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Venus Venus Facts Venus Diameter: 12,104 km, 0.95 Earth Diameters Planetary Mass: 4.86x1024 kg, 0.82 Earth masses Density: 5.24 g/cm3 Avg. Dist. from Sun: 108 million km, 0.7233 AU Closest dist. to Earth: 38 million km Number of moons: 0 Magnetic field: None Average temperature: 460oC on both the day and night sides Atmospheric composition: 96.5% Carbon Dioxide (CO2), 3.5% Nitrogen (N2) Venus Facts – cont. Axial tilt: 177.3o, which means that it is rotating in space upside down! It’s axis is only 2.7o tilted from ecliptic, which isn’t enough to cause seasons. Length of Day: (clockwise) 243 Earth days backwards Length of Year: 225 Earth days Name Origin • Named after the Roman goddess of love and beauty. • The planet was named Venus because it was the brightest of the planets known to the ancients. • Commonly called the “evening star” or the “morning star” • Much brighter than any star. • Originally the Greeks thought Venus was two different planets. Peculiar Rotation • Rotation is retrograde: rotation is opposite of the direction of orbital motion – Orbit motion around the Sun: counterclockwise – Venus’s rotation on its axis: clockwise – Planets and satellites have prograde rotation except Venus, Uranus and Pluto Appearance of Venus • Simple telescopes can detect that Venus goes through phases like the Moon • It can often seen in the eastern sky at dawn or in the western sky after sunset • Surface is always obscured by a very dense cloud cover • Clouds reflect 70% of the sunlight, causing its brightness Enhanced picture of Venus shot through a violet filter by the Galileo spacecraft Phases of Venus • Venus appears to go through phases like the moon • Different from the moon because its distance from us changes drastically Venus Interior • Internal composition is probably similar to Earth. • It is possible that the core is liquid iron. • Core has less mass than Earth’s (only 23% of total planet). • Based on size, Venus should be heavier • We do not know if the core contains less iron or if it is smaller than Earth’s. Interior • The presence of volcanoes suggests a molten interior • Venus has no planet-wide magnetic field, possibly due to the fact that Venus rotates too slowly. • Venus has no plate tectonics, possibly due to that the crust is too hot and soft to move in rigid plates Venus Atmosphere • • • • Atmosphere of mainly CO2 Clouds of sulfuric acid No water Crushing atmospheric pressure of about 90 atm • High-velocity winds in upper atmosphere but low-velocity surface winds (we don’t know why) • High surface temperatures from “Greenhouse Effect” • Slow surface erosion rate • High clouds with a clear CO2 atmosphere below. • Much warmer atmosphere near the planet’s surface than Earth’s, but colder at high altitudes. Greenhouse Effect The sunlight that is able to pass through the clouds warms the surface. The surface then re-radiates heat upwards. The heat becomes trapped below the clouds. The result is a much higher surface temperature than would be present without the blanketing effect of the atmosphere. Carbon dioxide cycle on Earth keeps us from being like Venus But this cycle would not work if there’s no liquid water! Venus Atmospheric Missions • Mariner 10 – Fly-by in 1973 on its way to Mercury • Pioneer Venus – Five probes in 1978 • Vega 1 and 2 – Two probes in 1985 • Galileo – Fly-by in 1990 • Europe’s Venus Express - 2006 • Messenger – Made fly-bys in 2006 and 2007 on its way to Mercury Pioneer Venus 1978 Orbiter Venus Atmosphere Venus Topography Visible versus Radar • Orange colors in radar images are not “real”. • Colors have been enhanced to show surface features more clearly Venus Surface • Surface rocks are basaltic (similar to our ocean floor). • Dense atmosphere prevents studying the surface from orbit. • Craters and “pristine” appearance suggest young surface. • No plate tectonics • No true continents or ocean basins • We do not know the range of ages of the rocks on the surface • We do not know how the surface changed with time Surface • The surface of Venus is surprisingly flat, with only a few major highlands and several large volcanoes • The surface of Venus shows no evidence of plate tectonics (or the motion of large crustal plates) – No long chain of volcanic mountains Venus Surface Features Planitia: Low plains Terra: Extensive land masses Planum: Plateaus Corona: Ovoid-shaped volcanic features Volcanic craters: numerous Impact Craters: about 1000, randomly distributed Volcanic Structures Shield Volcanoes • Low-sloping volcanoes formed from repeated eruptions of low-viscosity lava Sif Mons Shield Volcano Impact Craters Yablochkina impact crater • Radar images from Magellan • Bright regions: high radar reflectivity – “rough” • Dark regions: low reflectivity – “smooth” Addams Impact Crater The radar bright outflow associated with the 90 km crater stretches over 600 km to the east. Lava Channel The channel is about 2 km wide and shows branches and islands along its length. The image shown here is about 50 km wide. Probably low viscosity, high temperature lava. Volcanic “Pancake" Domes • Flattened tops and steep edges. • Probably formed by the eruption of thick lava. • High atmospheric pressure likely caused the flattened tops • The largest dome is 62 km in diameter. “Tick” • Volcanic feature • Dome with a large volcanic vent (caldera) • Surrounded by radial spurs that look like legs. Nova Magellan image of a nova. •A pattern of hills and valleys that radiate outward from a single point. •This nova is about 250 km in diameter Maxwell Montes • The Maxwell Montes are the highest mountains on Venus • rising up to 11 km above the surface. Venus Surface Studies • Mariner 2: First planetary mission in 1972 • Pioneer Venus: Topography and atmospheric probes in 1978 • Veneras 8 – 14: Surface landers from 1975-1982 • Veneras 15 & 16: Orbital radars, 1984 • Magellan: Orbital radar images, topography and gravity data, 1990-1994 • Europe’s Venus Express: 2006 Venus Surface Studies Orbital Missions: Pioneer Venus, Magellan. Surface Missions: Vega and Venera Future studies: • NASA and the ESA are looking into the possibility of sending a lander to Venus to collect rock samples and return them to Earth for analysis • New generation of surface measurements by landed spacecraft. • Still in the proposal stage Proposed Venus Sample Return mission 6 years round trip Venera Lander Images of Venus Venera 9 1975 53 min. surface operation Venera 13 1982 2 hrs 7 min. surface operation Venera 10 1975 65 min. surface operation Venera 14 1982 60 min. surface operation Magellan 1989-1994 The primary objective of the mission was to map the surface the surface features of Venus 98% of the surface was imaged at high resolutions Magellan Volcanic "pancake" domes in Tinatin Planitia, Venus Computer generated 3-dimensional perspective view of the "crater farm" At 280 km diameter, Mead Crater is the largest impact crater on Venus. 3-dimensional image of Sapas Mons a 1.5 km high volcano Top Ten Questions about Venus 1. Was Venus ever a habitable planet? 2. Did Venus possess abundant surface water in its early history? 3. What is the nature of weathering on the Venusian surface? 4. What has been the composition and evolutionary history of the Venusian atmosphere? 5. What has been the volcanic history of Venus over time? 6. Did Venus ever have plate tectonics? 7. What has been the cratering rate on Venus over time? 8. What are the ages of different rocks and features on Venus’ surface? 9. What is the overall chemical composition of Venus and how does it compare to other planetary bodies in the solar system? 10. What are the geophysical properties (heat flow, seismic activity, etc.) of the interior and what do they reveal about the internal structure of Venus?