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Lesson 5 Venus Venus from Earth At its brightest, Venus is about 60 times brighter than the brightest stars. Venus is the morning or evening “star” • Venus is never more than 47 degrees from the Sun. Why does Venus look this way? 1. The Earth is casting a shadow on Venus 2. Mercury is casting a shadow on Venus 3. We are seeing the day and night side of Venus 4. There are clouds blocking part of Venus . 25% 1 25% 25% 2 3 25% 4 Venus phases • What is Venus’s phase when it is closest to the Earth? . 1. New Venus 2. Full Venus 3. Half-lit 33% 1 33% 2 33% 3 When Venus is close to the Earth we only see the night side of Venus. When it is on the other side of the Sun we see the full Venus • Galileo was the first to see the phases of Venus, using a small telescope. (1610) • The changing size and phases was proof that Venus didn’t orbit the Earth. Instead, Venus had to orbit the Sun. Venus – Basic Properties Venus – Basic Properties • • • • • • • Diameter is 650 km less than Earth’s Mass is 81.5% of Earth’s Virtually a twin to Earth in size and mass. Venus has no moon Venus atmosphere is 90 times that of Earth Surface temperature is ~ 870o F everywhere. Always under cloud cover • Venus rotates on its axis very slowly (225 Earth Days) and in the opposite direction of that of the other planets. • On Venus the Sun would rise in the west and set in the East. • On Venus, a year is 1.92 Venus days long. So if you were on Venus you would have about 2 days each year. • The slow rotation and small differences in surface temperature around the planet means wind speeds are very slow on Venus. Virtually no wind erosion as on Mars. • We saw on Mars that there has been a great deal of wind erosion. • Venus has virtually one global temperature with only small variations. • Would you expect Venus to also have lots of wind erosion on its surface? . 1. Yes. Venus has a thick atmosphere and is very hot. This should cause enormous 33% 33% winds 2. Yes. Since Venus rotates slowly winds should be able to blow from the poles to the equator 3. No. There are no temperature differences so wind will not develop. 1 2 33% 3 • Venus rotates on its axis very slowly and in the opposite direction of that of the other planets. • On Venus the Sun would rise in the west and set in the East. • On Venus, a year is 1.92 Venus days long. So if you were on Venus you would have about 2 days each year. • The slow rotation and small differences in surface temperature around the planet means wind speeds are very slow on Venus. Virtually no wind erosion as on Mars. Venus from outer space • Venus is always shrouded in thick clouds. The atmosphere is almost completely carbon dioxide (CO2). • The cloud decks seen from space are composed mostly of sulfur dioxide (SO2). • There is virtually no water in the atmosphere of Venus. Topographical Map Red highest elevation, blue lowest Earth topographical map Earth Active Volcanoes Venus volcanoes Is there plate tectonics occurring on Venus? Is there plate tectonics occurring on Venus? 1. Yes 2. No 50% 1 50% 2 What type of volcanoes do you expect? What type of volcanoes are on Venus? 1. Strato-volcanoes 2. Shield volcanoes 3. A mixture of the two. 33% 1 33% 2 33% 3 Venus volcanoes Maat Mons Gula Mons All Venus volcanoes are shield. • Large shield volcanoes • Pancake Domes (smaller, sometimes form along fissures) • Corona (uplifts in crust causing tectonic features) • Arachnoids (spider-like volcanoes that have sunk back into the surface) Large shield volcano Lava Flow and channels Mylitta Fluctus Lava Flow and channels Atla Regio about 1000 km long Helen Planitia Long lava flow channels (~1200 km long) which show signs of being covered by later lava flow. Pancake volcanoes forming in a line along fissure Flat top, pancake domes suggest that the lava was of higher viscosity • If pancake domes form along crustal fissures, why might they have higher viscosity? . 50% that 1. There must be a subduction zone mixes crustal material into the mantle magma. 2. Mantle magma emerging up through the fissure probably melts the crust which makes the magma of higher viscosity 1 50% 2 Corona features Caused by hot mantle material uplifting and sinking over and over again. Arachnid volcanoes are probably volcanic domes which sunk back down when magma retreated About 1000 impact craters on Venus Impact craters • On Venus there are no impact craters smaller than 3 km. Most are around 10 km or bigger. • Why do you think this is? . 1. All the smaller craters are destroyed by geologic activity33% 2. Smaller meteors can’t make it through the thick Venus atmosphere 3. Venus only gets hit by big objects. 1 33% 2 33% 3 Distribution of Impact craters Impact craters • On Venus there are no impact craters smaller than 3 km. Most are around 10 km or bigger. This is due to the protection of the extremely thick atmosphere. • The impact craters are randomly distributed across the surface of Venus. • Density is about 1.9 craters/million km2. This is the same everywhere on the surface. • What does this suggest? . 1. The surface of Venus is the 33% same age globally. 2. Younger regions on the surface have been hit more frequently in the recent past. 3. Venus is similar to the highlands of the Moon 1 33% 2 33% 3 Lunar Site Fra Mauro Cayley Apollo 11 Apollo 15 Apollo 12 Copernicus crater rim Crater Density Age (10km/1 million km2) 550 (billions of years) 3.94 430 120 97 3.77 3.55 3.40 70 20 3.28 0.90 Impact craters • On Venus there are no impact craters smaller than 3 km. Most are around 10 km or bigger. This is due to the protection of the extremely thick atmosphere. • The impact craters are randomly distributed across the surface of Venus. • Density is about 1.9 craters/million km2 • Lunar density for a 0.9 billion years old surface is 20 craters/million km2 Piecing the evidence together. • Few impact craters that are randomly distributed. • No plate tectonics. • Volcanoes are randomly distributed across the surface. • What does this suggest about the surface of Venus? . 1. There is a combination of very old surfaces and very young surfaces on 33% 33% Venus 2. Craters near volcanoes are destroyed while other places retain their ancient craters 3. Venus must have eruptions on a global scale that resurfaces the entire planet. 1 2 33% 3 Piecing the evidence together. • Few impact craters that are randomly distributed. (Means the global surface of Venus is about the same age). • No plate tectonics. (Means pressure release has to come in the form of magma plumes) • Volcanoes are randomly distributed across the surface. (Means that eruptions are not just in local regions like on Mars) Geology on Venus • Venus appears to resurface nearly the entire planet at the “same” time, about 200 – 600 million years ago. (Possibly over a 100 million year period) • Since there is no plate tectonics, pressure and temperature builds inside of Venus and is finally released globally, resurfacing the entire planet. • Activity then slows until pressure rebuilds. • This is likely a cyclic process.