GEOL3045: Planetary Geology Lysa Chizmadia Venus From Mariner to Venera to Venus Express Lysa Chizmadia Venus From Mariner to Venera to Venus Express

Introduction  Second planet from the Sun  Distance = 1.1 x 10 8 km  0.72 AU  Diameter = 1.2 x 10 4 km  Mass = 4.9 x kg  Very circular orbit  Eccentricity < 1%  Aphelion: 1.09 x 10 8 km  Perihelion: 1.07 x 10 8 km  Retrograde rotation  From east to west  Venusian day = 243 days  Venusian year = 225 days  Second planet from the Sun  Distance = 1.1 x 10 8 km  0.72 AU  Diameter = 1.2 x 10 4 km  Mass = 4.9 x kg  Very circular orbit  Eccentricity < 1%  Aphelion: 1.09 x 10 8 km  Perihelion: 1.07 x 10 8 km  Retrograde rotation  From east to west  Venusian day = 243 days  Venusian year = 225 days Image from:  Shows phases  Supported Copernicus’ heliocentric theory  Mean surfaces temperature = 462  C  ~isothermal  Hotter than Mercury

Earth’s Twin Planet  Similar sizes:  1.2 x 10 4 km (95% of  )   = 1.3 x 10 4 km  Similar masses:  4.9 x kg (80% of  )   = 6.0 X kg  Similar densities  5.25 g/cm 3 vs g/cm 3 vs.  Similar bulk compositions  Young surfaces  Recent geologic activity  Including volcanism & weathering  Similar sizes:  1.2 x 10 4 km (95% of  )   = 1.3 x 10 4 km  Similar masses:  4.9 x kg (80% of  )   = 6.0 X kg  Similar densities  5.25 g/cm 3 vs g/cm 3 vs.  Similar bulk compositions  Young surfaces  Recent geologic activity  Including volcanism & weathering Rare impact crater on Venus Images from: Relative sizes of the terrestrial planets

Venusian Geography  Highlands (~ continents)  Ishtar Terra ~ size of Australia  Northern hemisphere  Interior high plateau: Lakshmi Planum  Surrounding by highest mountains  Maxwell Montes  Highest mts have high albedo substance  Speculation: Te & PbS  Aphrodite Terra ~ size of S. America  Equator  Broad depressions (~ ocean basins)  Atalanta Planitia  Guinevere Planitia  Lavinia Planitia  Highlands (~ continents)  Ishtar Terra ~ size of Australia  Northern hemisphere  Interior high plateau: Lakshmi Planum  Surrounding by highest mountains  Maxwell Montes  Highest mts have high albedo substance  Speculation: Te & PbS  Aphrodite Terra ~ size of S. America  Equator  Broad depressions (~ ocean basins)  Atalanta Planitia  Guinevere Planitia  Lavinia Planitia Image from: Magellan radar map (false color) Image from: Map of Venus, higher elevations in reds & yellows

Venusian Atmosphere  Densest of all terrestrial planets  96.5% CO 2 & 3.4% N 2  times thicker than   Greenhouse effect  Responsible for high Ts  Receives 25% of sunlight as Mercury  Clouds of CO 2 & H 2 SO 4  Atm contains 0.015% SO 2  Has intermittent lightning  Indicates weathering  Venus Express  Studying atmosphere  Densest of all terrestrial planets  96.5% CO 2 & 3.4% N 2  times thicker than   Greenhouse effect  Responsible for high Ts  Receives 25% of sunlight as Mercury  Clouds of CO 2 & H 2 SO 4  Atm contains 0.015% SO 2  Has intermittent lightning  Indicates weathering  Venus Express  Studying atmosphere Images from: Venus in visible light Venus in UV light

Venusian Volcanism  Magellan’s radar showed much of Venus is covered in lava flows  Several shield volcanoes  E.g. Sif Mons & Sapas Mons  >152 volcanic domes  Flat-top domes called pancake domes  Consistent w/ viscous lavas  High silica lavas?  Magellan’s radar showed much of Venus is covered in lava flows  Several shield volcanoes  E.g. Sif Mons & Sapas Mons  >152 volcanic domes  Flat-top domes called pancake domes  Consistent w/ viscous lavas  High silica lavas? Sif Mons Pancake volcanoes in Alpha Regio region Images from: Radial lava flows Sapas Mons

Coronae & Arachnoids  Coronae  Circular raised structures surrounded by ridges & grooves & radial lines  Seem to be collapsed domes over large magma chambers  E.g. Crater Lake  Arachnoids  Ovoid features w/ concentric rings & complex fracture networks  Similar but smaller than coronae  Possibly precursor to coronae  Coronae  Circular raised structures surrounded by ridges & grooves & radial lines  Seem to be collapsed domes over large magma chambers  E.g. Crater Lake  Arachnoids  Ovoid features w/ concentric rings & complex fracture networks  Similar but smaller than coronae  Possibly precursor to coronae Image from: Pandora Coronae Images from: Ba’het CoronaeArachnoids

Prominent U.S. Satellites  Mariner 2:  First satellite to visit Venus  Flyby in December 1962  Discovered Venus is very hot (~800  C) w/ dense CO 2 -rich atmosphere  Pioneer Venus in 1978  Orbiter & 4 atmospheric probes  Made 1st high quality map of Venus  Magellan in 1989  Mapped 98% of surface  Gravity field map for 95% of surface  Mariner 2:  First satellite to visit Venus  Flyby in December 1962  Discovered Venus is very hot (~800  C) w/ dense CO 2 -rich atmosphere  Pioneer Venus in 1978  Orbiter & 4 atmospheric probes  Made 1st high quality map of Venus  Magellan in 1989  Mapped 98% of surface  Gravity field map for 95% of surface

Venera 7, 9 & 10  Venera 7 in 1970  1st probe to return surface data from another planet  Venera 9 & 10 in 1975  1st spaceship to land on another planet  Clouds km thick  Pressure 90 atm  Temperature 485  C  Windspeed 3.5 m/s  Also Venera  Detected possible seismic activity  Observed strong lightning  Discovered pancake volcanoes, coronae & arachnoids  Venera 7 in 1970  1st probe to return surface data from another planet  Venera 9 & 10 in 1975  1st spaceship to land on another planet  Clouds km thick  Pressure 90 atm  Temperature 485  C  Windspeed 3.5 m/s  Also Venera  Detected possible seismic activity  Observed strong lightning  Discovered pancake volcanoes, coronae & arachnoids Image from: Venusian surface from Venera 9 Image from: Venusian surface from Venera 9 & 10 Image from: Venusian surface from Venera 13

Summary  Earth’s twin in size & bulk composition  Also, young surfaces  Geologic activity & weathering  Densest atmosphere for terrestrial planets  ~90 times higher than Earth  Greenhouse effect keeps T high & constant  Lightning & “snow” indicate weather  Prominent features include  Volcanoes (shield & pancake)  Coronae (magma rising)  Arachnoids (collapsed volcanoes)  Earth’s twin in size & bulk composition  Also, young surfaces  Geologic activity & weathering  Densest atmosphere for terrestrial planets  ~90 times higher than Earth  Greenhouse effect keeps T high & constant  Lightning & “snow” indicate weather  Prominent features include  Volcanoes (shield & pancake)  Coronae (magma rising)  Arachnoids (collapsed volcanoes)