1. The Terrestrial Planets

2. 2 Introduction  The four terrestrial planets – Mercury, Venus, Earth (The largest), and Mars – have similar sizes and structure  These rocky worlds orbit in the inner part of the Solar System  They have very few satelites – the Earth has the relatively large Moon and Mars has two small captured asteroids as moons

3. The Terrestrial Planets3 Portraits of the Terrestrial Planets

4. The Terrestrial Planets4 Portraits of the Terrestrial Planets

5. The Terrestrial Planets5 Portraits of the Terrestrial Planets  Although the four terrestrial planets are comparable in size, they have very different atmospheres and surfaces: Mercury – smallest terrestrial planet, looks like Moon (gray, bare, cratered), essentially no atmosphere Mercury – smallest terrestrial planet, looks like Moon (gray, bare, cratered), essentially no atmosphere Venus – covered with deep sulfuric acid clouds in a dense CO 2 atmosphere, hottest planet, immense volcanic peaks tower over desolate plains Venus – covered with deep sulfuric acid clouds in a dense CO 2 atmosphere, hottest planet, immense volcanic peaks tower over desolate plains Mars – polar caps of ice and CO 2, vast red deserts with craters and dunes, canyons and dry river beds, ancient volcanoes, thin CO 2 atmosphere Mars – polar caps of ice and CO 2, vast red deserts with craters and dunes, canyons and dry river beds, ancient volcanoes, thin CO 2 atmosphere Earth – blue seas, white clouds and ice caps, red deserts, green jungles, mountains Earth – blue seas, white clouds and ice caps, red deserts, green jungles, mountains  Planetary size along with distance from Sun is the cause for these differences

6. The Terrestrial Planets6 Mercury  Introduction Mercury’s radius is 1/3 and its mass 1/20 that of Earth Mercury’s radius is 1/3 and its mass 1/20 that of Earth Circular craters cover the surface Circular craters cover the surface Congealed lava flows are found in many of Mercury’s old craters and pave much of its surface Congealed lava flows are found in many of Mercury’s old craters and pave much of its surface Enormous cliffs, formed as Mercury cooled, and shrank, wrinkling like a dried apple Enormous cliffs, formed as Mercury cooled, and shrank, wrinkling like a dried apple

7. The Terrestrial Planets7 Mercury  Mercury’s Temperature and Atmosphere Mercury’s noon temperatures at the equator (about 800° F) and nighttime temperatures (-280° F) Mercury’s noon temperatures at the equator (about 800° F) and nighttime temperatures (-280° F) These extremes result from Mercury’s proximity to the Sun and its lack of atmosphere These extremes result from Mercury’s proximity to the Sun and its lack of atmosphere Its low mass and proximity to the Sun do not allow Mercury to retain an atmosphere of any significance Its low mass and proximity to the Sun do not allow Mercury to retain an atmosphere of any significance Its lack of volcanoes suggests that Mercury never had a significant atmosphere Its lack of volcanoes suggests that Mercury never had a significant atmosphere

8. The Terrestrial Planets8 Mercury  Mercury’s Rotation Mercury spins very slowly with a rotation period of 59 Earth days Mercury spins very slowly with a rotation period of 59 Earth days Its orbit around the Sun takes 88 Earth days Its orbit around the Sun takes 88 Earth days Consequently, Mercury spins 3 times for every 2 trips around the Sun Consequently, Mercury spins 3 times for every 2 trips around the Sun Mercury’s solar day (sun to reach it's highest point in the sky twice is 176 Earth days, longer than its year! Mercury’s solar day (sun to reach it's highest point in the sky twice) is 176 Earth days, longer than its year! Because of Mercury’s slow rotation, near perihelion (when Mercury is closest to the sun) the Sun will briefly reverse direction in Mercury’s sky. Because of Mercury’s slow rotation, near perihelion (when Mercury is closest to the sun) the Sun will briefly reverse direction in Mercury’s sky.reverse direction reverse direction

9. The Terrestrial Planets9Venus  Introduction Venus has a mass and diameter very close to that of Earth Venus has a mass and diameter very close to that of Earth However, the two planets have very different surfaces and atmospheres However, the two planets have very different surfaces and atmospheres  The Atmosphere 96% CO 2, 3.5% N 2, and small amounts of H 2 O and other gases 96% CO 2, 3.5% N 2, and small amounts of H 2 O and other gases The clouds of Venus are sulfuric acid droplets with traces of water The clouds of Venus are sulfuric acid droplets with traces of water The atmosphere is extremely dense, reaching pressures about 100 times that of Earth’s The atmosphere is extremely dense, reaching pressures about 100 times that of Earth’s The lower atmosphere is very hot with temperatures of 900° F at the surface, enough to melt lead The lower atmosphere is very hot with temperatures of 900° F at the surface, enough to melt lead Spacecraft have landed on Venus, but do not survive long Spacecraft have landed on Venus, but do not survive long

10. The Terrestrial Planets10Venus  The Greenhouse Effect Large amounts of CO 2 in the atmosphere creates an extremely strong greenhouse effect Large amounts of CO 2 in the atmosphere creates an extremely strong greenhouse effect The effect is so strong Venus’ surface is hotter than Mercury’s although Venus is farther from the Sun The effect is so strong Venus’ surface is hotter than Mercury’s although Venus is farther from the Sun

11. The Terrestrial Planets11 Venus  The Surface of Venus Ground features can be mapped with radar from Earth and spacecraft orbiting Venus since radar can penetrate the clouds Ground features can be mapped with radar from Earth and spacecraft orbiting Venus since radar can penetrate the clouds Venus’s surface is less mountainous and rugged than Earth, with most of its surface low, gently rolling plains Venus’s surface is less mountainous and rugged than Earth, with most of its surface low, gently rolling plains

12. The Terrestrial Planets12 Venus  The Interior of Venus Interior of Venus probably very similar to Earth – iron core and rock mantle Interior of Venus probably very similar to Earth – iron core and rock mantle  Rotation of Venus Venus is the slowest rotating planet, taking 243 Earth days to rotate once, and its spin is retrograde (“backward”) Venus is the slowest rotating planet, taking 243 Earth days to rotate once, and its spin is retrograde (“backward”) Solar day on Venus is 117 Earth days Solar day on Venus is 117 Earth days

13. The Terrestrial Planets13 Mars  The Surface of Mars Although its diameter is ½ and its mass 1/10 that of Earth, Mars is the planet that most resembles the Earth Although its diameter is ½ and its mass 1/10 that of Earth, Mars is the planet that most resembles the Earth On a warm day, the temperature hits about 50° F On a warm day, the temperature hits about 50° F Winds sweep dust and patchy ice crystal clouds through a sky that generally is clear enough for its surface to be seen from Earth Winds sweep dust and patchy ice crystal clouds through a sky that generally is clear enough for its surface to be seen from Earth Sparkling white polar caps contrast with the reddish color of most of the planet Sparkling white polar caps contrast with the reddish color of most of the planet

14. The Terrestrial Planets14 Mars  The Surface of Mars Valles Marineris Valles Marineris A rift running along the equator stretching 1000 km long, 100 km wide, and 10 km deep A rift running along the equator stretching 1000 km long, 100 km wide, and 10 km deep This canyon, named after Mariner, dwarfs the Grand Canyon and would span the U.S. This canyon, named after Mariner, dwarfs the Grand Canyon and would span the U.S. Martian Polar Ice Caps Martian Polar Ice Caps Change in size with seasons (Mars’ tilt similar to Earth’s) Change in size with seasons (Mars’ tilt similar to Earth’s) Thin atmosphere creates more severe extremes in the seasons leading to large ice cap size variations Thin atmosphere creates more severe extremes in the seasons leading to large ice cap size variations Water contained in Mars caps is far less than that in Earth’s caps Water contained in Mars caps is far less than that in Earth’s caps

15. The Terrestrial Planets15 Valles Marineris

16. The Terrestrial Planets16 Mars  The Surface of Mars Huge channels and dry river beds Huge channels and dry river beds From winding nature of features that often contain “islands”, it is inferred that water once flowed on Mars From winding nature of features that often contain “islands”, it is inferred that water once flowed on Mars No surface liquid is now present No surface liquid is now present Huge lakes and small oceans thought to have once existed – evidence comes from smooth traces that look like old beaches around edges of craters and basins Huge lakes and small oceans thought to have once existed – evidence comes from smooth traces that look like old beaches around edges of craters and basins

17. The Terrestrial Planets17 Photo taken from Mars Rover

18. The Terrestrial Planets18 Mars  The Martian Atmosphere Clouds and wind blown dust are visible evidence that Mars has an atmosphere Clouds and wind blown dust are visible evidence that Mars has an atmosphere CO 2 (95%) with traces of N 2 (3%), oxygen and water CO 2 (95%) with traces of N 2 (3%), oxygen and water The atmosphere’s density is about 1% that of the Earth’s The atmosphere’s density is about 1% that of the Earth’s The lack of atmospheric density and Mars distance from the Sun make the planet very cold The lack of atmospheric density and Mars distance from the Sun make the planet very cold Noon temperatures at the equator reach a bit above the freezing point of water Noon temperatures at the equator reach a bit above the freezing point of water Night temperatures drop to a frigid -67° F Night temperatures drop to a frigid -67° F Thus, most water is frozen, locked up either below the surface as permafrost or in the polar caps as solid ice Thus, most water is frozen, locked up either below the surface as permafrost or in the polar caps as solid ice

19. The Terrestrial Planets19 Mars  The Martian interior Differentiated like the Earth’s interior into a crust, mantle, and iron core Differentiated like the Earth’s interior into a crust, mantle, and iron core Having a mass between that of dead Mercury and lively Earth/Venus implies Mars should be intermediate in tectonic activity Having a mass between that of dead Mercury and lively Earth/Venus implies Mars should be intermediate in tectonic activity

20. The Terrestrial Planets20 Mars  The Martian moons Phobos and Deimos are about 20 km across and are probably captured asteroids Phobos and Deimos are about 20 km across and are probably captured asteroids Their small size prevents gravity from pulling them into spherical shapes Their small size prevents gravity from pulling them into spherical shapes Both are cratered, implying bombardment by smaller objects, and Phobos has cracks suggesting an impact by an object large enough to nearly split it apart Both are cratered, implying bombardment by smaller objects, and Phobos has cracks suggesting an impact by an object large enough to nearly split it apart

21. The Terrestrial Planets21 Deimos Phobos

22. The Terrestrial Planets22 Mars  Life on Mars? Interest in life on Mars grew enormously with the misinterpretation of observations made by astronomer Giovonni Schiaparelli in 1877, who called certain straight-line features on Mars “canalli” meaning “channels Interest in life on Mars grew enormously with the misinterpretation of observations made by astronomer Giovonni Schiaparelli in 1877, who called certain straight-line features on Mars “canalli” meaning “channels English-speaking countries interpreted this as “canals” and the search for intelligent life on Mars began English-speaking countries interpreted this as “canals” and the search for intelligent life on Mars began Spacecraft photos later revealed features on Mars to be natural land structures Spacecraft photos later revealed features on Mars to be natural land structures Viking spacecraft landed on Mars to search for life up close – no evidence found Viking spacecraft landed on Mars to search for life up close – no evidence found In 1996, a meteorite was found on Earth with a Mars origin In 1996, a meteorite was found on Earth with a Mars origin Certain meteorite structures suggested Martian bacteria Certain meteorite structures suggested Martian bacteria Most scientists today are unconvinced Most scientists today are unconvinced

23. The Terrestrial Planets23 Update: Exploring Mars  Mars Pathfinder/Sojourner landed in 1997 Pathfinder studied the atmosphere and noticed wispy cirrus clouds like those on Earth and large variations in surface temperature even over distances as small as 1 meter Pathfinder studied the atmosphere and noticed wispy cirrus clouds like those on Earth and large variations in surface temperature even over distances as small as 1 meter Sojourner, a small motorized cart, examined rocks and found some indications that the landing site was once covered by water Sojourner, a small motorized cart, examined rocks and found some indications that the landing site was once covered by water  Mars Global Surveyor In Orbit in 1997 Detailed images show evidence of soil and rock layers as well as many wind-caused erosion features Detailed images show evidence of soil and rock layers as well as many wind-caused erosion features  Mars Rovers Launched June 2003 and arrived on Mars January 2004 Launched June 2003 and arrived on Mars January 2004 The rovers were designed to last for 90 days on the Martian surface. The rovers were designed to last for 90 days on the Martian surface. The rovers investigate the landscape and collect samples, sending data back to scientists on Earth.

24. The Terrestrial Planets24