On Forming Our Moon
|October 18, 2012||Posted by News under News|
Two new papers (here and here) have just been released in Science entitled “Making the Moon from a Fast-Spinning Earth: A Giant Impact Followed by Resonant Despinning” and “Forming a Moon with an Earth-Like Composition via a Giant Impact.” For popular science press releases on the story, see New Scientist and Space.com.
As the Space.com report explains,
The moon did indeed coalesce out of tiny bits of pulverized planet blasted into space by a catastrophic collision 4.5 billion years ago, two new studies suggest.
The new research potentially plugs a big hole in the giant impact theory, long the leading explanation for the moon’s formation. Previous versions of the theory held that the moon formed primarily from pieces of a mysterious Mars-size body that slammed into a proto-Earth — but that presented a problem, because scientists know that the moon and Earth are made of the same stuff.
The two studies both explain how Earth and the moon came to be geochemical twins. However, they offer differing versions of the enormous smashup that apparently created Earth’s natural satellite, giving scientists plenty to chew on going forward.
One of the studies — by Matija Cuk of the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, Calif., and Sarah Stewart of Harvard — suggests the answer lies in Earth’s rotation rate. [Video: New Ideas About the Moon-Forming Impact]
If Earth’s day had been just two to three hours long at the time of the impact, Cuk and Stewart calculate, the planet could well have thrown off enough material to form the moon (which is 1.2 percent as massive as Earth).
This rotational speed might sound incredible, and indeed it’s close to the threshold beyond which the planet would begin to fly apart. But researchers say the early solar system was a “shooting gallery” marked by many large impacts, which could have spun planets up to enormous speeds.
Cuk and Stewart’s study, which appears online today (Oct. 17) in the journal Science, also provides a mechanism by which Earth’s rotation rate could have slowed over time.
After the collision, a gravitational interaction between Earth’s orbit around the sun and the moon’s orbit around Earth could have put the brakes on the planet’s super-spin, eventually producing a 24-hour day, the scientists determined.
The presence of our moon (and various specific properties it possesses) is essential for advanced life on earth. Remarkably, the collision between our earth and moon had to be exquisitely finely-tuned in order for advanced life on earth to be possible. Another reminder that we live in a designed universe.