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A1 07 Moon Mercury

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Prof. Miller's Astronomy 1 lecture notes on the Moon and Mercury

Prof. Miller's Astronomy 1 lecture notes on the Moon and Mercury

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  • 1. Luna LACC §8.2, 4, 5 • Know Luna’s (Earth’s Moon) interior and origin • Know Luna’s (Earth’s Moon) surface features and age • Understand the Earth-Moon system An attempt to answer the “big question”: what is out there? Are we alone? Thursday, March 4, 2010 1
  • 2. Luna: Earth’s Moon (red light) http://www.lpi.usra.edu/lunar/missions/clementine/images/ Thursday, March 4, 2010 2
  • 3. Luna: Size (red light) http://www.astronomy.org/programs/moon/moon.html Thursday, March 4, 2010 3
  • 4. Earth and Moon to Scale or 239,000 ± 13,500 miles (which amounts to 30.1 Earth diameters) http://hyperphysics.phy-astr.gsu.edu/hbase/solar/moonscale.html#c2 It took the Apollo astronauts about three days to get to the moon. Once they got their, they weighed only 1/6th what they did on Earth. E.g. if you weigh 100 lbs on hear, you’d weight 17 lbs on the moon. Thursday, March 4, 2010 4
  • 5. Earth-Moon System: Tides The Moon is the dominant tidal influence because the fractional difference in its force across the Earth is greater than the fractional difference seen from the Sun. This difference in force follows the inverse square law. http://hyperphysics.phy-astr.gsu.edu/hbase/tide.html#mstid Thursday, March 4, 2010 5
  • 6. Earth-Moon System: Tides http://astro.unl.edu/classaction/animations/lunarcycles/tidesim.html http://www.atlantickayaktours.com/Pages/ExpertCenter/navigation/Navigation-4.shtml Thursday, March 4, 2010 6
  • 7. Earth-Moon System: Moon’s Tide Locked Orbit When the Moon first formed after the Giant Impact, it was much nearer to the Earth (20,000km or 20 times nearer than present.) Both bodies exerted a pull on each other causing huge tidal forces. ...which resulted in the slowing on both the Earth’s and the Moon’s speed of rotation. The resultant imparting of angular momentum then caused the Moon to move further away. This process is still ongoing, with the Earth’s days shortening by 0.0015 milliseconds per year and the Moon moving away at about 3.8 cm a year. The Moon is no longer slowing its rotation as it is in orbital synchronicity with the Earth. That means that it takes just as long for it to rotate a full 360 degrees on its axis as it does to orbit once round the Earth. Will the Moon move so far out that it may actually leave its orbit altogether? No worries; The Sun is set to explode long before that! http://www.math.nus.edu.sg/aslaksen/gem-projects/hm/0102-1-phase/ORIENTATIONOFTHEMOON.htm Thursday, March 4, 2010 7
  • 8. The Moon has a Luna: Interior crust (C) which is around 60 km (37 miles) thick on the (red light) near side and even thicker on the far side. The mantle (B) extends down to a depth of 1000 km (620 miles). A semi-molten core (A) is probably in the centre... http://www.nmm.ac.uk/server?show=conWebDoc.8024&setPaginate=No Thursday, March 4, 2010 8
  • 9. Luna: Interior (red light) http://www.astro.psu.edu/users/niel/astro1/slideshows/class41/slides-41.html Thursday, March 4, 2010 9
  • 10. Our Moon’s Origin and Evolution http://videos.howstuffworks.com/hsw/9998-the-moon-formation-video.htm 3:32 Thursday, March 4, 2010 10
  • 11. Luna Timeline Years Ago Event 4.5 billion A Mars sized object (about 1/10th the mass of the Earth) impacts the Earth. 4.5 billion The accretion of material thrown into orbit by the impact forms the Moon. Massive impacts heat the moon resulting in differentiation, but eventually a crust forms over magma oceans. 3.8 billion Lowland basins fill with lava, forming the maria. 3.2 billion As the Moon continues to cool, volcanic activity ceases. Meteorites impacts continue--but at an ever decreasing rate--forming fresh craters and lunar regolith. (based on crater counting and radiometric dating) Thursday, March 4, 2010 11
  • 12. Lunar Impact Rate http://muller.lbl.gov/pages/crateringrates.htm Thursday, March 4, 2010 12
  • 13. Current Impact Rates http://woodahl.physics.iupui.edu/Astro100/12-25.jpg Thursday, March 4, 2010 13
  • 14. Notable Crater: Tycho http://antwrp.gsfc.nasa.gov/apod/ap050305.html Thursday, March 4, 2010 14
  • 15. Notable Crater: Tycho Copernicus (upper left) and Tycho (lower right), each with extensive ray systems of light colored debris blasted out by the crater-forming impacts. In general, ray craters are relatively young as their rays overlay the lunar terrain. In fact, at 85 kilometers wide, Tycho, with its far reaching rays, is the youngest large crater on the nearside. Crater Copernicus, surrounded by dark mare which contrast nicely with its bright rays, is 93 kilometers in diameter. http://antwrp.gsfc.nasa.gov/apod/ap050305.html Thursday, March 4, 2010 15
  • 16. Notable Crater: Tycho • The 170 km Baptistina parent body disrupted ~160 My ago in the main asteroid belt and created many fragments. • Many of the 1-10 km fragments reached a nearby resonance and escaped to the terrestrial planet region. A few hit the Earth and Moon. • These fragments likely produced the ~65 My old Chicxulub crater on Earth and the ~110 My old Tycho crater on the Moon. http://www.boulder.swri.edu/science.php Thursday, March 4, 2010 16
  • 17. Apollo Missions http://www.lpi.usra.edu/lunar/missions/apollo/ Thursday, March 4, 2010 17
  • 18. Ice (H2O) on the Moon Surface Temperature Day: 107°C (225°F) Night: 153°C (-243°F) The Moon has no atmosphere...this means [ice] will rapidly sublime directly into water vapor and escape into space.... Over the course of a lunar day (~29 Earth days), all regions of the Moon are exposed to sunlight [unless you’re] in a permanently shadowed http://www.cmf.nrl.navy.mil/clementine/ area. Thursday, March 4, 2010 18
  • 19. You on The Moon There is no atmosphere to speak of. You will be at the mercy of harmful radiation and meteorites. The temperatures are extreme: 257°F days, -283°F nights. You’ll weigh 1/6th what you do on Earth. (If you weigh 100 lbs on Earth, you’ll weigh only 17 lbs on the moon.) A “day” will take about 29.5 Earth days. If you can see the Earth, it will be 1.9° on the sky (or 3 1/2 times larger than the moon) and never change its position in the sky, but it will go through phases. It took the Apollo astronauts about three days to get to the moon. http://www.sciencedaily.com/releases/2007/02/070205130324.htm Thursday, March 4, 2010 19
  • 20. Luna LACC §8.2, 4, 5 • Know Luna’s (Earth’s Moon) interior (mantle is solid, core is unusually small) and origin (impact theory) • Know Luna’s (Earth’s Moon) surface features (highlands, maria, craters, regolith, water ice!) and age (highlands--4.4 billion, maria--3.5 billion; young crater vs old crater) • Understand the Earth-Moon system: tides, tide locked orbit An attempt to answer the “big question”: what is out there? Are we alone? Thursday, March 4, 2010 20
  • 21. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 8, pp. 192-193: 14. Due at the beginning of the next class period. Be thinking about the Solar System Project. Thursday, March 4, 2010 21
  • 22. Mercury LACC §8.2, 4, 5 • Know Mercury’s interior and origins • Know Mercury’s surface features and age • Understand the length of a Mercury day and year An attempt to answer the “big question”: what is out there? Are we alone? Thursday, March 4, 2010 22
  • 23. Mercury: A Planet of Craters This spectacular image ... was snapped [6 Oct 2008] ... about 90 minutes after MESSENGER's closest approach to Mercury, when the spacecraft was at a distance of about 27,000 kilometers (about 17,000 miles) http://science.nasa.gov/headlines/y2008/07oct_firstresults.htm Thursday, March 4, 2010 23
  • 24. Mercury: Size Earth Mercury Luna Diameter: 7926 mi 3032 mi 2160 mi 2.54 1.0 0.71 http://www.arcadiastreet.com/cgvistas/mercury_002.htm Diameter: Thursday, March 4, 2010 24
  • 25. Mercury’s Interior The metallic core extends from the center to a large fraction of the planetary radius. Radar observations show that the core or outer core is molten. Image credit: Nicolle Rager Fuller, National Science Foundation http://www.jpl.nasa.gov/news/news.cfm?release=2007-050 Thursday, March 4, 2010 25
  • 26. Mercury Timeline http://www.5min.com/Video/Learn-about-The-Formation-of- Years Ago Event the-Planet-Mercury-117568413 1:19 4.5 billion Mercury forms with an unusually large iron core, either because few lighter elements could condense so close to the sun, or because a catastrophic impact ripped away most of its mantle 4.5 billion The heat of accretion results in differentiation, but eventually Mercury cools and a crust forms. As the planet cools, it shrinks, forming scarps. Many craters still exist from this period within Mercury’s intercrater plains. 3.9 billion The smooth plains form until the crust becomes too thick for vulcanism. The rate of impacts decreases. (based on crater counting) Thursday, March 4, 2010 26
  • 27. Mercury: Intercrater Plains vs Smooth Plains Intercrater Plains w/ Old Craters Smooth Plains w/ Young Craters Which surface is older? How can you tell? http://photojournal.jpl.nasa.gov/targetFamily/Mercury?order=Mission&sort=ASC&start=200 Thursday, March 4, 2010 27
  • 28. Mercury: Scarps This scarp is about 350 km (220 mi) long and transects two craters.... The maximum height of the scarp south of the [lower] crater is about 3 kilometers. Notice the shallow older crater perched on the crest of the scarp. Ridges, Scarps, Craters http://photojournal.jpl.nasa.gov/targetFamily/Mercury?order=Mission&sort=ASC&start=200 Thursday, March 4, 2010 28
  • 29. Mercury: Caloris Basin The largest surface feature on Mercury is the Caloris Basin, which resulted from a collision with an asteroid. The basin, which is more that 1000 kilometers across, is visible as the large circular feature at the bottom of the above photograph. http://apod.nasa.gov/apod/ap960120.html Thursday, March 4, 2010 29
  • 30. Mercury: 3:2 Spin-Orbit Resonance Sidereal rotational period = 58.7 d. (sidereal day) Period of revolution = 88 d. (sidereal year) “a day” = 176 c. (solar day) 2:3 ratio, spin orbit coupling (58.7/88 = 2/3) Solar day = 3 sidereal days = 2 years http://www.csulb.edu/~gordon/LectureNotes/Mercury.html Thursday, March 4, 2010 30
  • 31. You on Mercury There is no atmosphere to speak of. You will be at the mercy of harmful radiation and meteorites. The temperatures are the most extreme in the solar system: 257°F days, -283°F nights. (Lead melts at 622°F.) The sun is 1.4° on the sky (or 3 times larger than on Earth) and appears 6.7 times brighter. A full “day” will take about 157 Earth days. You’ll weigh just over a 1/3 of what you do on Earth. (If you weigh 100 lbs on Earth, you’ll weigh only 38 lbs on Mercury.) http://www.sci-fi-o-rama.com/2008/08/06/ chesley-bonestell-the-surface-of-mercury/ Thursday, March 4, 2010 31
  • 32. Mercury LACC §8.2, 4, 5 • Know Mercury’s interior (large iron core) and origins (condensation vs impact theory) • Know Mercury’s surface features (intercrater planes, smooth planes, scarps, Caloris Basin) and age (4.5 billion years) • Understand the length of a Mercury day (solar--157 days, sidereal--59 days) and year (--88 days): spin-orbit resonance An attempt to answer the “big question”: what is out there? Are we alone? Thursday, March 4, 2010 32
  • 33. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 8, pp. 192-193: 18. • Ch 9: Tutorial Quiz accessible from: http:// www.brookscole.com/cgi-brookscole/course_products_bc.pl? fid=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due at the beginning of the next class period. Be thinking about the Solar System Project. Thursday, March 4, 2010 33