14 July 2005AST 2010: Chapter 91 Venus & Mars

14 July 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

14 July 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

14 July 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

14 July 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!!

14 July 2005AST 2010: Chapter 96 Properties of Earth, Venus, and Mars

Terrestrial Planets Mercury Venus EarthMars

14 July 2005AST 2010: Chapter 98 Basic Properties Venus is similar to Earth in size, mass, and high geological activity has a thick atmosphere consisting mostly of carbon dioxide (CO 2 ) has a surface pressure almost 100 times greater than Earth’s has a very hot surface, with temperature of 730 K (over 850° F) Mars is rather small in mass and size compared to Earth may have had significant geological activity in the past has a thin atmosphere may have had a thick atmosphere and liquid water in the past which could have supported life

14 July 2005AST 2010: Chapter 99 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 To study Venusian geology, we needed to make a global study of its surface This task is made very difficult by its massive atmosphere The solution is to use a radar instrument to probe through the thick clouds More spacecraft have visited Venus than any other planet

14 July 2005AST 2010: Chapter 910 Missions to Venus 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 the extreme heat) 1970s: 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 from orbit, at a resolution of 100 m Images taken by Venera 13

14 July 2005AST 2010: Chapter 911 A Radar Map of Venus An image of Venus made by the Magellan spacecraft Colors have been added to indicate elevation Blue means low and red high

14 July 2005AST 2010: Chapter 912 Impact Craters and Surface Age of Venus Crater counting has been used to estimate the age of Venusian surface The largest crater, called Meade, is 275 km in diameter Venus’s thick atmosphere seems to stop only small projectiles Very few craters smaller than 10 km in diameter have been found The counting of larger craters suggests a surface age of roughly 500 million years This is a probable indication of persistent geological activity

14 July 2005AST 2010: Chapter 913 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

14 July 2005AST 2010: Chapter 914 Massive Atmosphere of Venus The atmospheric composition is 96% carbon dioxide (CO 2 ), 3.5% nitrogen, and very little else The CO 2 traps heat on the planet via the greenhouse effect The surface of Venus has a temperature above 700 K (850°F)

14 July 2005AST 2010: Chapter 915 Birth of Venus The 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

14 July 2005AST 2010: Chapter 916 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

14 July 2005AST 2010: Chapter 917 Spacecraft Exploration of Mars Recent missions: 1997: Pathfinder landed and Mars Global Surveyor orbited 2002: Another craft orbited 2004: 2 U.S., 1 European, and 1 Japanese craft sent European and Japanese craft failed, but U.S. landers (rovers) succeeded AnimationAnimation of rovers’ flight to Mars Pathfinder

14 July 2005AST 2010: Chapter 918 Global Properties of Mars Mars’ diameter is half Earth’s It probably has a small metal core, but no magnetic field Apparently the planet has no liquid material in its core today The Mars Global Surveyor has produced maps of the entire planet, showing Highlands and lowlands The highlands are thought to be older than lowlands Olympus Mons, the highest peak in the solar system Vallis Marineris, the largest canyon in the solar system Computer-generated rendering of Olympus Mons

14 July 2005AST 2010: Chapter 919 Topographic Maps of Mars

14 July 2005AST 2010: Chapter 920 Volcanoes on Mars The lowland plains look similar to the lunar maria This suggests that the plains may have formed 3 to 4 billion years ago The largest volcanoes are found on the Tharsis area 3 of them are shown at right Olympus Mons is the largest, larger than Mauna Loa in Hawaii

14 July 2005AST 2010: Chapter 921 Martian Cracks and Canyons Valles Marineris is the largest canyon in the solar system formed by tectonic cracking in the Tharsis bulge not by running water It extends for about 5,000 km similar to the distance from L.A. to N.Y.

14 July 2005AST 2010: Chapter 922 Martian Atmosphere and Polar Caps Its atmosphere is thin like the thin air about 30 km above the Earth’s surface composed mostly of CO 2 plus about 3% nitrogen and 2% argon Various types of clouds can form on Mars Dust clouds, raised by winds Water-ice clouds, similar to those on Earth CO 2 (dry ice) clouds Mars has seasonal polar caps made of CO 2 (dry ice) Mars also has permanent or residual polar caps composed of frozen CO 2 and water ice in the south much larger and composed of water ice in the north Liquid water on Martian surface is not possible today due to its very low pressure and temperature

14 July 2005AST 2010: Chapter 923 Climate Change on Mars Mars might have had a much thicker atmosphere and milder climate in the past The cold, dry Mars we see today may have been the result of some sort of runaway refrigerator effect The surface gravity of Mars is smaller than that of Venus or Earth Atmospheric gases on Mars can escape into space more easily than those on Venus or Earth As more and more of the gases escaped into space, the surface temperature gradually fell Eventually the planet became so cold that water froze out of the atmosphere, further reducing its ability to retain heat

14 July 2005AST 2010: Chapter 924 Channels & Gullies on Mars Geological features on Mars that appear to be evidence of water erosion in the distant and recent past have been seen: runoff channels outflow channels gullies

14 July 2005AST 2010: Chapter 925 Is There Life on Mars ? Video evidence Video evidence

14 July 2005AST 2010: Chapter 926 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 It could be that UV light has sterilized the surface, but could microbes live below? Scientists have tried looking for signs of life on Mars in a variety of ways, so far with negative results The search continues … Mars rovers’ websitewebsite