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Ch09 inner planets
- 1. Chapter 9 The TerrestrialPlanets Copyright © McGraw-Hill Education. Permission required for reproduction or display.
- 2. The Terrestrial Planets The four terrestrial planets – Mercury, Venus, Earth, and Mars – have similar sizes and structure These rocky worlds orbit in the inner part of the Solar System, too small and too warm to have captured massive hydrogen atmospheres like the Jovian giants They have very few natural satellites – the Earth has the relatively large Moon and Mars has two small captured asteroids as moons
- 3. Terrestrial Planets: Marsand Venus Mercury – smallest terrestrial planet, looks like Moon (gray, bare, cratered), essentially no atmosphere Venus – covered with deep sulfuric acid clouds in a dense CO2 atmosphere, hottest planet, immense volcanic peaks tower over desolate plains
- 4. Terrestrial Planets: Marsand Earth Mars – polar caps of ice and CO2, vast red deserts with craters and dunes, canyons, and dry river beds, ancient volcanoes, thin CO2 atmosphere Earth – blue seas, white clouds and ice caps, red deserts, green jungles, mountains
- 5. Terrestrial Planet Overview Planetary size coupled with distance from Sun is the cause for these differences!
- 6. Mercury Mercury’s radiusis 1/3 and its mass 1/28 that of Earth Circular craters cover the surface with the largest one being Caloris Basin with a diameter of 1300 km Unlike the Moon where they are found almost exclusively in maria, congealed lava flows are found in many of Mercury’s old craters and pave much of its surface
- 7. Surface Features ofMercury Large-scale lava flows pave much of the surface There is evidence for “recent” volcanic eruptions! This was unexpected, as Mercury is very small!
- 8. Scarps Enormous scarps (cliffs),formed as Mercury cooled, and shrank, wrinkling like a dried apple Some have been found on the Moon, but they are much smaller.
- 9. Caloris Basin Largestcrater basin on Mercury 1300 km across! Odd radial cracks near the center Uplifting in the region occurred later
- 10. Chaotic Terrain “Chaoticterrain” feature opposite side of planet from Caloris Basin possibly caused by seismic waves generated by impact that created Caloris
- 11. Topographic Map ofMercury The surface of Mercury is flatter than that of the Moon. Likely due to Mercury's stronger gravitational pull and hotter interior.
- 12. Mercury’s Temperature Mercury’snoon temperature at the equator (about 710 K = 820° F) and nighttime temperature (80 K = - 320° F) are near the Solar System’s surface extremes These extremes result from Mercury’s proximity to the Sun and its lack of atmosphere
- 13. Mercury’s Atmosphere? Itslow mass and proximity to the Sun do not allow Mercury to retain an atmosphere of any significance Its proximity to the Sun suggests that Mercury never had a significant atmosphere What little atmosphere it has has seeped out through the crust, or has Solar origins.
- 14. Ice on Mercury? Presence of ice was confirmed by Messenger spacecraft Ice is located in permanently shadowed craters. Ice may have come from cometary impacts.
- 15. Mercury’s Interior Mercury’svery high average density suggests that its interior is iron- rich with only a thin rock (silicate) crust and mantle Two possible reasons for a thin silicate surface: Silicates did not condense as easily as iron in the hot inner solar nebula where Mercury formed Rocky crust was blasted off by an enormous impact
- 16. Another Large ImpactHypothesis
- 17. Mercury’s Magnetic Field 1% as strong as the Earth’s Mercury’s very weak magnetic field probably due to: Partially molten core Slow rotation rate
- 18. Mercury’s Rotation Mercuryspins very slowly with a sidereal rotation period of 58.646 Earth days, exactly 2/3 its orbital period around the Sun of 87.969 Earth days Consequently, Mercury spins 3 times for every 2 trips around the Sun
- 19. Resonance Such aratio of periods is called a resonance Mercury’s resonance is the result of the Sun’s tidal force on Mercury and its very elliptical orbit – the Sun cannot lock Mercury into a synchronous 1:1 rotation because of the high eccentricity of Mercury’s orbit. Mercury’s solar day is 176 Earth days, longer than its year! Because of Mercury’s slow rotation, near perihelion the Sun will briefly reverse direction in the Hermean sky.
- 20. Venus Venus hasa mass and diameter very close to that of Earth However, the two planets have radically different surfaces and atmospheres
- 21. The Atmosphere ofVenus Reflected spectra and spacecraft measurements show the Venusian atmosphere is 96% CO2, 3.5% N2, and small amounts of H2O and other gases
- 22. Clouds of SulfuricAcid The clouds of Venus are sulfuric acid droplets with traces of water The clouds are very high and thick, ranging from 30 km to 60 km above the surface Surface cannot be seen through clouds Some sunlight penetrates to surface and appears as tinged orange due to clouds absorbing blue wavelengths
- 23. Polar Vortex Themotion of the atmosphere is driven by the Sun’s heating near the equator, causing the gas to expand most there. Upper layers flow toward the cooler polar regions, where they sink and flow back toward the equatorial regions. This produces a huge vortex near each pole, like water running down a drain.
- 24. Atmospheric Pressure Theatmosphere is extremely dense, reaching pressures about 100 times that of Earth’s The lower atmosphere is very hot with temperatures of 750 K (900°F) at the surface, enough to melt lead Spacecraft have landed on Venus, but do not survive long
- 25. The Greenhouse Effecton Venus Large amounts of CO2 in the Venusian atmosphere create an extremely strong greenhouse effect. The effect is so strong Venus’s surface is hotter (750 K!) than Mercury’s although Venus is farther from the Sun. The high temperature and density of the atmosphere then create the high Venusian atmospheric pressure.
- 26. The Surface ofVenus Ground features can be mapped with radar from Earth and spacecraft orbiting Venus since radar can penetrate the Venusian clouds Venus’s surface is less mountainous and rugged than Earth, with most of its surface low, gently rolling plains
- 27. Ishtar and AphroditeTerra Only two major highlands, Ishtar Terra and Aphrodite Terra and about 8% of the surface, rise above the plains to form land masses similar to terrestrial continents
- 28. Surface Features Radarmaps have shown many puzzling surface features (or lack thereof) Few plate tectonic features: continental blocks, crustal rifts, trenches at plate boundaries A few distorted impact craters and crumbled mountains Volcanic landforms dominate: peaks with immense lava flows, domes of uplifted rock, long narrow faults, peculiar lumpy terrain
- 29. An active surface? Eruptions have not been seen directly, but some lava flows appear very fresh. Idunn Mons appears to have relatively recent lava flows surrounding it.
- 30. A Young Surface! These features indicate a young and active surface Venus’s original surface has been destroyed by volcanic activity The current surface is not more than 500 million years old (much younger than Earth’s) with some regions less than 10 million
- 31. Venus is notEarth’s twin! Venus still evolving into the smooth heat flow patterns found on Earth Earth rocks have more trapped water in them, making Earth rocks “runnier” than Venusian rocks and the Earth crust thinner (which will allow easier cracking of the crust into plates for tectonic movement) Interior of Venus probably very similar to Earth – iron core and rock mantle
- 32. Early Images fromVenus Pictures from the Russian Venera landers show a barren surface covered with flat, broken rocks lit by the pale orange sunlight – sampling also indicated the rocks are volcanic
- 33. The Interior ofVenus The interior of Venus is probably similar to the Earth’s, an iron core and rock mantle Water content in interior rock is much lower than on Earth, resulting in more viscous lava.
- 34. Rotation of Venus Radar measurements show Venus is the slowest rotating planet, taking 243 Earth days to rotate once, and its spin is retrograde (“backward”) Two possible causes of this slow retrograde rotation: Venus was struck shortly after its birth by a huge planetesimal Tidal forces from the Sun and perhaps Earth may have shifted its spin axis over time Solar day on Venus is 117 Earth days Venus rotates too slowly to generate a magnetic field
- 35.
- 36. Mars Although itsdiameter is 1/2 and its mass 1/10 that of Earth, Mars is the planet that most resembles the Earth Mars extensively photographed by the Mariner, Viking, and Mars Reconnaissance Orbiter, and many other spacecraft
- 37. More Like Earth On a warm day, the temperature hits about 50° F (10° C) 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
- 38. Vallis Marineris Arift running along the equator stretching 4000 km long, 100 km wide, and 7 km deep This canyon, named after Mariner, dwarfs the Grand Canyon and would span the U.S.
- 39. The Tharsis Bulge At midlatitudes, there is the huge uplands called the Tharsis bulge Dotted with volcanic peaks including Olympus Mons, which rises 25 km above its surroundings (3 times higher than Mt. Everest on Earth) • Believed formed as hot material rose from the deep interior and forced the surface upward • Scarcity of impact craters date it at no older than 250 million years • May have created gigantic Valles Marineris
- 40. Largest Mountain inthe Solar System
- 41. Southern Polar IceCap 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 Southern cap is frozen CO2 (dry ice) and its diameter varies from 5900 km in winter to 350 km in summer
- 42. Northern Polar IceCap Northern cap shrinks to about 1000 km across in summer, has a surface layer of CO2, but is primarily water ice and has separate layers indicative of climate cycles (including “ice ages”)
- 43. Dune Fields Martianpoles are bordered by immense deserts with dunes blown by winds into parallel ridges
- 44. Water on AncientMars From winding nature of features that often contain “islands”, it is inferred that water once flowed on Mars 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
- 45.
- 46. Martian Canyon Imagefrom the Mars Global Surveyor of terraced features at the bottom of a Martian canyon.
- 47. Lake Sediments Closeupimage of rock at the Opportunity landing site Possibly formed from sediment at the bottom of a salty lake or ocean
- 48.
- 49. The Curiosity Rover Curiosity reached Mars in 2012 Analyzed geology and chemistry within Gale Crater, perhaps the sire of an ancient lake. In 2015, it found layered rock, dating it to 4 Gyr ago.
- 50. The Atmosphere ofMars Clouds and wind blown dust are visible evidence that Mars has an atmosphere Spectra show the atmosphere is mainly CO2 (95%) with traces of N2 (3%), oxygen and water The atmosphere’s density is about 1% that of the Earth’s
- 51. Temperatures on Mars 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 Night temperatures drop to a frigid 218 K (-67° F) Thus, most water is frozen, locked up either below the surface as permafrost or in the polar caps as solid ice
- 52. Martian Wind Clouds,generally made of dry ice and water-ice crystals, are carried by the winds As on Earth, the winds arise from warm air that rises at the equator, moves toward the poles, and is deflected by the Coriolis effect Winds are generally gentle, but can strengthen and carry lots of dust!
- 53. Not a dropof rain… No rain falls, despite clouds Atmosphere is too cold and dry Fog seen in valleys and ground frost has been observed CO2 “snow” falls on poles during winter
- 54.
- 55. Ancient Atmosphere ofMars Dry river beds indicate liquid water flowed in Mars’s past This implies that Mars had to have a denser atmosphere (higher pressure) to prevent the fast vaporization of surface water into the atmosphere Cratering indicates that this thicker atmosphere disappeared about 3 billion years ago
- 56. Where did theatmosphere go? 2 ways Mars lost its thick atmosphere Mars was struck by a huge asteroid that blasted the atmosphere into space Mars’s low gravity coupled with low volcanic activity produced a net loss of gas molecules into space over the first 1-2 billion years of its existence, decreasing the effectiveness of the greenhouse effect to maintain a warm atmosphere
- 57. The Martian Interior 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 Numerous volcanic peaks and uplifted highlands exist Olympus Mons and other volcanoes do not show any craters on their slopes indicating they may still occasionally erupt
- 58. The Martian Moons Phobos and Deimos are about 20 km across and are probably captured asteroids Their small size prevents gravity from pulling them into spherical shapes Both are cratered, implying bombardment by smaller objects
- 59. 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 “canali” meaning “channels” 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
- 60. Martian Fossil? Vikingspacecraft landed on Mars to search for life up closer – no evidence found In 1996, a meteorite was found on Earth with a Mars origin Certain meteorite structures suggested Martian bacteria Most scientists today are unconvinced The Curiosity rover is currently searching for signs of early life.
- 61. Why Are theTerrestrial Planets So Different?
- 62. Role of Massand Radius Mass and radius affect interior temperature This in turn determines the level of tectonic activity Low-mass, small-radius planets will be cooler inside and hence less active than larger planets This relationship is in fact observed with Mercury (the least active), then Mars, then Venus/Earth
- 63. Role of InternalActivity Internal activity also affects a planet’s atmosphere since volcanic gases are the most likely source of materials Low mass Mercury and Mars will have a smaller source of age than Venus/Earth and the low surface gravity of these small planets also means they will have trouble retaining the gases they receive Mars, Venus, and Earth all probably started with CO2 atmospheres with traces of N2 and H2O, but were then modified by sunlight, tectonic activity, and, in the case of the Earth, life
- 64. Role of Sunlight Sunlight warms a planet in a manner that depends on the planet’s distance from the Sun – the closer the warmer Amount of warming depends on the amount and makeup of the atmospheric gases present Solar warming and atmospheric chemistry will also determine the structure of the atmosphere, which may “feed back” into the amount of warming that occurs For example, warmer Venus lifts water vapor to great heights in its atmosphere, whereas at cooler Earth, water condenses out at lower heights and the upper atmosphere is almost totally devoid of water
- 65. Role of WaterContent Great differences in water content of upper atmospheres of Earth and Venus has lead to a drastic difference between their atmospheres at lower levels Water at high altitudes in Venusian atmosphere is lost to photodissociation as solar ultraviolet light breaks H2O apart with the H escaping into space Venus, as a result, has lost most of its water, whereas Earth, with its water protected at lower altitudes, has not The water near Earth’s surface then makes possible many chemical reactions not found on Venus – for example, CO2 (a greenhouse gas) is removed from the atmosphere by dissolving in water
- 66. Role of BiologicalProcesses Biological processes also remove CO2 from the atmosphere Dissolved CO2 in ocean water is used by sea creatures to make shells of calcium carbonate When these creatures die, their shells fall to ocean bottom forming a sediment The sediment eventually changes to rock, thus tying up CO2 for long periods of time With CO2 so readily removed from our atmosphere, mostly N2 is left Some CO2 can be recycled back into the atmosphere by tectonic activity Green plants breaking down H2O during photosynthesis is very likely the reason Earth’s atmosphere has a high oxygen content