Venus Orbit, Rotation Atmosphere (Greenhouse effect) Surface Features Interior Mariner 10 image Venus (The most visited planet) Mariner 2 (1962) Mariner 5 (1967) Mariner 10 (1974) Poineer Venus (1978) (Orbited 150 km above the Venus and dispatched a multiprobe.) Venera 4 through Venera 12 (1967-1978) Venera 7 (1970) --- successful (survived for 23 min) Venera 15 and 16 (1983) Magellan (1990-1994) (Mapped 98 % of the surface) 1
Physical properties Radius: 6052 km (0.95 Earth radii) Mass: 4.9 x 10 24 kg (0.82 the mass of Earth) Average density: 5200 kg/m 3 Surface gravity: 0.91 times that of Earth Distance from the Sun 0.72 AU Venus is often called Earth s sister planet. Moons: 0 Magnetic field: none (no evidence for liquid core) Sidereal orbital period: 225 days Synodic orbital period: 584 days Sidereal rotation period: 243 days Venus rotates backwards retrograde spin sun rises in the west and sets in the east Inferior Planets (Venus, Mercury) Greatest Eastern Elongation Maximum brightness (crescent) after 36 days Superior Conjunction Sun 39 Inferior Conjunction Earth Greatest Western Elongation Greatest Elongation: Venus - 47, Mercury - 28 2
Rotations of Planets Inclinations Mercury: 0, Venus: 177, of axis Earth: 23 ½, Mars: 24 Why is Venus rotating backward, and why so slowly? planet was struck by a large body. Interesting & strange coincidence: Nearly perfect 5:1 resonance Hence Venus always presents nearly the same face to Earth at closest approach. 3
Atmospheric Structure of Venus jet streams 300-400 km/h from west to east. (fastest at the equator) At surface, ~ 100 times the pressure of Earth s atmosphere. Pressure at 50 km is close to that at Earth s surface. (90% of atmosphere on Earth lie within 10 km though on Venus 90% level is found at 50 km) Temperature ~ 730 k High temperature, high pressure, sulfuric acid: a Hell of a place to live Atmospheric Composition CO 2 96% (dominant), N 2 4%, trace molecules: H 2 O (water), SO 2 (sulfur dioxide), CO (carbon monoxide), argon Most clouds are at 50 km sulfuric acid! (70% of the sunlight get reflected by the clouds) 4
The Greenhouse Effect 30% of the Sun s visible light penetrates the clouds This gets absorbed by Venus s surface and re-radiated in the IR (infrared) The IR radiation is trapped by CO 2, which heats up the planet. A balance is reached between incoming and outgoing radiation at a temperature of about 700 Why didn t the Earth develop like this? -temperature was cool enough for liquid H 2 O -CO 2 dissolved into the oceans and condensed into rock (limestone) On Venus, the runaway greenhouse effect caused all the planet s greenhouse gases carbon dioxide and water vapor to end up in the atmosphere. Surface Features Ishtar terra Aphrodite terra The elevated continents occupy only 8% of total surface area. On Earth - continents cover 25 % The remainder of Venus s surface is classified as lowlands (27 %) or rolling plains (65 %). 5
Lakshmi Planum (1500 km across) Map of Surface Maxwell montes (14 Km high) Red, yellow high elevations Green, blue rolling hills, lowlands Ishtar Terra 100 km Lakshmi Planum Cleopatra - meteor crater 6
Aphrodite Terra Ovda Regio (compression and buckling) Lada Terra (extends ~ 200 km) Lava channels or lava rivers Venus (600 km Channel) 7
Volcanism and Cratering Lava Domes Venus (Volcanic Pancakes ) 25 km 8
Venus (Maat Mons) 14 km Venus (Volcanic Corona) 9
Venusian Surface (Venera 13 - March 1982) Venus Surface Lightly cratered - Craters are young and fresh Atmosphere protects surface from small impacts Craters show extensive ejecta fields 80% of surface is basaltic lowlands Two continents - Aphrodite Terra & Ishtar Terra Associated with volcanic hotspots No indications of plate tectonics as on Earth Very extensive surface volcanism More than 2,000 volcanic land forms identified by Magellan Coronae, pancake domes, lava flow fields, sinuous lava channels, steep sided domes, etc More than 140 shield volcanoes larger than 100 km in diameter Surface is about 500 million years old Much younger than moon and a bit older than Earth surface 10
Venus Interior Core is probably solid no magnetic field Is there still volcanic activity? not sure 11