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Venus

Venus. Jewel of the Sky Earth’s Sister Planet. General Information. Named after the Roman goddess of love and beauty Once thought to be two different celestial bodies Thus known as the morning or evening star The sun rises in the west and sets in the east

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Venus

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  1. Venus Jewel of the Sky Earth’s Sister Planet

  2. General Information • Named after the Roman goddess of love and beauty • Once thought to be two different celestial bodies • Thus known as the morning or evening star • The sun rises in the west and sets in the east • Slow retrograde motion causes this phenomenon • Slow rotation makes a Venusian day longer than a Venusian year • Features on Venus are named after goddesses of mythology, famous women, and common female first names • Atmosphere • Thick, dense cloud cover • Atmospheric pressure 92 times that of Earth at sea-level (equal to being ~1km beneath the ocean) • Clouds composed of CO2, H2O, and sulfuric acid droplets • Runaway greenhouse effect • Visible to naked eye • Always appears close to the Sun

  3. Planetary Statistics • Mean distance from Sun 108,200,000km • 0.723 A.U. • Orbital Period = 224.7 days • Rotational Period = 243 days • Axis Tilt = 177.4 degrees (23.5) • Diameter = 12,104km (12,756km) • Mass = 4.869 x 1024 (5.97 x 1024) • (.815 of Earth) • Density = 5.25gm/cm3 (5.515gm/cm3)

  4. Stats cont’d • Equatorial surface gravity = 8.87m/sec2 (9.78m/sec2) • Visual albedo = 0.65 (.37) • Moons = none • Surface = Rolling plains, lava flows and very little topographic relief • Atmospheric composition • CO2 96% • Nitrogen 3% • Sulfur dioxide, water vapor,carbon monoxide, argon, helium, neon,hydrogen chloride, and hydrogen fluoride • Mean surface temperature = 170C (330F) • Max temp = 482C (896F)

  5. Atmosphere • It is thickness not density that hides surface • Expected composition formed by secondary processes of differentiation and outgassing • Some fluids may have been supplied to inner planets via cometary collisions • Venus too hot = water vapor • Earth cooler = water fluids • Cloud cover extends >50km • Main cloud deck betwn/25 & 75km • Level @ which H2SO4 (sulfuric acid) can condense • Potent acid rain doesn’t reach the surface (virga) because of evaporation ~30km altitude • Greenhouse Effect • Surface receives less solar radiation than Earth’s • Gas and fluid molecules in atmosphere absorb energy • Cloud cover traps heat from escaping • Heat distributed planet-wide (no cold polar regions) • Mass of water 100,000 times less than Earth’s

  6. Atmosphere (cont’d) • Carbon cycle • Fossilized atmosphere trapped in Earth’s carbonate sedimentary rocks • If released the two planets atmos. would be much more similar • If carbonate rx existed on Venus temp’s now too hot – gas released back into atmosphere • Weathering • Varies with elevation (pressure and temperature zones) • Consistent boundary elevation • Varies by <100m over 100’s of km • Cuts across various types of terrain • Low temp & hi elev. basalt reacts w/sulfur to form pyrite • Bright signatures • Hi elev & lo albedo = young lavas not weathered into pyrite

  7. Venus Atmospheric Profile • The first Soviet probe, Venera 4, descended by parachute through the atmosphere • Apparently was crushed by the dense atmosphere (~90 atm) and high temperatures • Did return information confirming that CO2 makes up about 97% of all gases present (very little water) • Detected droplets of sulphuric acid in the outer cloud deck • Venera data (refined by later Pioneer data) also lead to a general profile of temperature and pressure distributions in the atmosphere (at right)

  8. Venus – Geologic Activity • Venus has a silicate (rocky) crust and mantle with a metallic core • No detectable magnetic field • Slow rotation does not preclude existence of a partial liquid core • Volcanism, weathering, aeolian transport tensional and compressional tectonic forces are dominant geologic processes • No water so weathering and erosion are very different from Earth • Greenhouse may have been process responsible for loss of primal water • Accretion, internal differentiation and out-gassing were important early events

  9. Geologic Activity (cont’d) • Juvenile water • Water as a component of mantle • Small fraction lowers melting temps by ~200K (-100F) • Increases fluidization and formation of an asthenosphere • Mantle processes • No water, no asthenosphere, no plate tectonics • No water, no granite, no continents

  10. Major Geologic Provinces • Lowlands • Cover ~60% of the planet • Rolling plains w/little local relief (<500m) • No evidence for formation by large impacts • Extensive basaltic flows w/few volcanoes • Exhibit compressional tectonic features (ridges, folds and faults) • Few impact craters so probably <1by old • Atalanta Planitia – largest area • Uplands • Isolated domes and broad swells (0-2km elev.) • Extensional tectonics resulting in broad domes capped by fault-bounded rifts systems and some shield volcanoes • Coronae • Volcanic and tectonic • Concentric horst and graben features • Some flow features • Beta Regio – largest upland region

  11. Major Geologic Provinces • Highlands • Continental like • 3-5km elev. • <15% areal extent of planet • Compressional folds, ridges and troughs • Lateral movement of crust • Perhaps different composition • Never been sampled • Aphrodite Terra – largest area >9500km east to west

  12. Magellan • In clean room at JPL • Primary instrument - multimode Radar Mapper (2.385 Ghz, or 12.6 cm wavelength) • SAR imaging mode (18° and 50° off-nadir), res = 360 m and 120 m (1181-394 ft) • It first established orbit on August 10, 1990 after 1 1/2 loops around the Sun • Altimeter mode achieved vertical accuracy < 50 m (164 ft) within a ground cell of 10 km (6.2 mi) diam. • Radiometer mode could sense surface radio-emission, whose signals can be converted to brightness temperatures with an absolute accuracy of ±20° K

  13. Venus Topography

  14. Venus – Geologic Activity • Relatively young surface - ~complete resurfacing about 300-500mya • Small population of craters • Extensive lava flows • Evidence of crustal movement (vertical & lateral) • Topography • Vast plains/lava flows • Highlands deformed by geologic activity (isostatic or compressional forces) • Craters • Distributed randomly across surface • Few by Lunar and Mercury standards • <2km diameters virtually non-existent • Exceptions • When large meteorites break up just before impact • Secondary impacts propelled from primary impact event • Tend to produce linear crater chains

  15. Geologic Activity (cont’d) • Volcanism - >85% of surface is covered by volcanic rock • Very numerous – • >100,000 small shield volcanoes • 100’s of larger features • Lava flows • Long sinuous channels • Some > 7,000km long • Flooded lowlands creating vast plains • Shield volcanoes • Found on all terrain types except tessera • Mostly associated w/rifting (African Rift Valley) • Largest volcanoes >1000km across isolated • Smaller on flanks and in clusters • Calderas • Summit vents • Single and multiple • Larger than any similar features on Earth

  16. Venus Visible vs Radar • Two different perspectives of Venus • Left is a mosaic of images acquired by the Mariner 10 spacecraft • Thick cloud coverage that prevents optical observation of the planet's surface • Surface remained hidden until 1978 • Pioneer Venus 1 spacecraft arrived • The spacecraft used radar to map the surface • The right image show a rendering of Venus from the Pioneer Venus and Magellan radar images

  17. Venus Interior • What is known about the Venusian interior comes primarily from the Venera, Pioneer Venus and Magellan spacecraft • Before thought Venus would have tectonic processes similar to that of Earth's mantle convection • Venus showed no sign of plate tectonism & appears to have a single plate • Differentiated with a basaltic crust extracted from the mantle • Crust appears to be ~25 to 40 kms and in some areas more than 50 to 60 kms • Recent volcanism suggests still retains a partially molten core

  18. Venus Interior • Venus’ slow rate of rotation precludes generation of a magnetic field like the Earth’s • Atmospheric composition that expected by outgassing • Crustal features expression of deep internal mantle convection • Mostly vertical components • No evidence of lateral or plate tectonics

  19. On the Surface • Temperatures at surface mechanical strength of rocks significantly lowered • Over time (~1BY) many topographic features would “disappear” • Muting of many topographic effects • High topography (Ishtar Terra) must be young features • Composition of rocks at surface as measured by Venera landers • Basalts • Different from primordial meteorites • Alkali basalts or granites • Evidence of extensive differentiation, partial melting

  20. On the Surface • Seven Soviet landers successfully reached surface and returned information • Rocks show evidence of geologic processes • Cratering • Volcanism • Layering • Fracturing (tectonics) • Chemical and mechanical weathering • Aeolian transportation • No hydrologic activity • Thin regolith compared to Lunar, Earth or Martian surfaces

  21. Golubkina Crater • Magellan radar image of complex crater • Named after the Russian sculptor Anna Golubkina • 30 km diam. crater characterized by terraced inner walls and a central peak • Typical of large impact craters on the Earth, Moon and Mars • Terraced inner walls – • Take shape late in the formation of an impact crater • Due to the collapse of the initial cavity created by the meteorite impact • The central peak – • Forms due to the rebound of the inner crater floor

  22. Golubkina Crater • This is a computer generated, 3D perspective view of Golubkina crater • Complex crater form w/central peak • Flat-floored crater interior (possible melt) • Vertical exaggeration in this image is about 20 x

  23. Crater Mead • Largest known crater on Venus • Named after Margaret Mead, American anthropologist • Measures 280 km in diam • Classified as a multi-ring crater • Innermost ring is thought to be the rim of the original crater cavity • Irregular, radar-bright crater ejecta crossing the radar-dark floor terrace and adjacent outer radar-bright ring suggests that the terrace floor region is likely down-dropped and tilted outward, forming a concentric ring-fault

  24. Balch Crater • This remarkable half crater is located in the rift between Rhea and Theia Montes in Beta Regio • (Radar illumination is from the left) • ~37 km in diam. • Cut by many fractures or faults since it was formed • Eastern portion was partially destroyed during the formation of a fault-valley • Measures up to 20 km wide • North-south profile through the center of this crater resulted from the down dropping and removal of most of the eastern half of the crater • Rifting shows evidence of vertical movement but no horizontal component indicative of tectonic forces

  25. Wanda CraterAkna Mountains • Mtns. form the western edge of Lakshmi Planum • Wanda Crater, upper right • Diameter of 18 km (11 mi) • Doesn't appear deformed by tectonics but material from the Akna Mountains appears to have collapsed into it • Area of image is about 200 km long x 125 km wide

  26. Alcott Crater • Magellan detected few impact craters in the process of being resurfaced by volcanism • Alcott is the largest of these craters with a diam. of 63 km • The trough-like depression (lower left) is a rille through which lava once flowed • Open lava tube • Remnants of rough radial ejecta is preserved outside the crater's southeast rim • Important to our understanding of resurfacing rates on Venus by volcanism • Note older, rougher terrain in upper right of image

  27. Barton Crater • 54-km diam. crater • Size at which craters on Venus begin to possess peak-rings instead of a single central peak • The floor is flat and radar-dark • Indicates possible infilling by lava flows sometime following the impact • Central peak-ring is discontinuous and appears to have been disrupted or separated during or following the cratering process • Name has been proposed by the Magellan Science Team, after Clara Barton, founder of the U. S. Red Cross; the name is tentative pending approval by the IAU

  28. Carson Crater • Venusian impact craters are frequently surrounded by radar-dark halos • Several of these special craters have halos that are parabolic in shape, and are very long, extending hundreds of kms • The darkness of the emissivity data indicates a smooth surface • Halos may be thick, smooth sediment deposits formed when incoming projectiles crashed into the surface • The black strips represent missing data

  29. Atmospheric Effects on Ejecta Distribution • Large impact crater about 30 km in diam. surrounded by a fresh ejecta blanket • Extreme brightness of the blanket is due to its roughness and its ability to scatter the radar signals that are used to collect these images • Missing section of the ejecta blanket (NW) is due to atmospheric blast that followed the impactor as it crashed through the Venusian atmosphere

  30. Crater Cluster • A small projectile broke up in the atmosphere to form four smaller impactors that struck nearly simultaneously to form this crater cluster • Note overlying ejecta blankets and indistinct, broken, irregular rims

  31. Sapas Mons • Sapas Mons is a large volcano ~400 kms in diameter and 1.5 kms high • The summit consists of two mesas with flat to slightly convex tops and smooth surfaces that appear radar-dark • The sides of the volcano show bright overlapping flows that provide the edifice with a roughly radial outline • Many of the flows appear to be flank eruptions • Radial fractures transect the flows to the east and south • Darker flows in the southeast quadrant are smoother flows

  32. Pyroclastic Cones • The cone volcanoes in this cluster are about 2 kms in diameter, 200m high, with 12° steep slopes overlying a fracture network in Niobe Planitia • Some cones are cut by younger, more widely spaced, north-striking fractures with curvilinear outlines

  33. A) Lakshmi Planum light and dark surfaces equivalent to basalt flow types known as pahoehoe (smooth lavas; somewhat specular surfaces) and aa (chunky lavas, better backscatterers) • B) Series of Lava flows emanate from the Sils Mons volcanic source • C) A long channel filled with volcanic flow material, over which a younger flow has straddled is the Ammavaru flow sequence in the Lada region A C B

  34. Myletta Fluctus Flow • One of the longest flows in SS occurs in Lavinia Planitia • ~1000km long • Must be low silica, low viscosity • Mafic basaltic composition • Infilling of crater between arrows

  35. Anemones • “Anemone" volcano • Petal-like lava flows and radiating radar-bright patterns • Normally occur in association with fissure type eruptions • ~40 by 60 kms in size • Has a dark central edifice with bright central flows • Note elongated summit pits and an arcuate graben along southern summit

  36. Cluster of four overlapping domes Domes average about 25 kms in diameter with maximum heights of 750m Pancakes • Interpreted as viscous or thick eruptions of lava coming from a vent on the relatively level ground allowing the lava to flow in an even lateral pattern

  37. CalderasSacajawea Patera • Elliptical caldera 260 by 175 kms forming depression about 2 kms deep • Enclosed by zone of concentric troughs with radar-bright outlines extending outward from the caldera floor • Floor is covered with smooth mottled plains • A small shield measuring 12 kms in diam is transected by one of these features

  38. Domes • This 17.4 km dome shows collapsed margins and landslide deposits • Landslide deposits show hummocky surfaces that extend up to 10 kms out on the plains • Dome is about 1.86 kms high and has a slope of about 23° • In general, the scale of lava domes and collapse features on Venus is orders of magnitude larger than that on Earth • Mt. Elden is ~2km across &

  39. Mantle melting and convection • Different scales produce different features • Large shield volcanoes = small bodies of magma • Volcanic rises = large-scale mantle upwelling • Coronae = significant melt with smaller or more short-lived upwellings • Larger plumes also yield larger collapse features

  40. Arachnids • As the name suggests, arachnoids are circular to ovoid features with concentric rings and a complex network of fractures extending outward • The arachnoids range in size from approximately 50 kms to 230 kms in diam

  41. Arachnids • Believed to be igneous related • Buoyant plume rises causing crust to stretch and thin • Crust may not be pierced and plume widens, flattens and spreads • As plume cools it sinks causing secondary tensional deformation • Result is uplifted circular mountain ring surrounding central depression

  42. Coronae • Unlike Earth, Venus shows no evidence of plate tectonics • Process that helps release interior heat • One way Venus releases heat is by the formation of a large number of features called coronae • Circular patterns of fractures thought to form when hot material beneath the crust pushes up, warping the surface • Often accompanied by vast lava flows. • Width of image area: 528 km

  43. Fotla Corona • Named after the Celtic fertility goddess • It is located in a vast plain to the south of Aphrodite Terra • Just north (top) of this corona is a flat-topped pancake dome, about 35km in diam • Another pancake dome is located inside the western (left) part of the corona • There is also a smooth, flat region in the center of the corona, probably a relatively young lava flow • Complex fracture patterns like the one in the north-east (top-right) of the image are often observed in association with coronae

  44. Novae • Nova - radial network of grabens • Radiate from central point • Extensional faulting • Upward pressure on crust by ascending magmatic plumes stretches overlying crust causing normal faulting • There have been about 50 novae identified on Venus • This Magellan radar image is from the Themis Regio • 250 km in diameter

  45. Dunes • Pattern of bright and dark ripples in the center of this image is an area where loose material was deposited into dunes • The bright streaks of material curve away from small hills, revealing which way the winds were blowing • Stronger winds caused by meteorite impacts may also help create such features • Width of image area: 172 km

  46. Wind Streaks • Comet-like tail trends NE from a volcanic edifice • Volcano, whose basal diameter is 5 km, is a local topographic high that has slowed down northeast trending winds enough to cause deposition of this material • The streak is 35 km long and 10 km wide • Not dust so why so bright? • Large vs small grain sizes

  47. Fracture Network • Complex network of narrow (<1 km) fractures in the center of the image extends ~50 km • Network exhibits tributary-like branches similar to those observed in river systems on Earth (trellis drainage patterns) • Angular intersections of tributaries suggest tectonic control • Appear to be due to drainage of lava along preexisting fractures and subsequent collapse of the surface

  48. Channels • 200km segment of a sinuous channel on Venus • 2 km wide • Common on plains • In some places appear to have formed by lava • Similar to rivers in some respects, with meanders, cutoff oxbows, and abandoned channel segments • Appear to be older as they are crossed by fractures and wrinkle ridges, and are often buried by other volcanic materials • In addition, they appear to run both upslope and downslope, suggesting that the plains were warped by regional tectonism after channel formation

  49. Weathering on Venus • Type of weathering differs with altitude • Hi alt, lo temp • Sulfur in atmosphere reacts w/mafic lavas to form pyrite (FeS2) • Pyrite is highly reflective at radar wavelengths • May be why highlands and mtn. peaks are bright • Lo alt, hi temp • Magnetite and anhydrite are more stable and less reflective

  50. Summary • Earth and Venus formed at approx. same distance from Sun during SS formation • Should be of similar composition and planetary evolution • Cratering, volcanism and vertical tectonics in common • Bulk density and composition in common • Contrast of two planets • Water • Silicic volcanism • Plate tectonics • Young surface • ~0.5 BY • Few impacts scattered evenly across surface • Resurfacing by volcanic events • Catastrophic vs gradual resurfacing • Lack of water • Outgassed early on • No carbonate rx • Thick, dense atmosphere rids Venus of water to space • No lowering of melting temps in mantle • Lack of large volume of granitic rx • No formation of asthenosphere no plate tectonics • Buoyant crust resists subduction • Up- and downwelling dominate • No magnetic field • Rate of rotation • Possibly still some liquid core material

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