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Lecture 12

Lecture 12--14, Study Guide

6 Pages
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Department
Astronomy
Course Code
ASTA01H3
Professor
Rick Halpern

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Lecture 12: Moon and Mercury
oGeologically dead very little surface change
oMercury rotation is not locked to the Sun
o1:1 resonance is not possible because mercurys orbit is
eccentric and thus planet travel faster at perihelion
oRather Mercurys sidereal day and year are in 3:2 resonance.
Mercury rotates three times while going around the Sun twice
oMercury is best seen at its max elongation = 23.5 degrees above
horizon
oMercurys is not the hottest planet
oMercurys eccentric orbit produces hot longitudes
oInteriors
oMoons density is really low thus it does not have iron/nickel
core and no magnetic filed
oCrust is thicker than Earths
oMoon quakes occur due to meteor impact
oMercury is denser than Moon and has a weak magnetic field
oMercury has large core relative to its radius
oMercury is the densest body in the solar system when
decompressed
oEvolutionary history of the Moon
o4.6 Formation of Moon; heavy bombardment liquefies surface
o3.9 billion: Bombardment much less intense; lunar volcanism
fills maria
o3.2 billion: Volcanic activity ceases
oCurrent Theory:
Mars sized object hit the liquid Earth, caused material
www.notesolution.com
to eject to form the moon
oEvolutionary history of the Moon
oMuch less understood.
oFormed 4.6 billion years ago
oMelted due o bombardment, cooled slowly and shrank
oSurface Features
oMoon has large flat areas due to lava flow, called maria
oMaria are younger, basaltic
oHigh rocky highlands
oFar side of the moon has no maria
oMeteors hitting the moon is 10 times smaller than the crater
it produced and twice as small
oMost lunar craters 3.9 billion years old because no tectonic
forces
oRegolith: thick layer of dust left by meterorite impacts
oMoon still bombarded with micrometeorites which softens
features so some erosion due to impact of meteorite
oRegolith is 4-5 meters in maria, 3 times thicker in highlands
oLong channels in the moon suggest volcanism 3 billion years
ago
oMercury is less heavily cratered than the Moon
oScarp(cliff) several hundred of km long and 3km high
produced by shrinking surface
oCaloris Basin: a large impact feature, weird terrain on
opposite side of the planet
oLargest crater in solar system, created a weird terrain on the
opposite side due to seismic waves
www.notesolution.com

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Description
Lecture 12: Moon and Mercury o Geologically dead very little surface change o Mercury rotation is not locked to the Sun o 1:1 resonance is not possible because mercurys orbit is eccentric and thus planet travel faster at perihelion o Rather Mercurys sidereal day and year are in 3:2 resonance. Mercury rotates three times while going around the Sun twice o Mercury is best seen at its max elongation = 23.5 degrees above horizon o Mercurys is not the hottest planet o Mercurys eccentric orbit produces hot longitudes o Interiors o Moons density is really low thus it does not have ironnickel core and no magnetic filed o Crust is thicker than Earths o Moon quakes occur due to meteor impact o Mercury is denser than Moon and has a weak magnetic field o Mercury has large core relative to its radius o Mercury is the densest body in the solar system when decompressed o Evolutionary history of the Moon o 4.6 Formation of Moon; heavy bombardment liquefies surface o 3.9 billion: Bombardment much less intense; lunar volcanism fills maria o 3.2 billion: Volcanic activity ceases o Current Theory: Mars sized object hit the liquid Earth, caused material www.notesolution.com
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