moon and mercury


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moon and mercury

  1. 1. The Moon & Mercury – Dead Worlds
  2. 2. Outline <ul><li>Physical Properties & Comparisons </li></ul><ul><li>Magnetic Fields </li></ul><ul><li>Orbit Properties </li></ul><ul><li>Interiors </li></ul><ul><li>Atmospheres & Surface Conditions </li></ul><ul><li>Surface Features & Their Formation </li></ul><ul><li>Missions </li></ul>
  3. 3. Bulk Physical Properties <ul><li>Earth Moon Mercury </li></ul><ul><li>Mass 100% 1.2% 5.5% </li></ul><ul><li> 10 24 kg 5.97 0.07 0.33 </li></ul><ul><li>Radius 100% 27% 38% </li></ul><ul><li>km 6378 1738 2440 </li></ul><ul><li>Density 100% 60.7% 98.4% </li></ul><ul><li>kg/m 3 5515 3350 5427 </li></ul>
  4. 6. Magnetic Field - Moon <ul><li>The moon has no permanent global magnetic field . </li></ul><ul><ul><li>Some rocks show weak residual magnetism. </li></ul></ul><ul><ul><li>Moon’s orbit takes it through earth’s magnetotail. </li></ul></ul><ul><ul><li>Earth’s magnetic field induces a weak and transient magnetic field around the moon. </li></ul></ul>
  5. 8. Magnetic Field - Mercury <ul><li>Mercury does have a global magnetic field . </li></ul><ul><ul><li>It’s only 0.0004 times the strength of earth’s field, and is tilted 169 o to its axis of rotation. </li></ul></ul><ul><ul><li>The solar wind is 7 times more intense at Mercury’s distance, so Mercury’s magnetosphere is compressed. It only extends 1 to 1.5 diameters in front of Mercury. (Earth’s extends 8-10 diameters.) </li></ul></ul>
  6. 10. Inferences <ul><li>Small planets/moons lose internal heat more quickly than large planets, since they have less mass per unit of surface area. </li></ul><ul><li>What does the presence of a magnetic field imply about Mercury’s interior that is different than our moon’s interior? </li></ul>
  7. 11. Orbit – the Moon <ul><li>Average distance from the earth: 384,400 km (about 240,000 miles). </li></ul><ul><li>Perigee: 357,000 km. </li></ul><ul><li>Apogee: 407,000 km. </li></ul><ul><li>Orbit eccentricity: 0.0549 </li></ul><ul><li>Orbital period: 27.3 days </li></ul><ul><li>Inclination of orbit to ecliptic: 5.1 o </li></ul><ul><li>Average orbital speed: 1.0 km/s </li></ul>
  8. 13. <ul><li>The same face of the moon always faces the earth. This is synchronous rotation . </li></ul>What does this imply about the structure of the moon’s interior? Both orbital and rotational periods are 27.3 days.
  9. 14. Orbit - Mercury <ul><li>Average distance from the sun: 57.9 million km. </li></ul><ul><li>Perihelion: 46 million km </li></ul><ul><li>Aphelion: 70 million km </li></ul><ul><li>Orbit Eccentricity: 0.206 </li></ul><ul><li>Orbital Period: 88 days </li></ul><ul><li>Inclination of orbit to ecliptic: 7 o </li></ul><ul><li>Average orbital speed: 48 km/s </li></ul>
  10. 16. Resonance <ul><li>Like the moon, Mercury’s rotation is linked to its revolution, but it’s not synchronous rotation. </li></ul><ul><li>Mercury rotates 3 times for every 2 revolutions around the sun. This is resonance . It indicates a mutual, periodic gravitational influence between Mercury and the sun. </li></ul>
  11. 17. Orbital Period 88 days. Rotational Period: 59 days
  12. 18. Interior - Moon <ul><li>Clues: </li></ul><ul><ul><li>Synchronous Rotation </li></ul></ul><ul><ul><li>Low Density </li></ul></ul><ul><ul><li>Maria (basaltic flood plains) predominantly found on side facing earth. </li></ul></ul><ul><li>What inferences can you draw? </li></ul>
  13. 21. Moon’s Interior (2) <ul><li>There may be a small iron core, or a slightly larger iron-enriched rock core. </li></ul><ul><li>The interior is likely to be partially differentiated, with a transition zone between the mantle and core. </li></ul>
  14. 22. Mercury’s Interior <ul><li>Because of sulfide compounds found on Mercury’s surface, it’s likely that Mercury’s core is high in sulfides too. </li></ul><ul><ul><li>The core may be a mixture of iron and iron sulfides. </li></ul></ul><ul><li>A rather large core is needed to produce the magnetic field, despite Mercury’s very slow rotation. </li></ul>
  15. 24. Surface Conditions - Moon <ul><li>Temperature range: +250 o F to -250 o F. </li></ul><ul><li> +121 o C to -157 o C </li></ul><ul><li>Surface gravity 1.62 m/s 2 (0.16 G) </li></ul><ul><li>Albedo: 0.12 (12% of visible light is reflected. </li></ul><ul><ul><li>What happens to the other 88% of the visible light that strikes the surface? </li></ul></ul>
  16. 25. Moon’s Surface Conditions (2) <ul><li>Atmospheric pressure: 3 x 10 -12 millibar </li></ul><ul><ul><li>How could you tell from the earth that the moon has almost no atmosphere? </li></ul></ul><ul><li>Most “atmospheric” molecules are due to solar wind or ions baked out of the surface rocks by high temperatures. The “atmosphere” is best detected on the night-time side of the moon. </li></ul>
  17. 27. Surface Conditions - Mercury <ul><li>Temperature range: 450 o C on sunlit side, -170 o C on dark side. (Greatest temperature variation of any planet.) </li></ul><ul><li>Surface Gravity: 3.7 m/s 2 (0.38 G) </li></ul><ul><li>Albedo: 0.11 (slightly less reflective than the moon) </li></ul>
  18. 28. Mercury Surface Conditions (2) <ul><li>Atmospheric pressure: 1 x 10 -12 millibar </li></ul><ul><li>“ Atmosphere” composition is similar to the moon’s: Na + , K + baked out of rocks by the high temperatures, and H + and He from the solar wind. </li></ul><ul><li>Weak polar auroras should be possible. </li></ul>
  19. 29. Lunar surface features <ul><li>Craters </li></ul><ul><li>Highlands </li></ul><ul><li>Maria </li></ul><ul><li>Wrinkle ridges </li></ul><ul><li>Rilles </li></ul><ul><li>Weathering & Erosion Processes </li></ul>
  20. 30. Craters – how do they form?
  21. 31. Meteorite begins to vaporize on impact
  22. 32. It’s the expanding vapor , not the impact, that forms the crater. That’s why craters are round, even if the meteorite impacts from a low angle.
  23. 33. Crater rims are raised above the surroundings. Rebound of the rock under the impact can form a central peak. Over time, the crater walls can slump, creating terraces.
  24. 35. Some craters have rays, or a blanket of material thrown out by the impact.
  25. 36. What do the rays indicate about the age of the crater and the energy of the impact?
  26. 37. Sometimes craters are formed in long chains
  27. 39. Lunar Highlands <ul><li>The highlands are more heavily cratered than other, lower altitude regions of the moon. </li></ul><ul><li>What does this indicate, according to the “law of cratering?” </li></ul>That the highlands are older than the lower, smoother regions. They were formed 4.6 – 3.8 billion years ago.
  28. 40. What rock are the highlands made of? Anorthosite, a close relative of granite.
  29. 41. When did the cratering happen? <ul><li>Craters are still being made today, but the rate of cratering today isn’t high enough to account for all the craters on the moon. </li></ul><ul><li>In the distant past, the rate of cratering on the moon (and presumably all the other planets & moons) must have been much higher . </li></ul>
  30. 43. Lunar Maria – just big craters? <ul><li>The lunar maria are just bigger craters, formed like any other, but they have one important difference. </li></ul><ul><li>The impacts that formed them were large enough to punch cracks all the way to the moon’s still-molten mantle. </li></ul><ul><li>Over time, runny, dark, molten basalt lava moved up through the cracks to fill in the floors of the crater basins, giving a smooth, dark surface. </li></ul>
  31. 49. Mare – singular Maria - plural No plate tectonics, but mountains form at edges of maria.
  32. 50. Features on the maria <ul><li>One strange feature forms on the surface of the smooth maria: wrinkle ridges. </li></ul><ul><li>The ridges are often winding, and connect with other ridges. </li></ul><ul><li>How were they formed? </li></ul>
  33. 51. Chocolate pudding will do the same thing, if left on the countertop too long.
  34. 52. Rilles <ul><li>Rilles look remarkably like dry river beds. They’re found on the maria. </li></ul><ul><li>If there’s no water on the moon, and there never was, how did they form? </li></ul>Rilles were formed by a flowing material, but it wasn’t water – it was lava. How do we know?
  35. 54. <ul><li>River beds are narrow at high elevation, but become wider at lower elevation, as more water flows in them. </li></ul><ul><li>Rilles are wide at high elevation, but become narrower at lower elevation, as less lava flows in them. </li></ul><ul><li>Rilles often flow downhill from the edges of maria basins, carrying away lava overflows. </li></ul>
  36. 55. An active rille on earth.
  37. 56. The Apollo 15 landing was made near the famous Hadley rille.
  38. 57. Apollo 15 rover in front of Hadley rille.
  39. 58. Erosion on the moon <ul><li>Erosion does occur on the moon. But since there’s no running water, no wind, no glaciers, how does it happen? </li></ul>Two things contribute to erosion on the moon: the drastic changes in temperature, and meteorite impacts.
  40. 59. <ul><li>The hot – cold cycle causes rocks to break into smaller pieces, and can even cause slopes (crater walls) to slowly slump downhill. </li></ul><ul><li>Meteorite impacts fracture rocks into lunar soil, a fine powder that builds up at the rate of about 1 meter depth / billion years. </li></ul>
  41. 60. Recent craters have sharp walls with little slumping Inside.
  42. 61. Older craters have poorly defined walls with lots of slumping.
  43. 62. Lunar soil is very powdery, even slippery. Why would it be slippery?
  44. 63. Lunar soil is composed of tiny glass spheres and broken fragments.
  45. 64. <ul><li>The tiny spheres were made when impacts melted lunar rocks & sprayed the liquid outward. </li></ul><ul><li>Impacts can also melt larger rock fragments together. These very rough rocks are called “breccias.” </li></ul>
  46. 65. Lunar rock fragments melted into a breccia.
  47. 66. Impacts are still continuing today, but they’re mostly micro-meteorites, like this one.
  48. 67. Mercury’s Surface Features <ul><li>Similarities to moon: </li></ul><ul><ul><li>Crust is made of anorthosite </li></ul></ul><ul><ul><li>Highly cratered </li></ul></ul><ul><ul><li>Giant Impact crater: Caloris on Mercury vs. Mare Orientale on moon. </li></ul></ul><ul><ul><li>Rilles </li></ul></ul><ul><ul><li>Scarps (formed as entire planet shrunk about 3 kilometers as it cooled). </li></ul></ul>
  49. 71. antipode
  50. 73. But then again… <ul><li>Differences between Mercury & moon </li></ul><ul><ul><li>No large maria </li></ul></ul><ul><ul><li>Smooth (lightly cratered) plains </li></ul></ul><ul><ul><ul><li>resurfaced by lava flows then re-cratered </li></ul></ul></ul>
  51. 74. Missions to the Moon <ul><li>The moon is the most thoroughly studied extra-terrestrial body: </li></ul><ul><li>17 Russian Luna orbiters & landers (1959-1976) </li></ul><ul><li>5 Russian Zond orbiters (1965-70) </li></ul><ul><li>Ranger 1-9 (1961-65) took the first grainy photos of the moon’s surface for the US. </li></ul><ul><li>Surveyor (5 successful landings, 1966-68) investigated the moon’s surface. </li></ul>
  52. 75. Missions to the Moon (2) <ul><li>5 US Lunar Orbiter missions (begun in 1964) </li></ul><ul><li>6 manned Apollo missions (1969 to 1972) </li></ul><ul><ul><li>12 men have actually walked on the moon’s surface. </li></ul></ul>
  53. 77. Missions to the Moon (3) <ul><li>Clementine (mapped the moon in 12 different wavelengths from UV to IR over a 71 day period in 1994.) </li></ul><ul><li>Lunar Prospector (1998) took photographs of the moon to determine the surface geology. </li></ul>
  54. 78. Mission to Mercury <ul><li>Only 1 mission: Mariner 10, launched in 1974. </li></ul><ul><li>Made only 3 passes by Mercury in 1975. </li></ul>
  55. 80.
  56. 81.