april 11, 2006astronomy 20101 chapter 9 earth-like planets: venus and mars venus and mars resemble...
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![Page 1: April 11, 2006Astronomy 20101 Chapter 9 Earth-Like Planets: Venus and Mars Venus and Mars resemble Earth more than any other planets. Is it possible that](https://reader036.vdocument.in/reader036/viewer/2022062714/56649d565503460f94a34839/html5/thumbnails/1.jpg)
April 11, 2006 Astronomy 2010 1
Chapter 9Earth-Like Planets: Venus and Mars
• Venus and Mars resemble Earth more than any other planets.
• Is it possible that life exists or did exist on either?
• One day, will we be able to establish a human presence on Venus or Mars?
• Can studying these planets give us clues to Earth’s origins or future.
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April 11, 2006 Astronomy 2010 2
9.1.1 Appearance of Venus• Venus gets closer to Earth than any other planet.
• It appears as a bright object near the Sun after sunset or before sunrise.
• Venus goes through phases, like the Moon.
• Venus is shrouded in thick clouds making it impossible to view the surface from Earth.
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April 11, 2006 Astronomy 2010 3
9.1.1 Appearance of Mars• About every 24 months the Earth and Mars are at their closest.
• Mars is reddish due to iron oxides (rust) in the soil.
• Around 1900, Percival Lowell thought he saw canals on Mars!
• Mars has polar ice caps, thin clouds, and dust storms.
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April 11, 2006 Astronomy 2010 4
9.1.2 Rotation of the Planets• The rotation of Mars has been measured
by observing features on the planet over a very long time, about 200 years.
• Mars’ sidereal rotation period is 24 h 37m 23s, about 40min longer than Earth’s.
• The rotation of Venus is measured using radar, but unlike Mercury, the radar is used to observe surface features and watch them rotate.
• Venus’ sidereal rotation period is 243 days!
• Venus rotates backwards (retrograde)!!
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April 11, 2006 Astronomy 2010 5
Properties of Earth, Venus, and Mars
Earth Venus Mars
Semi major axis (AU) 1.00 0.72 1.52
Period (Earth years) 1.00 0.61 1.88
Mass (Earth = 1) 1.00 0.82 0.11
Diameter (Earth = 1) 1.00 0.95 0.53
Density (g/cm3) 5.5 5.3 3.9
Surface Gravity (Earth = 1)
1.00 0.91 0.38
Escape velocity (km/s) 11.2 10.4 5.0
Rotation period 23.9 hours
243 days 24.6 hours
Surface Area (Earth = 1) 1.00 0.90 0.28
Atmospheric Pressure (bar)
1.00 90 0.007
• Compare some properties of these planets.
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April 11, 2006 Astronomy 2010 6
9.1.3 Basic PropertiesVenusVenus
• Very similar to Earth• High geological activity
• Thick atmosphere of CO2
• Surface temperature of 730K (over 850 F).
• Atmospheric pressure of 90 bar, equivalent to 1km under the ocean.
MarsMars• Smaller than Earth• Thin atmosphere• Significant past geological activity
• Probably had a thick atmosphere and liquid water in the past.
• Could have supported life.
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April 11, 2006 Astronomy 2010 7
9.2 The Geology of Venus• Being of similar size and
composition to Earth, we might expect Venus to have similar geology.
• More spacecraft have visited Venus than any other planet.– 1962 U.S. Mariner 2 flyby– 1970 Soviet Venera 7 lands on Venus
and sends back pictures for 23 minutes (heat).
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April 11, 2006 Astronomy 2010 8
More Missions to Venus– 1970s Venera craft measure soil and atmosphere.
– 1970s U.S. Pioneer Venus -- radar map.
– 1980s Venera 15 and 16 radar orbiters.
– 1991-3 Magellan radar maps with 100m resolution.
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Globe of Venus constructedfrom Magellan radar maps.
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April 11, 2006 Astronomy 2010 9
Venus Express: Orbiting Venus
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April 11, 2006 Astronomy 2010 10
Venus Express• Built by the European Space Agency (ESA)
• Launched on a Russian Soyuz rocket in November 2005.
• Arrived at Venus April 11, 2006.
• Will study Venus for 2 to 5 years, especially to understand the greenhouse effect.
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April 11, 2006 Astronomy 2010 11
Radar Maps of Venus
N
S
1
2
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April 11, 2006 Astronomy 2010 12
9.2.3 Venus: Craters and Surface Age
• Count craters to estimate surface age.
• Largest crater called Meade, 275km in diameter.
• Thick atmosphere stops only small projectiles.
• Almost no craters smaller than 10km in diameter.
• Count larger craters and estimate surface age at 500 million years.
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April 11, 2006 Astronomy 2010 13
9.2.4 Volcanoes on Venus• Significant
volcanism.• Largest volcano,
Sif Mons, is wider but shorter than Mauna Kea.
• Some volcanoes produce “pancake domes”.
• Many volcanoes don’t make it to the surface, but push up the crust in bulges called coronae.
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April 11, 2006 Astronomy 2010 14
9.3 The Massive Atmosphere of Venus
• Atmosphere is 96% CO2, 3.5% nitrogen and trace amounts of H2O, H2SO4.
• The CO2 traps heat on the planet via the greenhouse effect.
• Runaway greenhouse effect.
• The surface temperature is more than 700 Kelvin (850F).
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April 11, 2006 Astronomy 2010 15
The Birth of Venus
• Backward rotation could mean that Venus suffered a giant impact early in its history.
• The runaway greenhouse effect explains why Venus has such a massive atmosphere and high surface temperatures.
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April 11, 2006 Astronomy 2010 16
9.4 The Geology of Mars• Humans could survive on Mars, making it more interesting.
• Spacecraft have visited and landed on Mars. – 1965: Mariner 4 fly by
– 1971: Mariner 9 orbited
– 1976: Vikings 1 and 2 landed
– 20 years pass with 2 failed missions to Mars.
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April 11, 2006 Astronomy 2010 17
9.4.1 Spacecraft Exploration of Mars
– 1997: Pathfinder lands on Mars and Global Surveyor orbits.
– Several more failed space missions.
– 2004: 4 spacecraft to Mars, 2 U.S., 1 ESA, 1 Japan. (Japanese craft failed to orbit, ESA rover, Beagle, didn’t function).
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April 11, 2006 Astronomy 2010 18
9.4.2 Global Properties of Mars• Mars is half
Earth’s diameter.• Small metal core.• No magnetic field.
• We have good maps of Mars showing:– Olympus Mons: highest peak in the solar system.
– Vallis Marineris: largest canyon in the solar system.
– Old highlands and younger lowlands.
Olympus Mons
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April 11, 2006 Astronomy 2010 19
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April 11, 2006 Astronomy 2010 20
9.4.3 Volcanoes on Mars• The lowland plains seem to be formed 3 to 4 billion years ago– Lava flows
• Largest volcanoes on the Tharsis bulge.
• 3 shown at right• Olympus Mons is largest, larger than Mauna Loa in Hawaii
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April 11, 2006 Astronomy 2010 21
9.4.4 Martian Cracks and Canyons• Valles Marineris
is the largest canyon in the solar system.
• Formed by cracking in the Tharsis bulge
• L.A. to N.Y.• Landslides in valley are evidence of erosion (water?).
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April 11, 2006 Astronomy 2010 22
9.5 Martian Polar Caps and Climate
• Thin atmosphere, like Earth’s 30km up.
• Mostly CO2.• Clouds of dust, H2O, and CO2.
• Seasonal ice caps of CO2 (dry ice).
• Permanent polar caps (south at left) have H2O.
• Ice in the soil (permafrost).
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April 11, 2006 Astronomy 2010 23
9.5.4 Climate Change on Mars
• Mars suffers from the runaway refrigerator effect.– Mars might have had a much thicker atmosphere and milder climate in the past.
– Mars has smaller surface gravity than Venus or Earth.
– Atmospheric gases can escape into space, cooling off the planet (evaporative cooling).
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April 11, 2006 Astronomy 2010 24
9.5.5 Life on Mars
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April 11, 2006 Astronomy 2010 25
Search for Life on Mars• Life as we know it needs water.• If Mars had water in the past, life could have developed.
• We’ve tried looking for signs of life in a variety of ways, so far with negative results.
• It could be that UV light has sterilized the surface -- could microbes be underground?
• Some scientists claim that a meteorite from Mars shows signs of microbial life. (next)
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April 11, 2006 Astronomy 2010 26
Martian Meteorite
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April 11, 2006 Astronomy 2010 27
Discussion Question• This is to review some of the material just presented.
• First answer the following question:– Venus, Earth, and Mars have mountains. What are two factors that may explain why Mars has the largest mountain, though it is the smallest of the three planets.
• Second pass your answer to another person for discussion and grading. Please sign your name at the bottom of the answer you are grading.