GEOL3045: Planetary Geology
Lysa Chizmadia
Venus
From Mariner to Venera to Venus
Express
Introduction
 Second planet from the
Sun
 Distance = 1.1 x 108 km
 0.72 AU
 Diameter = 1.2 x 104 km
 Mass = 4.9 x 1023 kg
 Very circular orbit
 Eccentricity < 1%
 Aphelion: 1.09 x 108 km
 Perihelion: 1.07 x 108 km
 Retrograde rotation
 From east to west
 Venusian day = 243 days
 Venusian year = 225 days
Image from:
http://www.nineplanets.org/venus.html
 Shows phases
 Supported Copernicus’
heliocentric theory
 Mean surfaces
temperature = 462C
 ~isothermal
 Hotter than Mercury
Earth’s Twin Planet
 Similar sizes:
 1.2 x 104 km (95% of )
  = 1.3 x 104 km
 Similar masses:
Relative sizes of the terrestrial planets
 4.9 x 1023 kg (80% of )
  = 6.0 X 1024 kg
 Similar densities
 5.25 g/cm3 vs. 5.52 g/cm3 vs.
 Similar bulk compositions
 Young surfaces
 Recent geologic activity
 Including volcanism & weathering
Rare impact crater on Venus
Images from: http://en.wikipedia.org/wiki/Venus
Venusian Geography
 Highlands (~ continents)
 Ishtar Terra ~ size of Australia
 Northern hemisphere
 Interior high plateau: Lakshmi Planum
 Surrounding by highest mountains
 Maxwell Montes
Map of Venus, higher elevations in reds & yellows
Image from: http://en.wikipedia.org/wiki/Venus
 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
Magellan radar map (false color)
Image from: http://www.nineplanets.org/venus.html
Venusian Atmosphere
 Densest of all terrestrial planets
 96.5% CO2 & 3.4% N2
 90-92 times thicker than 
 Greenhouse effect
 Responsible for high Ts
 Receives 25% of sunlight as Mercury
Venus in visible light
 Clouds of CO2 & H2SO4
 Atm contains 0.015% SO2
 Has intermittent lightning
 Indicates weathering
 Venus Express 2005-2009
 Studying atmosphere
Venus in UV light
Images from: http://en.wikipedia.org/wiki/Venus
Venusian Volcanism
 Magellan’s radar showed
much of Venus is covered
in lava flows
 Several shield volcanoes
Sif Mons
 E.g. Sif Mons & Sapas Mons
 >152 volcanic domes
 Flat-top domes called
pancake domes
 Consistent w/ viscous lavas
Radial lava flows Sapas Mons
 High silica lavas?
Pancake volcanoes in Alpha Regio region
Images from: http://www.geology.sdsu.edu/how_volcanoes_work/venus.html
Coronae & Arachnoids
 Coronae
 Circular raised structures
surrounded by ridges & grooves
& radial lines
 Seem to be collapsed domes
over large magma chambers
Pandora Coronae
Image from:
http://www.nineplanets.org/venus.html
 E.g. Crater Lake
 Arachnoids
 Ovoid features w/ concentric
rings & complex fracture
networks
 Similar but smaller than
coronae
 Possibly precursor to coronae
Ba’het Coronae
Arachnoids
Images from:
http://www.geology.sdsu.edu/how_volcanoes_work/venus.html
Prominent U.S. Satellites
 Mariner 2:
 First satellite to visit Venus
 Flyby in December 1962
 Discovered Venus is very hot (~800C) w/
dense CO2-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 30-40 km thick
 Pressure 90 atm
 Temperature 485C
 Windspeed 3.5 m/s
Venusian surface from Venera 9
Image from:
http://www.nineplanets.org/venus.html
Venusian surface from Venera 9 & 10
Image from:
http://en.wikipedia.org/wiki/Venera_10
 Also Venera 11-16
 Detected possible seismic activity
 Observed strong lightning
 Discovered pancake volcanoes,
coronae & arachnoids
Venusian surface from Venera 13
Image from: http://www.solarviews.com/eng/venus.htm
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)