Venus Earth s Sister Planet

Transcription

1 Venus Earth s Sister Planet Orbital Properties 3rd brightest object in the sky, after Sun and Moon. Can even be seen in broad daylight Often called the morning star or the evening star, as it is captive to the Sun Orbital Properties Appearance through a telescope Goes through phases like the Moon Completely covered by clouds Surface? Can t see it. 3 1

2 9.1 Orbital Properties Phase and apparent brightness of Venus depends on distance from Earth and position relative to the Sun Physical Properties Properties of Earth and Venus Basic Properties: note similarities vs. differences Physical Properties Venus rotates slower than any other planet. Plus, it rotates backwards ( retrograde ) compared to its orbital direction. 6 2

3 9.2 Physical Properties Slow retrograde rotation of Venus causes big difference between solar day and sidereal day Solar = 117 Earth days Sidereal = 243 Earth days The sidereal day is actually longer than a year on Venus Long-Distance Observations of Venus Through Earth-based telescopes, Venus s dense atmosphere and thick clouds make surface impossible to see Surface temperature is about 850 F (730 K) hotter than Mercury! Long-Distance Observations of Venus Even probes flying near Venus, using ultraviolet or infrared, can see only a little deeper into the clouds 9 3

4 Spacecraft Exploration of Venus US: Mariner 2 in 1962 (first to visit) US: Mariner 5: 1967 US: Pioneer Venus: (orbiter/radar + probes) US: Magellan (orbiter/radar) ESA: Venus Express (orbiter) Russia: Venera Russia s Venera missions to Venus Venera 1 - Venus Flyby (Contact Lost) Venera 2 - Venus Flyby (System Failed) Venera 3 - Venus Lander (Contact Lost) Venera 4 - Venus Probe Venera 5 - Venus Probe Venera 6 - Venus Probe Venera 7 - Venus Lander Venera 8 - Venus Lander Venera 9 - Venus Orbiter/Lander (1975) Venera 10 - Venus Orbiter/Lander (1975) Venera 11 - Venus Lander (1978) Venera 12 - Venus Lander (1978) Venera 13 - Venus Lander (1981) Venera 14 - Venus Lander (1981) Venera 15 - Venus Orbiter (1983) Venera 16 - Venus Orbiter (1983) 11 Surface: Relatively smooth 75% covered with lowland lava plains Similar in origin to lunar maria 12 4

5 No evidence of plate tectonics Mountains, a few craters, many volcanoes and large lava flows 13 Continents Aphrodite Terra (size of Africa) Ishtar Terra (size of Australia) Ishtar Terra 14 Craters Shield volcanoes Pancake domes Coronae 15 5

6 9.2 Geology of Venus Craters 16 Craters Low # indicates a young age Maybe only 500 to 600 million years Most craters are large, km diameter Why? Smaller meteorites burned up in atmosphere Craters are frequently distorted Projectile must have broken up in atmosphere and exploded Created multiple craters in some cases 17 Ridges Intersecting ridges indicate repeated compression and buckling of the surface. The dark areas represent regions that have been flooded by lava upwelling from cracks like those shown in the next slide. 6

7 Lava flows These cracks in Venus s surface have allowed lava to reach the surface and flood the surrounding terrain. The dark regions are smooth lava flows. The network of fissures visible here is about 50 km long. 19 Volcanoes Many different volcanic features seen on surface Largest volcano km (300 mi) across and 3 km (2 mi) high Thousands of smaller volcanoes & other volcanic features Most are shield volcanoes WHAT S THAT? A shield volcano is usually built almost entirely of low viscosity lava flows. They are named for their large size and low profile, resembling a warrior's shield. The lava they erupt builds up the shield volcano's distinctive form. 20 Other Volcanic Features Pancake domes Circular, 25 km across x 2 km high Made by eruptions of very thick lava flowing out evenly 21 7

8 Other Volcanic Features Coronae Not all magma makes it to the surface Stresses under surface cause fractures Raised center, depressed edge Only seen on Venus 22 Tectonic Activity Mantle convection currents Exert forces on crust Pushes and stretches crust Ishtar = most dramatic results of these forces Tibetan plateau and Himalayan mountains similar in origin 23 On Venus Surface Atmospheric pressure = 90x Earth Temp hot enough to melt lead Determined by Venera craft Igneous rocks, primarily basalts Ejecta from impacts, lava flows Surface lit by diffused light - red tint Hot & dry, light winds Conditions always the same, day and night, any latitude 24 8

9 On Venus Surface 25 On Venus Surface 26 On Venus Surface 27 9

10 9.5 The Atmosphere of Venus Composition & Structure 90x more massive than Earth s atmosphere Earth: 90% of atmosphere lies within 10km of sea level Venus: 90% of atmosphere lies at an altitude of 50km above the surface Polar vortices 28 Polar Vortex (south pole) 29/56 Polar Vortices on Earth On the Earth, there are seasonal effects and temperature differences between the continental zones and the oceans that create suitable conditions for the formation and dispersal of polar vortices. On Venus there are no oceans or seasons, and so the polar atmosphere behaves very differently. March /56 10

11 9.5 The Atmosphere of Venus Composition & Structure Venus and Mars atmospheres similar in composition, but not in atmospheric pressure Earth atmospheric pressure at sea level = 1 bar Mars atmospheric pressure = bar Venus atmospheric pressure = 90 bars The Atmosphere of Venus Composition & Structure Sulfur dioxide (SO 2 ) in middle atmosphere Troposphere Thick layer of H 2 SO 4 Combination of SO 2 and H 2 O This is diluted and washed out by abundance of H 2 O in Earth's atmosphere 32 Upper atmos is actually colder than Earth s Temp soars through troposphere, especially below solid cloud bank km above surface

12 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 34 Greenhouse Effect CO 2 = infrared blind, trapping heat near surface Venus and Earth: same amount of CO 2 Earth: Most CO 2 is either dissolved in oceans or in carbonate rocks Carbon dioxide cycle

13 Greenhouse Effect CO 2 = infrared blind, trapping heat near surface Venus and Earth: same amount of CO 2 Earth: Most CO 2 is either dissolved in oceans or in carbonate rocks Carbon dioxide cycle Venus: no oceans, no CO 2 cycle; CO 2 is all in the atmosphere But Venus experienced similar volcanic outgassing during formation as Earth. Where did the water go? 37 Where did the water go? Possibly from slight increase in ultraviolet energy output from the Sun Ultraviolet radiation breaks down water in H and O H escapes into space, O combines chemically with surface rock This resulted in slight increase in atmospheric temp Caused increased evaporation of water/oceans, and Increased production of off-gassing by rocks This in turn increased CO 2 and H 2 O Ultraviolet radiation breaks down water in H and O H escapes into space, O combines chemically with surface rock Vicious circle Runaway Greenhouse Effect 38 Runaway Greenhouse Effect (86ºF) 39 13

14 9.5 The Atmosphere of Venus Surface temperature: 700K (900ºF) Greenhouse effect CO 2 = infrared blind, trapping heat near surface Most CO 2 on Venus was either dissolved in oceans or in rocks Then, Venus increased production of CO 2 Possibly from slight increase in energy output from the Sun This resulted in slight increase in atmospheric temp Caused increased evaporation of water/oceans, and Increased production of off-gassing by rocks The Atmosphere of Venus Surface temperature: 700K (900ºF) Greenhouse effect This in turn increased CO 2 and H 2 O Ultraviolet radiation breaks down water in H and O H escapes into space, O combines chemically with surface rock Vicious circle Runaway Greenhouse Effect The Atmosphere of Venus Earth 42 14

15 9.6 Venus s Magnetic Field and Internal Structure What magnetic field?? Venus has no magnetic field, probably because its rotation is so slow No evidence for plate tectonics, either Venus s Magnetic Field and Internal Structure Internal structure A rocky mantle lies above a metallic core. Temperatures in the interior may be high enough to partially melt the core, but are not high enough to produce convective motions in the core, a magnetic field, or tectonic activity Venus s Magnetic Field and Internal Structure Internal structure 45 15