Venus The Rotation of Venus Almost all planets rotate counterclockwise, i.e. in the same sense as orbital motion. Exceptions: Venus, Uranus and Pluto Venus rotates clockwise, with period slightly longer than orbital period. Possible reason:
Off-center collision with massive protoplanet
The Atmosphere of Venus UV image Extremely inhospitable: 96 % carbon dioxide (CO 2 ) 3.5 % nitrogen (N 2 ) Rest: water (H 2 O), hydrochloric acid (HCl), hydrofluoric acid (HF) 4 thick cloud layers ( -> surface invisible to us from Earth). Very stable circulation patterns with high-speed winds (up to 240 km/h) Extremely high surface temperature up to 745 K (= 880 o F) Very efficient “greenhouse”! 0
Venus has a runaway greenhouse effect
because its atmosphere is rich in CO 2
The Surface of Venus
Early radar images from Earth and satellites revealed mountains, plains, craters. However the surface is DOMINATED BY VOLOCANISM
Venera 13 photograph of surface of Venus : Colors modified by clouds in Venus’ atmosphere
More details was obtained from orbiting and landing spacecraft:
After correction for atmospheric color effect: 0
Radar Map of Venus’ Surface Surface features shown in artificial colors.
Scattered impact craters
Smooth lava flows
“ Blob” or Hot-Spot Tectonics
Rather than plate tectonics, Venus appears to have many mantle hot spots (upwelling mantle currents or plumes).
What might this mean about the crust of Venus?
On earth, mantle plumes couple with plate movements to make island chains. What would be formed without the plate movement?
Venus is dominated by…volcanos Maat Mons
Coronae or Arachnoids
Enormous circular structures with raised rims and lowered floors.
resemble volcanic calderas.
have a sunken “moat” just inside the rim
Shield Volcanoes Found above hot spots: Fluid magma chamber , from which lava erupts repeatedly through surface layers above. All volcanoes on Venus and Mars are shield volcanoes 0
Volcanic Features on Venus Baltis Vallis: 6800 km long lava flow channel (longest in the solar system!) Coronae: Circular bulges formed by volcanic activity Aine Corona Lava flows Pancake Domes: Associated with volcanic activity forming coronae Some lava flows collapsed after molten lava drained away 0
What’s Missing? Craters
Venus has few craters. Craters tend to be larger than 5 km in diameter. Why?
Venus has few craters for 2 reasons:
lava flows have covered many
small meteors have difficulty making it to the surface.
Craters on Venus Nearly 1000 impact craters on Venus’ surface: -> Surface not very old. No water on the surface; thick, dense atmosphere -> No erosion -> Craters appear sharp and fresh 0
Venus Magnetic Field
Complicated history; still poorly understood.
Very similar to Earth in mass, size, composition, density, but no magnetic field -> Core solid?
Solar wind interacts directly with the atmosphere, forming a bow shock and a long ion tail.
CO 2 produced during outgassing remained in atmosphere (on Earth: dissolved in water).
Any water present on the surface rapidly evaporated -> feedback through enhancement of greenhouse effect
The Little Desert Planet 1
Diameter ≈ ½ Earth’s diameter
Very thin atmosphere, mostly CO 2
Rotation period = 24 h, 40 min.
Axis tilted against orbital plane by 25 o , similar to Earth’s inclination (23.5 o )
Seasons similar to Earth -> Growth and shrinking of polar ice cap
Crust not broken into tectonic plates
Volcanic activity (including highest volcano in the solar system)
around the sun = 687 days
The Atmosphere of Mars Very thin: Only 1 % of pressure on Earth’s surface 95 % CO 2 Even thin Marsian atmosphere evident through haze and clouds covering the planet Occasionally: Strong dust storms that can enshroud the entire planet. 0
The Atmosphere of Mars (II) Most of the Oxygen bound in oxides in rocks -> Reddish color of the surface 0
History of Mars’ Atmosphere
Initial atmosphere from outgassing.
Small mass of Mars; moderate temperatures
Molecule velocity greater than escape velocity: -> gasses escape into space .
Mars has lost all lighter gasses; retained only heavier gasses (CO 2 ).
The Atmospheric Temperature Structures of the Terrestrial Planets 0
Geology of Mars Northern Lowlands: Free of craters; probably re-surfaced a few billion years ago. Southern Highlands: Heavily cratered; probably 2 – 3 billion years old. Possibly once filled with water. 0
Surface Features Overview
N vs. S differences
Polar Ice Caps
Evidence of Past Water
North vs. South
Typical N. hemisphere region
Typical S. hemisphere region
Olympus Mons Alba Patera (Volcanoes) Aligned Shield Volcanoes Valles Marineris
Volcanoes on Mars
2 types of volcanoes: shields and pateras.
Shield volcanoes are wide and low. Because of the low viscosity of lava on Mars.
The main shield volcanoes on Mars are Olympus Mons, and the aligned shield volcanoes: Ascraeus Mons Parvonis Mons Arsia Mons 41
If one edge were in Lancaster, the opposite edge would be in Chicago!
At 15 miles or 80,000 feet, the crater is above Mars’ thin atmosphere.
You could stand on Mars’ surface and be in space at the same time!
27 kilometers above mean datum.
3x higher than Mt. Everest
2.6x taller than Mauna Kea (from sea floor base to caldera)
Slope is only 2.5 o .
Surrounded by an escarpment up to 6 km high.
Caldera is 85 km x 60 km.
Olympus Mons 46
The other type of volcano is a patera – a huge crater with almost no slope around it. Larger, but lower, than shield volcanos. Apollinaris patera http://www.the-planet-mars.com/pictures/Apollinaris-Patera-volcano.jpg 49
Alba Patera – almost no slope, huge caldera 50
From high to low – the Planitia
9 km deep
2100 km across
rim is 1.25 km high
impact debris thrown out to a distance of 4000 km
5 km deep
several deep channels flow into it from surrounding terrain
up to 10 km deep (6-7 times deeper than our Grand Canyon)
NOT formed by flowing water! (but possibly modified by water)
How was it formed?
Near the eastern end of the Valles Marineris are huge canyons called “outflow channels”.
Hidden Water on Mars No liquid water on the surface: Would evaporate due to low pressure. But evidence for liquid water in the past: Outflow channels from sudden, massive floods Collapsed structures after withdrawal of sub-surface water Valleys resembling meandering river beds Gullies, possibly from debris flows Central channel in a valley suggests long-term flowing water 0
Hidden Water on Mars (II) Gusev Crater and Ma’adim Vallis: Giant lakes might have drained repeatedly through the Ma’adim Vallis into the crater. 0
Evidence for Water on Mars Large impacts may have ejected rocks into space. Galle, the “happy face crater” Meteorite ALH84001: Identified as ancient rock from Mars. Some minerals in this meteorite were deposited in water -> Martian crust must have been richer in water than it is today. 0
Ice in the Polar Cap Polar cap contains mostly CO 2 ice, but also water. Multiple ice regions separated by valleys free of ice. Boundaries of polar caps reveal multiple layers of dust, left behind by repeated growth and melting of polar-cap regions. 0
The Moons of Mars Phobos (Fear) Deimos (Demons) Two small moons: Phobos (diameter ~ 25 km) and Deimos (diameter = 12 km). Too small to pull themselves into spherical shape. Very close to Mars; orbits around Mars faster than Mars’ rotation. Typical of small, rocky bodies: Dark grey, low density. Probably captured from outer asteroid belt. 0
Terrestrial Planets Mercury Venus Earth Mars
Natural Climate Change When Good Planets go Bad What happened to them?
The Terrestrial Planets H2O and CO2 clouds, dust Winds, dust storm -81F 0.007bar 95% CO 2 2.7% N 2 Mars none none Day:260F Night: 280F 10 -14 bar He, Na, Ar Moon H2O clouds, pollution Winds, hurricanes, rain, snow 60F 1 bar 77% N 2 21% O 2 H 2 O Earth Sulfuric acid clouds Slow winds, acid rain 880F 90 bars 96% CO 2 3.5% N2 Venus none none Day: 800F Night: -280F 10 -14 bar He, Na, O Mercury Clouds, Hazes Winds, Weather Ave Surface Temp. Surface Pressure Atmos. Compsn. World
CO 2 and H 2 O main gases.
Mt. St. Helens
Thermal escape “boiling away” by temperature.
“ Knocking away” by solar wind particles.
UV-rays break molecules into smaller atoms.
Lighter atoms boil away.
Absorbed by surface
“ Blasted away” by impacts
Atoms have mass.
Attracted to planet by gravity.
Temperature is measure of atoms motion.
High temperature = high velocity: escape velocity if too light.
Sun blows off solar wind:
Billiards with atmosphere (if no magnetosphere).
Atoms held together in molecules by electromagnetic forces.
UV-rays source of energy.
Break molecular bonds.
Light elements (H) can boil away.
Importance of protective ozone layer.
Rust for O 2 .
Carbonate rocks for CO 2 (when H 2 0 is present)
Pressure = 90 bars.
Temperature = 880 F.
No pole/equator temperature difference.
No day/night temperature difference.
No seasonal temperature difference.
No rain hits surface.
Venera 13 and 14 color images from red, green and blue filters.
Copyright: Don P. Mitchell – Mentallandscape.com
What went wrong on Venus?
Same size as Earth.
Same outgassing as Earth.
Same CO 2 content.
What happened to atmospheric H 2 O?
Higher initial temperature.
What went wrong on Venus?
Higher initial temperature.
More water evaporates.
Atmosphere can hold more H 2 O before rains.
H 2 O is greenhouse gas – increases temp.
More water evaporates.
All H 2 O evaporates.
No oceans, seas or lakes.
… it gets worse on Venus.
No water for CO 2 to react.
Increases greenhouse effect further.
UV-rays dissociate H 2 O.
H lost to space.
Result, 100% of CO 2 in atmosphere.
Runaway greenhouse effect.
Hot, dry, Venus today.
Good scientific theory?
Venus once like Earth?
Pressure just below triple point of water:
Temperature below freezing:
No rain, some clouds, dust, ice caps.
The War of the Worlds www.cloudster.com/Sets&Vehicles/WarOfTheWorlds drzeus.best.vwh.net / wotw/illus/interior.html 27
www.retrocrush.com / 100monsters/70.html 28
“ This is Glub, sitting in for Tom Dunn on the ‘ Eleven O’Clock News,’ and I wish to announce that there has been a rather sudden and sweeping change in your government. 29
What went wrong on Mars?
Too small – core cools
Core cools – magnetic field stops (not magnetosphere).