MOON, “Luna”

Mass: 0.0123 M

Radius: 0.27 R

Mean Density: 3.34 g/cm3

Gravity: 0.17 g

5th largest moon in Solar System Surface area ~ Africa

Six landings by humans (1969 – 1972)

Lunar Surface Near Side: - only side of moon visible from Earth

http://www.spacegrant.hawaii.edu/class_acts/MoonLatLong.html

Far Side or “Dark Side”:

- never seen from Earth

- completely unknown before 1959

http://www.spacegrant.hawaii.edu/class_acts/MoonLatLong.html

http://astrogeology.usgs.gov/Projects/Clementine/images/albedo.simp750.jpeg

Light colored Highlands

- elevation 2 km above average - 85% of surface - saturated with impact craters - very old surface (4.1 – 4.4 billion yrs)

Dark colored lowlands - Maria or “Seas” - below average elevation - 15 % of surface - smoother surface with fewer craters - younger than highlands (3.3 – 3.8 billion yrs old) - only found on near side of Moon

Mare Orientale

Moon formed from molten state - surface (crust) cools first - last major impacts - broke through solidified crust - fresh molten material formed maria -evidence of lava channels -> Rilles

Apollo 15

Far Side of Moon: - crust thicker - influence of Earth’s gravity no maria

Interior Structure: - Apollo experiments (seismometers) - measured weak “moonquakes” - only due to impacts and tidal forces

- No geological activity on Moon - not enough internal heat

Crust: 60 km thick on near side 100 - 150 km thick on far side

Mantle: rigid (non-plastic) region 800-900 km thick plastic (partially molten?) region 350-400 km thick

Core: small, iron-rich, solid (?) <350 km in radius Magnetic Field: - No magnetic field - although weak field in past core was originally molten now (mostly) solid

Atmosphere: - No atmosphere

- gravity is too weak to keep atm. - no volcanic activity to replace atm.

- Surface Temp ranges from 130 oC (day) to –170 oC (night) 266 oF (day) to –274 oF (night)

Formation of the Moon Unusual features about the Moon

- different density than the Earth - lack of large iron core - complete lack of water in rocks - but, some chemistry similar to Earth - orbits in ecliptic plane (not above Earth’s equator)

Four different ideas: Fission / Daughter Theory

rapidly spinning young Earth lost material -formed Moon

BUT: Earth’s rotation - not fast enough Ejecta - unstable orbits Ejecta would be aligned with Earth

Capture Theory Moon formed separately in solar system

-captured by Earth

BUT: Physics - Moon would need to lose energy to be captured, would

have very eccentric orbit Chemistry – similarity to Earth

Co-creation / Sister Theory

Earth-Moon formed as double object

BUT: Moon has diff. density (iron content) Chemistry – lack of water in rock

Giant Impact Theory

Early Earth suffered large impact -debris formed Moon

BUT: Very complicated theory, impact occurred at very specific time

Best fits observational data -Moon’s density similar to Earth’s

crust and mantle -extremely hot formation (impact) evaporates all water in material

-orbit of debris related to incoming direction of object (ecliptic plane)

-impact may have caused tilt of Earth’s axis ???