Chapter 8 Contending with the Neighbors Moons Asteroids

Chapter 8. Contending with the Neighbors Moons, Asteroids, Comets, and Impact 201482177 Howon Lee

More Than Just Planets…. Our Solar System 1 Star, 8 Planets, >159 moons, ~100 Billion asteroids, >1000 billion comets Planet Moons Mercury 0 Venus 0 Earth 1! Mars 2 Jupiter 63 Saturn 53 Uranus 27 Neptune 13 Pluto 1

Lunar Puzzles • It is very large relative to its planet • Only large moon in inner solar system • It has a low density suggesting no (or minimal) core • It is depleted in siderophile elements • The moon is volatile depleted relative to Earth • Apart from volatiles, the moon looks like Earth’s mantle • The moon is younger than Earth by perhaps 50 million years

Hypotheses for Origin of the Moon • Fission hypothesis • Capture Hypothesis • Giant impact hypothesis: off-center impact between the newly formed Earth and a Mars-sized protoplanet • At a certain stage in the history of the early solar system, giant impacts were pivotal events in planetary histories • Giant impact hypothesis solves many of the puzzles about the Moon

Lunar Interior Modifications : Lunar Crust • Similarities and contrasts • Very small metallic core (about 2% of mass) • No atmosphere or ocean • Highlands vs. Maria: • Highland Crust: Plagioclase (d=2. 7 g/cm 3) • Maria: Giant Lava flows

Distinctive characeristics of lunar rocks • The lunar highlands are old and made up of anorthosite (Ca. Al 2 Si 2 O) • Mare basalts are younger, and include basalts with exceptionally high contents of Titanium • Eu is enriched in the highlands (depleted in the Mare basalts) • Eu 2+ has a valence and ionic charge similar to Ca 2+, therefore Eu substitutes readily for Ca in anorthite.

Lunar Interior Modifications : Lunar Crust • Existence of anorthositic crust with high Eu • Diversity of Mare basalts with both high and low Ti, and with depletion in Eu (Ti-poor/Ti-rich)

History of Impact in the Solar System • Impacts must have been vastly lager and more frequent in early solar system history • Late Heavy bombardment (LHB, or terminal catalysm)

Thank you http: //www. youtube. com/watch? v=dw_Y_guj. Bw. U