The Moon's Destruction?

[Guest Marix]

I recently watched a documentary regarding Saturn's rings. It spoke of a theory which stated the rings were possibly formed from the destruction of a moon orbitting Saturn. It caused me to wonder - theoretically, of course - what would happen if our own Moon was destroyed in some way - would Earth eventually (I presumed there would be a nuclear winter-style fallout over Earth's atmosphere for X amount of time) gain similar rings? What would the immediate and long-term effects be? Any of you care to shed light on my query?

[5614]

well it depends on how the moon was destroyed.

 

if it 'blew-up' into thousands of pieces but for some reason decided to stay almost where it started then it would form almost a ring.

 

quite why it would blow up and even if it did, surely the energy from the 'blow-up' would force it either into earth or out of earth's gravity.

[ed84c]

The moon is steadily moving away from us, and therefore unlikely to have any affects on us (due to the fact its probably going to be a long time until such an event may occur).

[ed84c]

was the programme you watched the sky at night by any chance?

[5614]

The moon is steadily moving away from us, and therefore unlikely to have any affects on us (due to the fact its probably going to be a long time until such an event may occur).

 

the moons orbital diameter is ~ 800,000 KM, it is getting 3.8cm bigger each year, this is hardly noticeable... many will just ignore it although "technically" is it getting further from us.

[Janus]

There is a natural process through which the moon could form a ring system. It is through the continued evolution of the same tidal action that is causing it to move away from the Earth as it is now.

 

As the Moon moves into a slower, higher orbit the trade off is that the Earth slows down in its rotation. Given enough time the Earth will rotate at the Same rate as the Moon revolves around it, always presenting the same face towards the Moon. This is known as tidal lock. However, the Moon is not the only actor in slowing the Earth's rotation; the Sun also has an influence, as it tries to bring the the Earth into tidal lock with itself. The result would be that once The Earth and Moon have achieved tidal lock, the Sun will continue to try and slow the Earth's rotation. The Moon will try to keep the Earth locked with itself. As a result, the Monn will transfer angular momentum from itself to the Earth, in much the manner as the Earth now transfers angular momentum to the Moon. The loss of momentum will cause the moon to fall into a lower, faster orbit. It will continue to transfer angular momentum to the Earth in an attempt to speed up the Earth to match its new orbital period, but doing so just moves it into even a lower and faster orbit. The moon will continue to spiral in until it reaches its Roche limit and is torn apart by tidal forces and forms a ring around the Earth.

 

The kicker is the phrase "given enough time". The above process takes so long that before then, our sun will expand into a red giant as a part of its evolution and very likely engulf and destroy the Earth and Moon.

[swansont]

The kicker with the larger planets is that I think it's the large gravitational forces that tear the moons apart and/or keep them from forming in the first place. Obviously with the Earth that's not happening. I'm not sure how much the moon sizes matter.

 

It's possible that if the moon were destroyed, but the mass were kept in orbit, that it might gravitationally re-coelesce to some extent.

[[Tycho?]]

The kicker with the larger planets is that I think it's the large gravitational forces that tear the moons apart and/or keep them from forming in the first place. Obviously with the Earth that's not happening. I'm not sure how much the moon sizes matter.

 

It's possible that if the moon were destroyed' date=' but the mass were kept in orbit, that it might gravitationally re-coelesce to some extent.[/quote']

 

Yeah, these are called tidal forces. Since gravity is stronger closer to the planet, the part of the moon facing the planet experiences a stronger pull of gravity than the far side does. When the object is close to a very massive body, this can be enough to pull the moon apart completely. Earth is not large enough to cause this to happen to the moon.

[Ophiolite]

I'm not sure how much the moon sizes matter.

The critical factors are the masses of satellite and planet' date=' and to some extent the density of the satellite. A satellite lacking tensile strength will be disrupted when there is a stronger gravitational attrraction on part of it from the parent planet than from the satellites own mass. The distance at which this occurs is known as the Roche Limit. A solid satellite would not be disrupted at this orbital distance.

There is a full mathematical treatment here.

http://scienceworld.wolfram.com/physics/RocheLimit.html

[Guest Marix]

I understand all of this and I'm speaking hypothetically, as the destruction of the moon would be - in this example - something like a stellar collision (i.e. a meteor rather than a gravitational fluctuation of some kind) The program - I didn't catch the title, I barely caught the discussion - argued that a similar event destroyed and fragmented a "moon" (or other sattelite) around Saturn and potentially Neptune. Would it be theoretically possible for something to fragment the Moon in such a way that it simply and literally breaks apart from the impact, (interestingly, what if it was knocked off its orbit and into Earth itself) and what would the effects be toward Earth? Could it create a ring system?

[DarthDooku]

I saw a show on the science channel about this. They said it is very possible that if Earth's moon was destroyed that it could make a set of rings similar to Saturn's. As long as the debris left over stayed within the gravitational pull of earth, the debris would orbit the Earth. Over millions of years, the rotation of the debris would cause it to flatten into a disk. Also, the theory is that the rings of Saturn are being pulled into the planet by gravity and will eventually burn up in the atmosphere and disappear.

 

As for the effects of the Earth not having a moon, i cant remember what they said. I dont remember any mention of nuclear winter, but there would definitely be chaos with the oceans. I think they said that without the moons gravity pulling on the oceans they would spill over due to Earths rotation.

[swansont]

I saw a show on the science channel about this. They said it is very possible that if Earth's moon was destroyed that it could make a set of rings similar to Saturn's. As long as the debris left over stayed within the gravitational pull of earth' date=' the debris would orbit the Earth. Over millions of years, the rotation of the debris would cause it to flatten into a disk. Also, the theory is that the rings of Saturn are being pulled into the planet by gravity and will eventually burn up in the atmosphere and disappear.

 

As for the effects of the Earth not having a moon, i cant remember what they said. I dont remember any mention of nuclear winter, but there would definitely be chaos with the oceans. I think they said that without the moons gravity pulling on the oceans they would spill over due to Earths rotation.[/quote']

 

What would prevent the debris from gravitationally coelescing into a new moon? For Saturn, AFAIK it's the large gravity that is the limiting factor.

 

Without the moon we would have much smaller tides and more wobble in our rotation.

[TheoryOfTime]

Yes, we would have more "wobble in our rotation", and I am sure we all no the dangers of that. So on top of the Earths gravity being dirupted we have the chance of being slung into the Sun (I think, correct me if I am wrong), sounds nice (Not). Well in the movie The Time Machine they show the moon blowing up, and a lot of the bits come crashing to the Earth destroying most of it. That is a good example of the dangers. What if we were pulled farther away from the Sun if the moons blows up. The Earth would have unstable climate shifts, the planet would enter a new Ice Age, just more intense then the last one.

[Ehlana]

I have a question: does the moon somehow protect the earth (besides from incoming asteroids and other space junk)? I thought I remembered hearing that the moon protects the earth some other way, but I may have been getting it confused with the protection from the magnetic field.

[Ophiolite]

Off the top of my head - benefits of having a large moon - no particular order.

 

Diverting some incoming bolides (comets or asteroids) as you suggested

Stabilisation of axial tilt: critical to relatively stable climates

Creation of large tides: more than double what we would get from the sun alone. Tides may have been instrumental in fostering the move of plants and animals onto land.

Here are two for Intelligent Design devotees:

Nicely sized to provide spectacular solar eclipses.

Conveniently close to provide a first step into space

 

And it's nice to look at.

[Mart]

Tides may have been instrumental in fostering the move of plants and animals onto land.

 

I agree. From sea to land - another aspect of asymmetry.

[j_p]

So, what would it take to blow up the moon?

 

And what would be the immediate and short-term consequences?

 

And could the moon blow up WITHOUT the earth getting hit with a lot of the debris?

[Janus]

So' date=' what would it take to blow up the moon?

 

 

[/quote']

A release of energy equal to about 1.25 x 10^29 joules.

 

That is equal to the conversion of 1.39 x 10^9 tonnes( about 1.9 X 10^-11 the mass of the moon itself) of matter to energy.

 

In terms of an asteroid collision this is the the equivalent of a body the size of Deimos (6 km) hitting at a velocity of 4% of the speed of light.

 

Or at velocities you are more likely to encounter: It would take a body of about the size of Saturn's moon Mimas (200 km radius) falling from the outer solar system and striking the moon head on (such that the objects velocity and Moon's orbital velocity are added together.)

[us.2u]

Well surely we would all drown as there would be no control of our tidal forces am I correct? or is it hearsay that the moon controls our tides?...us.2u

[Ophiolite]

The moon (and to a lesser extent the sun) causes the tides. In its absence the tides would be much reduced.

[insane_alien]

since we only have the one moon it would quickly(in astronomical trems) form into a new moon but this process would lead to some material being ejected from earth orbit and some being pulled into a collision course with earth. if the moon went then the tides would be more stable so i don't think anyone would drown because of it.

[us.2u]

You maybe correct but from the time the moon ceased to exist to the time a new moon created it's-self; I believe our Earth would be flooded or deeply frozen & we would all be dead absolutely no life whatsoever...The end caput finato...us.2u

[swansont]

You maybe correct but from the time the moon ceased to exist to the time a new moon created it's-self; I believe our Earth would be flooded or deeply frozen & we would all be dead absolutely no life whatsoever...The end caput finato...us.2u

 

On what basis do you draw that conclusion?

[us.2u]

http://www.r3clarke.fsnet.co.uk/project/tidal%20modelling%20theory.htm

[swansont]

[url']http://www.r3clarke.fsnet.co.uk/project/tidal%20modelling%20theory.htm[/url]

 

And how exactly do you get from tidal modeling to flooded, frozen and the end of all life?