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Origin of the Moon


Key Terms:

Notes: (25-1)

The moon has been studied closely since the Soviets Luna mission in 1959 to the Apollo missions of the late 1960s and early 1970s.  Although the missions allowed for close up examination of the moon and its structures, the origin of the moon is still argued among a couple of theories.

  1. The moon formed from the same cloud of dust as the Earth simultaneously
  2. The moon was ejected from the Earth as it spun rapidly during development
  3. The moon was captured by Earth's gravity as it neared the Earth
  4. The moon split from the Earth as a result of a massive collision with another planet-sized object.


After formation, Earth and moon continued to grow through the impact of meteoroids which added energy and mass to their celestial bodies.  These impacts created large craters and produced lava flows that reshaped the surfaces of both the Earth and the moon.


Properties of the Moon

The moon is characterized by light areas called lunar highlands and dark areas that are the great basins and plains of the moon called lunar maria.

(www.halien.com/TAS/Gallery/ lunar/PC/moon3.jpg)

Lunar Maria






(www.windows.ucar.edu/earth/images/ lunar_scape_small.jpg)


formed from meteor impacts
consist of great basalt flows
are among the youngest rocks (3.1 - 3.8 bill. yrs.)
some of the basins have higher gravity that the outlying areas
made of denser rocks
called mascons
many have distinctive fractures that resemble valleys called rille
formed as rivers of lava flowed over the surface

See Explanation.  Clicking on the picture will download
 the highest resolution version available.

(antwrp.gsfc.nasa.gov/apod/image/ 0210/rille_apollo10_big.jpg)

Lunar Highlands

Full Moon photo(www.randomhouse.com/features/ fullmoon/art/photo08.jpg)

are lighter in color than the maria
consist of mountain ranges and many craters
are located at the edges of maria
were most likely formed as ash and lighter igneous rocks were ejected away from the center of large meteor impacts
are significantly older than the maria basins (4.2 - 4.5 bill. yrs.)


Lunar Craters and Rays

craters are formed as a result of meteor impacts
they range in size from microscopic pits to nearly 2100km wide
many have a sunburst appearance called a ray
rays are formed as material is ejected from the center of the impact
rays may indicate that the impact is relatively recent compared to craters without rays


Lunar Soil

made primarily of regolith - loose rock
range in size from sand to dust

Photo of a single footprint in the lunar soil.

(history.nasa.gov/SP-4219/ 4219-209.jpg)








Last modified: February 17, 2004