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Lecture 12

Lecture 12--14, Study Guide

Course Code
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
oMercurys is not the hottest planet
oMercurys eccentric orbit produces hot longitudes
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
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
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
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
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
Lecture 13: Venus
oSoviet Mission more successful
oGreatest Elongation (max separation of venus and Sun as seen by
earth) = 42 degrees
oBrightest at 39 degrees, brightest after Sun and Moon
oOrbital Period 225 days
oRotation Period: 243 days retrograde
oSynodic Period: 584 days (synodic is time for venus to lap earth once
i.e Venus Sun Earth Alognment)
oRotation Rate:
oRetrograde motion: Venusian solar day is shorter than
sidereal day
2 solar Days per year
117 Earth days to get 1 venusian solar day
It takes 243 days to rotate 360 degrees
225 days in one ear
Almost circular
oAtmosphere: Dense and thick clouds, impossible to see
Surface temperature is about 730K hotter than
mercury, whole planet is hot unlike mercury due to
Solid cloud bank 50km 70km above surface
Atmosphere is mostly CO2, clouds are sulfuric acid
93 times the mass of the Earth atmosphere
92 times the pressure