Giant Impact Puts Moon In A Twist
spacedaily.com
The moon's orbit can be traced backwards in time to reveal that when the moon formed near the Earth, its orbit was inclined by approximately 10 degrees relative to the Earth's equator. Most other planetary satellites in the solar system have orbital inclinations smaller than 1 or 2 degrees. The cause of the moon's large orbital tilt has long been a mystery.
Relative to the ecliptic plane, the Moon's orbit is inclined about 5.1°, the Earth's equatorial plane about 23.5° (wobbles ~22-25°). Therefore, the tilt currently varies in the range 23.5±5.1°, i.e. from a minimum of approximately 18.4° to a maximum of 28.6°, as the axis of the lunar orbit precesses about the Earth's spin axis with a period of about eighteen and a half years. So, even using the minimum value in its cycle, the tilt is now almost twice as great as when the moon formed, if the initial value of 10° is good.
Article "Big Bang, New Moon" by Dr. Canup, on giant impact theory of formation:
swri.org
She briefly mentions the finding by Dr. Ward that the Moon acts to stabilize the tilt of the Earth's rotational axis, which would otherwise vary wildly, likely causing extreme climatic changes that would make the planet uninhabitable.
More on spin axis variation:
spacedaily.com
spacedaily.com
The Nine Planets - A Multimedia Tour of the Solar System / The Moon:
seds.lpl.arizona.edu
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