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Chapter 9 Venus © 2014 Pearson Education, Inc. 9.1 Orbital Properties • Venus is much brighter than Mercury, and can be farther from the Sun • Called morning or evening star, as it is still “tied” to Sun • Brightest object in the sky, after Sun and Moon © 2014 Pearson Education, Inc. 9.1 Orbital Properties Apparent brightness of Venus varies, due to changes in phase and distance from Earth Venus appears brightest when it is about 39o from the Sun © 2014 Pearson Education, Inc. 9.2 Physical Properties • Radius: 6000 km (.95 x Earth) • Mass: 4.9 x 1024 kg • Density: 5200 kg/m3 (5.2 g/cm3) • Rotation period: 243 days, retrograde (CW rotation) • Atmosphere is 90x Earth’s (14.92 psi x 90 = 1342.8 psi). • Composition and layering is similar to Earth’s © 2014 Pearson Education, Inc. 9.2 Physical Properties Slow, retrograde rotation of Venus results in large difference between solar day (117 Earth days) and sidereal day (243 Earth days); note that the solar day is a large fraction of the year, and the sidereal day is even longer than the year (225 Earth days). © 2014 Pearson Education, Inc. 9.3 Long-Distance Observations of Venus Dense atmosphere and thick clouds make surface impossible to see Surface temperature is about 730 K—hotter than Mercury! © 2014 Pearson Education, Inc. 9.3 Long-Distance Observations of Venus Even probes flying near Venus, using ultraviolet or infrared, can see only a little deeper into the clouds Longer infrared wavelength allows us to “see” deeper into Venus’s lower clouds © 2014 Pearson Education, Inc. 9.4 The Surface of Venus Surface is relatively smooth Two continent-like features: Ishtar Terra and Aphrodite Terra No large scale plate tectonics Mountains, a few craters, many volcanoes and large lava flows © 2014 Pearson Education, Inc. 9.4 The Surface of Venus Surface mosaics of Venus (Ishtar Terra is upper left, Aphrodite is lower right) © 2014 Pearson Education, Inc. 9.4 The Surface of Venus Surface maps of Venus, with Earth comparison Elevated areas - 8% of Venus, 25% of Earth © 2014 Pearson Education, Inc. 9.4 The Surface of Venus Ishtar Terra is one of two continent-sized features on the surface of Venus. Maxwell Montes mountain range is 14 km above lowest elevation. (Mt. Everest is 20 km above deepest trench) Right: Cleopatra impact crater with center lava flow and double-ringed structure indicating an impact crater © 2014 Pearson Education, Inc. 9.4 The Surface of Venus The other is Aphrodite Terra The intersecting ridge indicate repeated compression and buckling of the surface. Dark areas are extensive lava flows. © 2014 Pearson Education, Inc. 9.4 The Surface of Venus Lava has flowed from cracks or fissures on the surface (these are 50 km long). Upwelling magma flowed, solidified, then material withdrew from below, and surface collapsed. Some rilles (lava channels) are long and have deltas. © 2014 Pearson Education, Inc. 9.4 The Surface of Venus Volcanoes on Venus; most are shield volcanoes. (Sif Mons (left), and Gula Mons (right)) Similar to the Hawaiian Islands (basalt), but are distributed randomly – unlike Earth’s volcanoes located at plate boundaries. They are big because there is no movement of plates over an active vent. © 2014 Pearson Education, Inc. 9.4 The Surface of Venus Other volcanic features include lava domes (pancake domes 25 km across) and coronas. Coronae are unique to Venus. They are caused by upwelling mantle material (300 km across). Evidence that volcanism is still going on include: CO2 levels fluctuate, bursts of radio energy (lightning from volcanism). No “smoking gun” or erupting volcano has been seen. © 2014 Pearson Education, Inc. 9.4 The Surface of Venus Impact craters on Venus, the largest named after Margaret Mead (Mead Crater - 280 km). Erosional agents include volcanism and a little from the atmosphere. Much of the planet resurfaces every 500 my. Young crust – less than 1 BY, some 200 to 300 my old. © 2014 Pearson Education, Inc. 9.5 The Atmosphere of Venus Venus’s atmosphere is very dense Solid cloud bank 50–70 km above surface Atmosphere is mostly carbon dioxide; clouds are sulfuric acid © 2014 Pearson Education, Inc. 9.5 The Atmosphere of Venus Upper atmosphere of Venus has high winds, but atmosphere near surface is almost calm © 2014 Pearson Education, Inc. 9.5 The Atmosphere of Venus Venus is the victim of a runaway greenhouse effect—just kept getting hotter and hotter as infrared radiation was reabsorbed © 2014 Pearson Education, Inc. 9.6 Venus’s Magnetic Field and Internal Structure No magnetic field, probably because rotation is so slow No evidence for plate tectonics Venus resembles a young Earth (1 billion years)—no asthenosphere, thin crust © 2014 Pearson Education, Inc.