact craters less than km across have mostly been eroded away Analysis of craters allows estimation of the age of the surface Crater on right shows ejecta that may have been liquified by the impact that created the crater © 2017 Pearson Education, Inc 6.6 The Surface of Mars • Recently, gullies have been seen that probably indicate the occasional presence of liquid water © 2017 Pearson Education, Inc 6.6 The Surface of Mars Viking photo Mars rover Curiosity near Mt Sharp in Gale Crater © 2017 Pearson Education, Inc 6.6 The Surface of Mars • Landscape near the north polar cap by the Phoenix lander © 2017 Pearson Education, Inc 6.7 Internal Structure and Geological History • Internal structure of Mercury, Mars, and the Moon, compared to Earth © 2017 Pearson Education, Inc 6.8 Atmospheric Evolution on Earth, Venus, and Mars • At formation, planets had primary atmosphere—hydrogen, helium, methane, ammonia, water vapor—which was quickly lost • Secondary atmosphere—water vapor, carbon dioxide, sulfur dioxide, nitrogen—comes from volcanic activity • Earth now has a tertiary atmosphere, 20 percent oxygen, due to the presence of life © 2017 Pearson Education, Inc 6.8 Atmospheric Evolution on Earth, Venus, and Mars • Earth has a small greenhouse effect; it is in equilibrium with a comfortable (for us) surface temperature © 2017 Pearson Education, Inc 6.8 Atmospheric Evolution on Earth, Venus, and Mars • Venus’s atmosphere is much denser and thicker; a runaway greenhouse effect has resulted in its present surface temperature of 730 K © 2017 Pearson Education, Inc Summary of Chapter • • Mercury is tidally locked in a 3:2 ratio with the Sun Mercury has no atmosphere, Venus has a very dense atmosphere, and the atmosphere of Mars is similar to Earth in composition but very thin • Mercury has no maria, but does have extensive intercrater plains and scarps © 2017 Pearson Education, Inc Summary of Chapter 6, cont • Venus is never too far from the Sun and is the brightest object in the sky (after the Sun and Moon) • • • It has many lava domes and shield volcanoes Venus is comparable to Earth in mass and radius Large amounts of carbon dioxide in its atmosphere and closeness to the Sun led to a runaway greenhouse effect and very hot surface © 2017 Pearson Education, Inc Summary of Chapter 6, cont • • • • • Northern and southern hemispheres of Mars are very different South is higher and heavily cratered North is lower and relatively flat Major features include the Tharsis bulge, Olympus Mons, Valles Marineris There is strong evidence for water on Mars in the past © 2017 Pearson Education, Inc Summary of Chapter 6, cont • • • Mercury has very weak remnant magnetic field Venus has none, probably because of very slow rotation Neither Venus nor Mars show signs of substantial tectonic activity © 2017 Pearson Education, Inc ... eroded away Analysis of craters allows estimation of the age of the surface Crater on right shows ejecta that may have been liquified by the impact that created the crater © 2017 Pearson Education,... This map of the surface features of Venus is on the same scale as the Earth map below it © 2017 Pearson Education, Inc 6.5 The Surface of Venus • Venus as a globe, imaged by Magellan © 2017 Pearson... rolling volcanic terrain Southern hemisphere (bottom) is heavily cratered highlands; average altitude is km above the northern • Assumption is that the northern surface is younger than the southern