15 February 2005AST 2010: Chapter 9 1 Venus & Mars

15 February 2005AST 2010: Chapter 92 Nearest Planets Venus and Mars resemble Earth more than any other planets But the three are very different from each other Venus and Mars are among the brightest objects in the night sky Intriguing questions: Will we someday be able to visit Venus or Mars? Does alien life exists on either? Can studying these planets give us clues to Earth’s origin, or future? Venus Mars

15 February 2005AST 2010: Chapter 93 Appearance of Venus Venus gets closer to Earth (about 40 million km) than does any other planet Venus sometimes appears as a bright object near the Sun after sunset (an “evening star”) or before sunrise (a “morning star”) Galileo discovered that Venus goes through phases, like the Moon Venus is shrouded by thick clouds, making it impossible to view its surface, even with cameras in orbit around the planet

15 February 2005AST 2010: Chapter 94 Appearance of Mars About every 24 months the Earth and Mars are at their closest (~56 million km apart) Mars is reddish due to the presence of iron oxides (rust) in its soil Around 1900, Percival Lowell thought he saw canals on Mars! It is now generally accepted that what he saw was an optical illusion Mars has polar ice caps, thin clouds, and dust storms Two faces of Mars

15 February 2005AST 2010: Chapter 95 Rotation of Venus and Mars The rotation (spinning) 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 40 minutes longer than Earth’s The rotation (spinning) of Venus is measured using radar, but (unlike Mercury) the radar is used to observe the motion of Venus’ surface features Venus’ sidereal rotation period is 243 days! Surprise: Venus spins in a backward or retrograde direction!!

15 February 2005AST 2010: Chapter 96 Properties of Earth, Venus, and Mars

15 February 2005AST 2010: Chapter 97 Basic Properties Venus Similar to Earth in size, mass, and high geological activity Has thick atmosphere consisting mostly of carbon dioxide (CO 2 ) Atmospheric pressure almost 100 times greater than Earth’s Surface very hot, with temperature of 730K (over 850° F) Mars Rather small in mass and size compared to Earth May have had significant geological activity in the past Has thin atmosphere Probably had thick atmosphere and liquid water in the past Which could have supported life

15 February 2005AST 2010: Chapter 98 The Geology of Venus Venus being similar size and composition to the Earth, we might expect the two planets to have similar geology This is partly true, but Venus does not exhibit the same kind of plate tectonics as the Earth Early missions to Venus: 1962: U.S. Mariner 2 did a flyby 1970: Soviet Venera 7 became the first craft to land on Venus and broadcast back pictures for 23 minutes (before succumbing to heat)

15 February 2005AST 2010: Chapter 99 Missions to Venus More spacecraft have visited Venus than any other planet Additional missions to Venus 1970: more Venera probes made photographs as well as analyzed the soil and atmosphere 1970s: U.S. Pioneer Venus orbiter made the first crude global radar map 1980s: Soviet Venera 15 and 16 radar orbiters made better radar maps : U.S. Magellan spacecraft made radar maps with 100-m resolution Images taken by Venera 13

15 February 2005AST 2010: Chapter 910 Radar Maps of Venus N S 1 2

15 February 2005AST 2010: Chapter 911 Craters and Surface Age of Venus Crater counting used to estimate surface age Largest crater, called Meade, 275km in diameter Thick atmosphere seems to stop only small projectiles Almost no craters smaller than 10 km in diameter Counting of larger craters suggests surface age of roughly 500 million years Probable indication of persistent geological activity

15 February 2005AST 2010: Chapter 912 Volcanoes on Venus Significant volcanism Largest volcano, called Sif Mons, wider but lower than Mauna Loa in Hawaii Some volcanoes have shapes like “pancake domes” Volcanic bulges called coronae are common These are produced by hot magma from the planet’s interior which does not make it to the surface Computer-generated view of Sif Mons Pancake-dome volcanoes

15 February 2005AST 2010: Chapter 913 The Massive Atmosphere of Venus Atmosphere is 96% carbon dioxide, 3.5% nitrogen, and very little else The CO 2 traps heat on the planet via the greenhouse effect Surface temperature is more than 700 K (850°F)

15 February 2005AST 2010: Chapter 914 Birth of Venus Backward rotation of Venus may have been caused by a giant impact early in its history The massive atmosphere and high surface temperature of Venus may have been caused by runaway greenhouse effect

15 February 2005AST 2010: Chapter 915 The Geology of Mars Mars is more hospitable than Venus to humans, making Mars more interesting Early missions to Mars: 1965: Mariner 4 fly by 1971: Mariner 9 was the first to orbit 1976: Vikings 1 and 2 landed 20 years passed with 2 failed missions

15 February 2005AST 2010: Chapter 916 Spacecraft Exploration of Mars Recent missions: 1997: Pathfinder landed and Mars Global Surveyor orbited 2002: Another craft orbited 2004: 2 U.S., 1 European Space Agency, and 1 Japanese craft sent (Japanese craft failed to orbit and ESA rover, Beagle, didn’t function, but U.S. landers succeeded)

15 February 2005AST 2010: Chapter 917 Global Properties of Mars Mars’ diameter is half Earth’s A small metal core, but no magnetic field We have good maps of Mars’s surface showing: Olympus Mons: highest peak in the solar system Vallis Marineris: largest canyon in the solar system Highlands and lowlands Highlands believed to be older than lowlands Computer-generated rendering of Olympus Mons

15 February 2005AST 2010: Chapter 918 Topographic Map of Mars

15 February 2005AST 2010: Chapter 919 Volcanoes on Mars The lowland plains may have 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

15 February 2005AST 2010: Chapter 920 Martian Cracks and Canyons Valles Marineris is the largest canyon in the solar system Formed by tectonic cracking in the Tharsis bulge L.A. to N.Y. Landslides in valley are evidence of erosion (water?)

15 February 2005AST 2010: Chapter 921 Martian Polar Caps and Climate Thin atmosphere, like Earth’s 30km up Mostly CO 2 Clouds of dust, H 2 O, and CO 2 Seasonal ice caps of CO 2 (dry ice) Permanent polar caps (south) have H 2 O Ice in the soil (permafrost)

15 February 2005AST 2010: Chapter 922 Climate Change on Mars Mars suffers from 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)

15 February 2005AST 2010: Chapter 923 Life on Mars

15 February 2005AST 2010: Chapter 924 Search for Life on Mars Life as we know it needs water If Mars had had water in the past, life could have existed there Scientists have tried looking for signs of life on Mars in a variety of ways, so far with negative results It could be that UV light has sterilized the surface, but could microbes live below? Some scientists claimed that a meteorite from Mars shows possible evidence of life in its past (see next slide)

15 February 2005AST 2010: Chapter 925 Martian Meteorite