Earth’s Moon

1. Earth’s Moon Luna, Lune, Mond or Selene

2. Lunar Statistics • Diameter – 1,737.5km 0.27 X Earth (12,756km) • Density – 3.34 g/cm³ (0.6 Earth's density) • Orbit – 383,400km (ave. dist. from Earth 238,328mi) • Orbital Period and length of day– 27.32 • Always keeps same face toward Earth • ~18% additional surface visible due to libration and orbital inclination • 1.5” increase in distance from Earth/yr • Axial tilt – 6.7 degrees • Orbital inclination - 5.16 degrees • Gravity – 0.17 • Surface temperature • Mean –4Fo • Extremes – 225Fo : -243Fo

3. Stats (cont’d) • Atmosphere – none • Billions of years of embedded ions from the Solar Wind (provided valuable information for SW studies through return samples) • Magnetic Field – none • Remnant magnetism in some volcanic rocks suggesting an early magnetic field • Surface Features – • Regolith – • Fine-course particles mantling surface • Formed by continuous bombardment of meteorites • Mare (young) • 16% of surface area • Huge impact craters • Flooded floors by volcanic lava flows • Concentrated on Lunar near-side • Cratered Highlands (old) • Heavily cratered terrain • South Pole-Aitken (far side) 2250 km diam. & 12 km deep making it the largest impact basin on Moon • Orientale (western limb as seen from Earth) which is a good example of a multi-ring crater.

4. Near Side of Moon • Two-fold age of surface • Two phases of impact bombardment • Early large basins • Later smaller impacts • Highlands • Older crust • Heavily cratered • Formed during cooling of “magmatic ocean” • Volcanic features • Cones, flows and rilles • Mare • Younger mantled crust • Large, dark, flow filled impact basins • Far more numerous on near side • Due to asymmetric tidal (gravitational) pull of Earth • Craters • Far side more heavily cratered • Heavy Bombardment Period 3.9-3.80bya • Large multi-ring basins and mare • Bright rayed craters are smaller and stratigraphically younger

5. Far Side of Moon • Note small areal extent of mare compared to near side

6. Lunar Rocks • > 800lbs of lunar rock returned by Apollo astronauts • Vesicular basalt • 4.0-2.0bya • Most 3.8-3.2bya • Other mafic classes similar to Earth’s mantle in composition • No Water • Results in smaller family of minerals • ~100 as opposed to >2,000 on Earth • Kept at Johnson Space Center in Houston

7. Neil Armstrong’s first footprint • No atmosphere • No water or erosion • Will last until plowed under by multiple impacts

8. The Moon’s Origin • Three main theories until 1970’s (Apollo samples disproved all three) • Co-accretion • Formed contemporaneously w/proto Earth from the collapsing stellar nebula • Composition would mimic that of Earth • Fission • Split off from the Earth • Elemental ratio’s would match • Capture • Formed elsewhere in the SS and was subsequently captured by the Earth gravitational field • Difficult to reconcile Earth’s gravitational field capturing such a large object

9. The Moon’s Origin • What other explanation could account for the Earth’s Moon? • Research alternate theories for next class

10. Lunar Effects • Night light changes • Tidal changes • Stabilize Earth’s rotational wobble • Moves Earth through it’s orbit • Biological effects • Human body temp, urine composition and drug sensitivity show daily rhythmic changes

11. Earth/Moon Orbital Reference

12. Lunar Phases

13. Moon’s Tidal Pull • Creates bulge’s on opposite sides of the Earth • Lakes • Atmosphere • Crustal rocks • Spring vs neap tides • Rotational influences • Spin-orbit locking

14. Lunar Eclipses • 3 types of lunar eclipses • Total • Partial • Penumbral • 2 parts to the Earth's shadow • Penumbra • Outer part of the shadow where sunlight is not completely blocked • Umbra • Umbra is the actual shadow created by the Earth

15. Totality • Occurs when Moon is completely within umbra • Earth’s gravity and atmosphere bend and scatter shorter wavelength light • Longer wavelength light reached Moon giving it a copper or reddish glow

16. Lunar Orbit • Moon's orbit is inclined about 5 degrees to the Earth's orbit (ecliptic) • Moon passes through the ecliptic only twice a month at a pair of points called the nodes • Otherwise the Moon is either above or below the plane of the Earth's orbit and does not pass directly through the Earth's shadow • Sun tries to flatten the Moon's orbit so that it is on the ecliptic • As a result the Moon "wobbles" on its' axis • The effect is to make the line of nodes of the Moon's orbit move over time • 18.6 years to make a complete cycle • This 18.6 year sequence of eclipses is called the saros cycle • During this cycle solar and lunar eclipses occur about every six months • The exact dates of the eclipses change and do not repeat for that 18.6 year cycle

17. Eclipse Facts • Lunar eclipses only occur during a full moon • Solar eclipses only occur during a new moon • A Solar eclipse always occurs two weeks before or after a lunar eclipse • Eclipses very often occur in threes, alternating lunar, solar and lunar • The maximum time a lunar eclipse can last is 3 hrs and 40 mins • The longest time the Moon can stay in totality is 1 hr 40 mins • The maximum time for a total solar eclipse is 7 mins and 40 secs • The maximum time for an annular solar eclipse is 12 mins 24 secs • Lunar eclipses can occur up to 3 times a yr • Solar eclipses can occur at least 2 and no more than 5 times a yr • Lunar eclipses are visible over an entire hemisphere • Solar eclipses are visible in a narrow path a maximum of 167 mi wide (269km.) • At any geographic position on the Earth, a total solar eclipse occurs an average of once every 360 years • The cycle of eclipses repeats every 18.6 years called the saros • The eclipse shadow moves at 2,000 mph at the Earth's poles and 1,000 mph at the Earth's equator

18. The Moon’s Origin (cont’d)Apollo Changes the Game • Lunar rocks discount all the theories • Rocks grossly similar in composition to the Earth's mantle • Oxygen isotopic ratios are identical to Earth's • Lunar rocks are slightly enriched in refractory elements • Lunar rocks are strongly depleted in volatiles • New theory of the Moon's origin • Early solar system 4.5 bya more violent place than had been previously assumed • Accreting matter would form embryonic planets with a large range of sizes in closely spaced orbits • Final stages of planetary formation would involve the coalescence of often rather large bodies (protoplanets), punctuating this era with giant impacts in which bodies of comparable size crashed into one another at high speed • Explains wide variations among inner planets • Orbital inclinations • Eccentricities • Rotational periods • Spin axis

19. Impact Origin(0 seconds) • These computer-generated images illustrate the first 30 minutes after a Mars-size protoplanet collides with the protoearth with a velocity upon contact of 8 km/sec • Each of the four images is separated by about 400 seconds. The metallic cores of the projectile and target are shown in red and pink and their dunite mantles are shown in brown and green, respectively. • The vapor plume of mixed projectile and target mantle material is well developed in the second and third frames. This plume eventually condenses into dust, some of which remains in orbit to later accrete into a proto-moon with an initial orbital radius of about 10 earth radii • 63,780km • 384,400km average dist. today • These images are the result of a 3-dimensional hydrocode computation using the CTH code at Sandia National Laboratories.

20. Impact Origin(403 seconds)

21. Impact Origin(804 Seconds)

22. Impact Origin(1204 seconds)

23. Impact Origin(1604 seconds)

24. Impact Origin(2004 seconds)

25. Earth/Protoplanet Collision • Earth – protoplanet impact sequence • Impact generates hot, melted debris cloud or torus around Earth • Cloud cools and begins to accrete