Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets...
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![Page 1: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/1.jpg)
Origin of the Moon
Origin of the Moon
7 September 20127 September 2012
![Page 2: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/2.jpg)
Why study the origin of the moon?
• How do terrestrial planets form?
• Effects of Moon on Earth?
• Pluto’s moons formed the same way?
![Page 3: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/3.jpg)
Why study the origin of the moon?
• How do terrestrial planets form?
• Effects of Moon on Earth:
• Tides
• Obliquity stabilized
![Page 4: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/4.jpg)
terrestrial planets formation
• Disk of gas and dust around Sun
• Interparticle collisions: if impact velocities are low enough, we get gravitationally bound aggregates
• 10,000 yrs: 10 km-sized bodies
• 100,000 yrs: Moon-Mars sized (~2000 km, ~20 “embryos”)
• 1 million-10 million yrs: planet-sized “giant impacts” will reduce number of embryos to 4 terrestrial planets
![Page 5: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/5.jpg)
Why giant impacts
• Planets spin faster than they orbit
• Planets are tilted to orbital revolution
![Page 6: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/6.jpg)
Moon Properties
• Name some of the distinguishing properties of the Moon…
![Page 7: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/7.jpg)
Moon Properties
1.Earth has only 1 Moon
2.Depleted in Fe and volatiles
3.Oxygen isotopes similar to Earth
4.Moon’s orbit:
• is not in Earth’s equatorial plane
• Circular
• Expanding due to tidal interaction
5.Moon has very small core (I=0.39)
![Page 8: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/8.jpg)
Moon Origin Hypotheses
• Co-accretion: Earth and Moon formed together. Like sister
• Fission: Earth spun so fast that it split off a Moon-sized chunk. Like daughter
• Capture: Earth captured an independently-formed Moon as it passed by. Like wife. THESE WERE THE 3 HYPOTHESES BEFORE APOLLO!
• Giant Impact: Mars-sized body collided with proto-Earth and excavated material eventually coalesced to form Moon
![Page 9: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/9.jpg)
Evaluate the Hypotheses
Co-accretion: Moon has little iron, volatiles.
Fission: Earth never spun fast enough
Capture: too unlikely
AFTER APOLLO WE STILL HAD THE SAME THREE POSSIBILITIES
![Page 10: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/10.jpg)
Giant Impact Stages• Earth close to final
size
• Mars-sized impactor
• both differentiated
• both formed near 1 AU
![Page 11: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/11.jpg)
Where does Iron go?
![Page 12: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/12.jpg)
Where does Iron go?•Both Fe cores stay with Earth•1 lunar mass in orbit outside Roche radius•Moon is mostly impactor material
![Page 13: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/13.jpg)
How hot is the Impact?
•heat removes volatiles from debris disk
![Page 14: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/14.jpg)
Evolution of the Protolunar disk
• Centrally condensed hot disk <a> = 2.5-3REarth
• Cooling: condensation/solidification
• Collisional spreading of disk
• Accretional growth of moonlets
• Tidal evolution of moonlets
• Collisions between moonlets yield moon
![Page 15: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/15.jpg)
the post-impact moon
• Impact: Mars-sized body collides with Earth
• Debris ejected into Earth orbit
• A. heated
• B. comes from mantle (no Fe)
• C. ~1 lunar mass = ~1% Earth mass = ~10% impactor mass
• Debris accumulates to form one large Moon, not multiple small moons… but maybe a second, smaller moon hits it later
![Page 16: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/16.jpg)
ReAccretion & the post-impact moon
• Earth spin and Moon orbit locked
• Moon orbit expands a few cm/yr
• Earth rotation slows
![Page 17: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/17.jpg)
ReAccretion & the post-impact moon
• In the past, which is a possible state of the Earth/Moon system?
•A. Moon orbits closer in, Earth’s day is 18 hours
•B. Moon orbits farther away, Earth’s day is 36 hours
•C. Moon orbits closer in, Earth day is same as now
•D. Same conditions as today
![Page 18: Origin of the Moon 7 September 2012. Why study the origin of the moon? How do terrestrial planets form? Effects of Moon on Earth? Pluto’s moons formed.](https://reader034.fdocuments.us/reader034/viewer/2022051517/56649edd5503460f94bee59a/html5/thumbnails/18.jpg)
ReAccretion & the post-impact moon
• In the past, which is a possible state of the Earth/Moon system?
•A. Moon orbits closer in, Earth’s day is 18 hours
•B. Moon orbits farther away, Earth’s day is 36 hours
•C. Moon orbits closer in, Earth day is same as now
•D. Same conditions as today