Moon

THE MOON

Highlands - heavy cratered

Mare (maria, pl.) - smooth

Mass of moon = 1/81 Earth mass

gravity of moon - 1/6 Earth gravity

Diameter of moon - 1/4 Earth diameter

Mountain ranges (formed by debris) and valleys

Ridges and high crater rims

Moon rotates on axis at same rate as its rotation
about the Earth
        Synodic Period (about 29.5 days for moon)
        As a result, same face is always toward Earth


Most locations in sunlight for 15 days (temp = 130 C)
Also in darkness for 15 days (-110 C)

July 20, 1969 - Aldrin and Armstrong walk on moon
(Apollo 11) while Collins orbits

Six moon missions total (Apollo program)

Lunar Surface:

        igneous rocks - formed by lava cooling
        few sedimentary rocks (settling)
        Thick crust (12% of total volume)

        in maria, rocks are mainly basalts
        in highlands, anorthosites (rare on earth)
        some rocks are breccias (mixtures, welded together)

        soil - bits of dust and fragments,  small glassy
globules
        NO WATER - no life.

Dating of moon done by:

        Radioactive dating of material brought back
        crater dating (which areas are most heavily cratered)

Craters with rays have formed more recently (they
formed over other areas)

General picture:

        Moon formed about 4.6 billion years ago
        top 100 km or so was molten for about 200 million
                years after

        From 4.2 to 3.9 billion years ago:

        Heavy bombardment by planetesimals
        Moon heated up from radioactive elements inside -
                volcanism  began
        lava flowed onto surface

        By 3.1 billion years ago, era of volcanism ends
        active lunar history ends (here ends similarity with
                Earth)

        No tectonics or erosion

Interior

        crust:  light material, with silica-rich mantle
        metallic (iron) core

        seismically quiet compared to earth (not totally
sure)
        minor magnetic field, frozen into lunar rocks
(possibly                       left over from old molten core)
        slow heat flow from core to surface (1/3 of earth’s)

Origin of moon theories

1.  Fission - separated from earth

2.  Capture - captured by earth

3.  Condensation - formed near and simultaneously with
earth

1 - 3 === > probably not

4.  interaction of earth with planetesimals which
formed moon

5.  ejection of ring when  earth was hit by
planetesimal