Formation of our Moon

RedPlanet

Q.
According to fairly popular theory, a large body collided with the earth and the result was the formation of the moon.
I wonder therefore, why is it that our planet is volcanized while the moon is not?

I suppose this question also applies to other exta-planetary bodies: why are some volcanic and most of them not?
Like Jupiter's moon Io, higly volcanic. I understand that it's close proximity to Jupiter supposedly results in volcanism, however why not our moon then?
Or other moons of Jupiter and Saturn.

popebenny16

Yes, the collison resulted in a massive ring-type arraingement which very quicly clumped together and formed the moon. It has been very slowly moving away from the Earth ever since and is also slowing down in its orbit.

There a book called, honestly, "The Big Splat" and its in Easons, deals with how the moon was formed. I'll edit this this evenign with the author and publishers details.

RedPlanet

Cheers.
I did some online research and basically they account for the non-volcanizaton of the moon by saying that the material ejected off the early earth was mostly the outer crust which means there wasn't much heavy metals in the mix.
Of which i'm a little dubious about, tbh.

elivsvonchiaing

Hmm thought provoking! First thoughts are as a small body the moon would probably have a higher spin; Therefore, preventing fissile isotopes from settling together and generating heat at the core...

Matt Holck

The moon has no spin
We always see the same side
day or night
So when u call up that shrink in Beverly Hills

The answer is actually why is the Earth Volcanic.
There is a small amount of radio-active material with in the earth from back when the earth formed which is continously decaying. The energy released prevents the Earth's core from cooling. Because the earth's volume to surface ratio is smaller than the moon's volume to surface ratio, the heat can not escape through the Earth's surface quick enough to allow the Earth to cool.

Capt'n Midnight

Don't forget the effect of sub duncted limestone and water in the ocean floor, where plates meet, the gases in that help power volcanoes too. We've not seen any volcanos on Venus - isn't the surface very young ?

the other terresterial planets would have cooled down long ago, but they show histories of vulcanism.

the moons of the outer solar system get energy from gravitational changes and that's what powers the various volcanos from molten sulphur to liquid nitrogen.

Earth volcanos are MUCH hotter than any out there.

The impact would have melted both bodies but then the moon cooled down faster and had lower heat inputs too.

The moon has a much smaller core than the earth - most heavy metals including the radioactive ones would end up there
http://abyss.uoregon.edu/~js/images/moon_core.gif


http://www.madsci.org/posts/archives/dec97/875578875.As.r.html

ifferentiation released heat very early in the Earth’s history when the iron which forms the Earth’s core sank to the center of the Earth (the heat comes from loss of gravitational potential energy of the dense iron)
...
resent day heat flow are (very) roughly 2/3 from radioactive elements and 1/3 from leftover "primordial" heat of the Earth, including accretion and differentiation

oscarBravo

Matt Holck wrote:

The moon has no spin
We always see the same side

Doesn't that imply a 28-day spin, as opposed to no spin?

elivsvonchiaing

oscarBravo wrote:

Doesn't that imply a 28-day spin, as opposed to no spin?

Relative to which object exactly?

Don't want to seem pompous but - if you think about it - its movement has to relate to another object!

Matt Holck

Actually angular momentum is an added energy contained with in the object

If the sun were to disappear with its gravitaional well,
the earth's orbit would tagent too a strraight line but the earth would keep spinning.
If the earth were to disappear with its gravitaional well,
the moon's orbit would tagent too a straight line but the moon would not spin.

Tar.Aldarion

Of course the moon rotates, it's just at the the same speed as it orbits the Earth. It takes around 27.3 days for the Moon to go around Earth so in that time, the Moon spins about its axis one revolution. So we always see the same side of the Moon.

Seanie M

Matt Holck wrote:

The moon has no spin

It does - 27.3 days. It just so happens that 1 lunar 'day' coincides with the time taken to orbit earth, thus resulting in the 1 face constantly being turned towards Earth.

1 lunar 'day' = 27.3 Earth days
1 lunar cycle, or lunar calendar month = 27.3 Earth days in terms of watching the phases complete a cycle (always rounded to 28 in general terms)


Seanie.

Tar.Aldarion

One post up man, w00t.

Seanie M

Tar.Aldarion wrote:

One post up man, w00t.

Oops! Didn't cop that at the time!

elivsvonchiaing

Why does the moon match the earth - so the spin keeps a darkside?
Is it coincidence or a 200 m/y/o feedback system no-one fully understands?

Hal1

wee like teh m000n, but nat as much as a sp00n,casue a sp00n for eatin soup sorry i had to add that

elivsvonchiaing

The moons orbit dictates the period of its orbital rotation around the Earth.

Is its own rotation settled to "somewhat" sync through the effects of general relativity (over a billion years or so) or is it coincidence?

Capt'n Midnight

elivsvonchiaing wrote:

The moons orbit dictates the period of its orbital rotation around the Earth.

Is its own rotation settled to "somewhat" sync through the effects of general relativity (over a billion years or so) or is it coincidence?

later on the earth will lock to the moon - but that's a long time away

SonOfPerdition

elivsvonchiaing wrote:

The moons orbit dictates the period of its orbital rotation around the Earth.

Is its own rotation settled to "somewhat" sync through the effects of general relativity (over a billion years or so) or is it coincidence?

have a read of this ..
http://www.wonderquest.com/MoonSpin.htm

oscarBravo

Very informative, cool.