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Q: What happens on earth if the moon explodes? ( Answered,   16 Comments )
Subject: What happens on earth if the moon explodes?
Category: Science
Asked by: geebs-ga
List Price: $2.00
Posted: 29 Jun 2002 04:09 PDT
Expires: 29 Jul 2002 04:09 PDT
Question ID: 34830
The answer I am looking for is primarily in terms of environmental
ramifications, but may also include social, economic and political

To help you in your answer, you may want to consider the following

1. The size of the explosion: you may consider multiple cases such as
a large fracture, broken into a few large pieces, or shattered.
2. What happens to the pieces after the explosion? Would any of them
strike or orbit earth, hitting artificial satellites?
3. Direct gravitational effects, such as changes in the rotation or
orbit of earth.
4. Indirect gravitational effects, for example, if the length of day
or year changes, then how does that effect the environment and life on
5. Climatic and ocean changes. Direct and indirect effects.
6. Decreased moonlight.

This question is not about money. It’s about intelligence. 

Any takers? Maybe a Commenter would like to impress Google into
inviting them to be a Researcher?
Subject: Re: What happens on earth if the moon explodes?
Answered By: musashidam-ga on 19 Jul 2002 21:50 PDT
Hello geebs-ga, thanks for posting an interesting query.

As has been pointed out in the comments already posted, this question
seems to have two approaches; "What would happen to the Earth without
the Moon to affect it?" and "What would the effect be on the Earth
should the Moon suddenly explode?"

Straight Dope columnist Cecil Adams tackled this very question in a
column dated October 27th, 2000 titled "I plan to destroy the moon.
What effect would this have on the earth?"

The Straight Dope

As our physicist commentator siliconsamurai-ga mentioned below, there
are no concrete answers as to what would happen to the Earth should
the moon somehow meet an untimely demise, which Mr. Adams points out
in his column, though he singles out three likely scenarios.

1.) "Loss of the meteorite shield and resultant flaming death." As one
can see by the lunar surface, the Moon has taken more than one bullet
for the team, though how many is difficult to surmise. It should be
pointed out that the lunar surface is static, with no weather patterns
to disguise these impact craters. It's likely that the Earth suffered
a similar bombardment in its infancy, though shifting geology has
hidden most of the evidence. Loss of this so-called 'meteorite shield'
is questionable.

2.) "End of life as we know it." Adams cites a book entitled 'What If
the Moon Didn't Exist? Voyages to Earths That Might Have Been' by
Astronomer Neil Comins, in which Comins speculates that a decrease in
tidal pools created by the moon's gravitational effect would have
affected the beginnings of life on Earth. Adams goes on to point out
that this is a rather moot argument, since we're already here, but you
get the picture.

What If The Moon Didn't Exist? Voyages to Earths That Might Have Been

3.) "Orbital instability." This is a bit speculative (then again, so
is everything else about this question), but it's possible that loss
of its companion satellite would cause the Earth's orbit to "become
more elliptical, [and] its axial tilt would become wobblier due to the
influence of Jupiter, and who knows what else."

In other words, it's anyone's guess as to what the exact effects would
be on the Earth in the absence of the Moon, but those are some

As to the second part of the question, "What would the effect be on
the Earth should the Moon suddenly explode?", the first thought is the
sight of giant chunks of moon-rocks crashing into the Earth's surface.
In an article posted at NASA's Ames Research Center site entitled
'Asteroid and Comet Collisions with Earth', investigators Owen B.
Toon, Kevin Zahnle, and David Morrison point out that fragments as
small as one kilometer across would be enough to wipe out all life on
Earth. Seeing as how the Moon is 3,474 km in diameter, that's quite a
load of Moon rock to rain down on Earth.

'Asteroid and Comet Collisions with Earth'

Finally, for a final speculation as to what would happen should the
moon fall prey to cosmic disaster, I direct you to a wonderful cartoon
of the 1980's entitled 'Thundarr the Barbarian', which entertains the
very premise you suggest. The scenario predicted by this television
show is indeed quite harrowing.

"The year 1994: From out of space comes a runaway planet, hurtling
between the Earth and the Moon, unleashing cosmic destruction. Man's
civilization is
cast in ruin. 

Two thousand years later, Earth is reborn... 

A strange new world rises from the old: a world of savagery, super
science, and sorcery. But one man bursts his bonds to fight for
justice! With his companions
Ookla the Mok and Princess Ariel, he pits his strength, his courage,
and his fabulous Sunsword against the forces of evil.

He is Thundarr, the Barbarian!"

Thundarr the Barbarian

Search strategy:

"asteroid damage scale"

Hope this helps,

Request for Answer Clarification by geebs-ga on 17 Oct 2002 00:39 PDT
Thanks musashidam-ga!

I'm puzzled by the comment by npod-ga (18 July 2002) that the escape
volocity of the moon is too high for any explosion to propel
significant debris out of its gravitational pull. In other words, the
gravity on the moon would simply draw back any exploded debris before
it hit earth. This would render the Thundarr scenario moot, yes?

Clarification of Answer by musashidam-ga on 05 Feb 2003 22:25 PST
Yes, factually speaking that is correct. That is the danger inherent
in trying to apply 'science' to cartoons :)
Subject: Re: What happens on earth if the moon explodes?
From: calebu2-ga on 29 Jun 2002 11:25 PDT
This question seems a big one... but I've got no problems
brainstorming on it for a while... cos I'd like to know the answer

The most interesting part of the question seems to be "what would
happen if there wasn't a moon"... because the question of what would
happen to the "bits" would be very much like asking what happens if an
asteroid hits the earth (although if a large enough chunk of the moon
were to collide, I'm sure it could be pretty crazy - see my thoughts
on that below).

Forgetting the direct human impact for a while, the ecological effects
would be massive:

* Smaller tides
 - would screw with marine life.
 - would mess up the weather too (other factors would also cause

* Faster rotation rate of the earth (with no moon to slow it down).
 - would completely confuse plantlife and animal life... although I'm
sure it would adapt somehow.
 - Faster winds (according to the nasa site). Sounds like that could
be pretty devastating.

* no moonlight
 - will also confuse animals.

* More asteroid strikes (moon deflects some)

* Large deviations in the earth's orbit
 - Must have some effect on the heat of the sun - could lead to
scorching heat or freezing cold.
 - The tropics would no longer necessarily be the closest to the
sun... so climates could suddenly change.

I'd suspect that there is a large possibility that losing the moon
could cause pretty terminal ecological damage to the earth. It seems
that a lot of the weather stability that we enjoy comes from the
interaction of the atmosphere with the moon.

In terms of human costs, besides the weather issues (which may make
vast areas of the world inhospitible, could blow through cities with
hurricane force winds)... there would be a massive emotional effect -
whether you believe in all the "mystical" properties of the moon, you
can imagine that people are going to react differently to a night
without the moon.

As for my thought about "what would happen if 50%+ of the moon was
sent on a collision course with the earth, you'd be in pretty bad
shape, I'd think. The mass of the moon would try tearing off some of
the atmosphere as it pulled closer... I'm sure that the "death spiral"
of their orbits (it's unlikely that the moon would crash directly into
the earth, so you'd expect them to pull on each other until they
crashed into each other). When it hits, you'd be looking at
devastation on a continental level, along with the effects that an
impact into the planet's plates or oceans would have world wide
(probably more than a few earthquakes, volcanos, avalanches

The other thing that I thought about on my random rambling was what
would happen if the moon was sent into a more eccentric orbit... like
if it went in an extremely oval orbit of the earth... or orbited
around a different axis.

That could be a situation where there was less devastation, but still
a lot of quirks that would have permanent changes on life. Lots to
think about. Anyway, Google answers seems to like links from the
web... so here are some links :

What would happen if we did not have a Moon?
Subject: Re: What happens on earth if the moon explodes?
From: thx1138-ga on 29 Jun 2002 17:12 PDT
Hmmm....... and interesting question, and without rambling on too
much....I agree with pretty much calebu2-ga and his thoughts.  There
are 2 things here 1.) if there wasn't a moon (ie.from the start) and
2.) if the moon exploded
There is no reason for the moon to explode unless it gets hit by
something (very big) if the moon were to be hit by a comet and it
broke up into pieces  then it's curtains for mankind I'm afraid. 
Almost certainly one of the larger parts would hit the earth, and even
if one of the larger parts missed the amount of debris pulled into our
atmosphere by gravity would cause a nuclear winter type effect.  As
for the breakdown in social strucure, it's just a queston of
time...for a few weeks things would be survivable tinned food, bottled
water etc, but as food and clean water runs out people start to fight
for it and then the end is fairly close (for most people)

By the way, calebu2-ga said....."* Faster rotation rate of the earth
(with no moon to slow it down)."

Are you sure?? I don't think so....what force is the moon taking away
from the Earth that stops us from speeding up? I'd be very interested
to hear your thoughts.  (I just hope I'm not wrong)

Subject: Re: What happens on earth if the moon explodes?
From: ulu-ga on 29 Jun 2002 19:38 PDT
First, a minor point, if the moon was to disappear, the rate at which
earth's rotation rate is slowed due to tidal drag would be decreased. 
I think the reference to a faster spinning earth was concerning no
moon ever existing; hence, less drag over earth's history so a faster
earth.  I don't think short term, this is a significat number, judging
by the little change in leap seconds added.

There are significant difference between comparing parts of the moon
colliding and asteroid impacts.  First is size.  An asteroid of about
1 km could be devastating. The moon is 3,474 km in diameter, about 22
billion 1km pieces!
The second is speed.  They were estimating 30 km/s for killer
asteroids, but the moon is in orbit with the earth.  Picking the
escape velocity for earth (11 km/s) as a rough speed for impact of the
pieces, would reduce the total momementum.  But, the overwhelming
volume of the moon would destroy the world as we know it.

The pieces are already falling.

You might also consider this recent movie.
Subject: Re: What happens on earth if the moon explodes?
From: calebu2-ga on 01 Jul 2002 06:52 PDT
Speeds up. Slows down. All sounds plausible to me :)

I think a lot of the issues would revolve around exactly how the moon
"disappeared" rather than what happens afterwards... as I started to
say towards the end of my first comment, there are a lot of different
things that could happen.

The more I think about it, the less relevant the long run effects of
no moon are relative to the overwhelming short run effects of a
devastating explosion (i think that contradicts what I first said). If
the whole moon crashes into the earth, I'm sure it would do a lot more
damage than creating a 3473km diameter crater (after all, such a
crater would have to be *how* deep? :) My question is ignoring the
nuclear winter effects, would the atmosphere and plates survive it? on
the other side of the world from the impact? and what would such a
collision feel like? (dumb questions I know).

Second, if the moon were blasted into a different (closer or more
elliptical) orbit what would happen?

What about a more distant orbit (or completely out of orbit) - that
would fit my original answer more closely. Is there a way that it
could explode so that the gravitational side effects were only first
order (ie. the nonexistence of the moon) rather than second order
(gravitational pulls caused by large amounts of debris). Eg. if the
moon were "vaporized"?

And is there a speed of gravity? ie. how long would it take us to
notice the difference visibly and physically? (as you can see I am
hardly an science expert/crack google researcher here)

Finally, if the moon were to split into two or 3 pieces orbiting in
similar paths, how would that affect the world assuming no impacts
happened? And how long would it take before such remnants would
recollide and perhaps deflect into the earth?


P.S. I don't have a link to it (because is out of service
at the moment), but 7up had a commercial where the moon blew up... not
sure that it's relevant to the question though.
Subject: Re: What happens on earth if the moon explodes?
From: siliconsamurai-ga on 02 Jul 2002 05:59 PDT
As a physicist, this question is simply unanswerable in the current form.
Subject: Re : siliconsamurai-ga : As a physicist...
From: calebu2-ga on 02 Jul 2002 11:50 PDT
Any particular reason why it is unanswerable? (seemed a perfectly good
hypothetical question to me).

If it is because there are too many variables that have not been
defined, replace them with random numbers of your choice and answer
that question :)
Subject: Re: What happens on earth if the moon explodes?
From: thenextguy-ga on 02 Jul 2002 15:06 PDT
This is a very open-ended question, but a few things can be said about

1) You need to consider what you mean by "explosion".  Other than a
collision, I can't see how it could happen.  A collision that could
destroy the Moon would have to be a big one.  For example, it's
commonly stated that an asteroid larger than a few km (approximately
one billionth the size of the Moon - volume = radius ^ 3) would wipe
out most of the life on Earth.  Probably true, but it wouldn't break
the Earth up by a long shot.  Too many variables here.  I think it's
safe to say that if even a small piece of the Moon hit the Earth,
we're in trouble.  ("Small" meaning a piece that's only a small
fraction of the Moon's total mass - one millionth of the Moon's mass,
if it hit the Earth, would sting).

2) Pieces probably would orbit Earth, just like the pieces that make
up Saturn's rings.

3) Look for precession & nutation to answer this.

4) I can't see how day or year length would change significantly.  The
Earth would stop slowing down as fast as it is now, but that's a tiny

5) Hard to say.

6) Definitely, if the Moon's gone.

Finally, the whole Moon can't fall into the Earth as a single piece. 
Earth's tidal forces would rip the Moon apart.  You can make an
estimate about where this would happen by assuming that the Moon is
held together by its own gravity (good guess) and finding the distance
from Earth where Earth's tidal forces overwhelm that.  I get something
like 20,000 km before the big breakup.  The part that sucks about that
is that tidal forces are proportional to 1/(distance)^3, so the tides
from the Moon (already twice as strong as the Sun-induced tides) would
be about 7000 times as strong as they are now.  Not enough to destroy
the Earth, but you'd probably see high tide in St. Louis.
Subject: Re: What happens on earth if the moon explodes?
From: omnivorous-ga on 06 Jul 2002 09:43 PDT
The Washington State English exam for 10th graders this year included
an essay by a scientist recommending blowing up the moon (I'd seen a
middle-column article in the Wall Street Journal 10 years ago
recommending same).  The students were asked to critique the ideas
Subject: Re: What happens on earth if the moon explodes?
From: stockzguy-ga on 07 Jul 2002 00:25 PDT
HEY!!! Don't even want to think about an "event" like that. I like the
Earth as she is. I've read where the moon "tugs" on the crust <the
plates> and it rises and falls something like 8" a day. I like the
tides and the weather just the way the way it is now, OK, maybe a few
less Hurricanes and bad storms in Texas. The moon provides stability
and helps regulate all living things on the planet, jeeze.
Subject: Re: What happens on earth if the moon explodes?
From: gooooooooogle-ga on 12 Jul 2002 22:21 PDT
I remember watching a very interesting show about this on the
discovery channel. The biggest of the moons effect I pulled from the
program was what the moon does to stabalize the earth. Precession
occurs along a spinning bodies axis, over a period of about 25,000
years, i think, the tip of the axis of the earth does a circle. The
absence of the moon would allow the earth to precess erratically, it's
spin too would go unchecked and earth would eventually have a pole
where the equater was. I don't remmeber how long it would take to
reach that point, I remember it being a small number. I wish they'd
show it again.
Subject: Re: What happens on earth if the moon explodes?
From: geronimo-ga on 16 Jul 2002 11:46 PDT
RE: calebu2-ga

The tropics aren't warmer because of being closer to thee sun.  Ther
are warmer because of the more vertical angle of the sun.
Subject: Re: What happens on earth if the moon explodes?
From: npod-ga on 18 Jul 2002 21:38 PDT
There is an important difference between the moon being struck by
something, and the moon exploding.  If the moon exploded as a result
of internal forces, including a huge bomb being detonated on or below
its surface, its kinetic energy would change, but its momentum would
not.  In the absence of an external force its momentum must remain
constant.  It would just become a less dense version of itself
continuing in the same orbit.  I.e., if you model the moon a a point
mass, it's still got the same trajectory it ever had and it would seem
that its effect on the earth would be unchanged.  Depending on the
size of the explosion, the gravitational attraction of the pieces
could well be enough to pull them back together and all that would
have changed would be the moon's temperature.

The escape velocity of the moon is roughly 5,000 mph, which is a
higher speed than can be achieved by a single explosion.  Things
explode because heat causes gas to expand, and the practical limit of
that expansion is the speed of sound.  So if the moon exploded, it
would almost certainly fall back together without any of the pieces
reaching the earth.

As far as I can tell then, if the meen were blown up life on earth
would go on as before.

If the moon were struck by an external projectile (comet, asteroid,
etc.) the consequences would on the momentum of the projectile, and
that's anybody's guess.
Subject: Re: What happens on earth if the moon explodes?
From: einsteinemc-ga on 30 Oct 2002 19:17 PST
This goes to calebu-ga. You seem have intelligent arguments, but I
can't believe that you expect me to buy that one about the tropics
being closer to the sun. The difference in distance is insignificant.
It is the amount of sun i.e.. the angle at which the light hits any
one part of the earth is the important part. So if the tilt of the
earth was to change it really just means that the tropics would be
somewhere else, which would be a big deal, but would after a fair
number of years be unimportant.
Subject: Re: What happens on earth if the moon explodes?
From: calebu2-ga on 01 Nov 2002 09:14 PST

That's why I posted it as a comment - I was in no position to say
whether my answer was right :)

Now that you mention the lack of difference in distance, I have to
agree, the tropics argument does sound pretty weak. But hypotheses are
out there to either be proved or disproved - I think we've disproved
that one.

Besides, I'm no Einstein :)


Subject: Re: What happens on earth if the moon explodes?
From: neilzero-ga on 14 Nov 2002 10:31 PST
Since we know of no way the moon could explode, let us assume one
million equal mass pieces of moon moved outward from the center of
mass at 14400 KMPH = 4 KMPS.  In minutes gravity will reassemble the
moon much as it was. Nothing important will happen on Earth's surface.
More realistic is moderate difference in speed, direction, and size of
the million pieces. At least one very large (million cubic miles?)
will likely hit Earth's surface killing a billion humans that day, and
perhaps everyone in a few weeks from secondary effects. If the large
piece is smaller there will be social, political and economic effects
among the survivors. The ecology will be devastated much as it was 65
million years ago, even though the impact velocity would be perhaps
half. Earth would then have rings somewhat like Saturn comprised of
perhaps 10% of the moon's mass. Almost 90% of the moon's mass would
fall back to the moon in a jumble, but nearly spherical. Severeral
times the average of 4KMPS would scatter up to 95% of the moon's mass
about the solar system, but survival of any humans is unlikely, unless
the explosion was quite non-symmetrical such that it favored Earth. It
appears there is a narrow range between little damage and no
survivors.  Neil
Subject: Re: What happens on earth if the moon explodes?
From: neilzero-ga on 14 Nov 2002 12:10 PST
Tiny pieces would be produced by collision of bigger pieces, and the
artifical satellites would be damaged by even the smallest peices, but
some would likely be spared a hit, for a year or longer. Tides would
be a bit smaller after some initial storms, Earth's orbit and rotation
would likely change less than 1%, unless the explosion directed most
of the projectiles at Earth. With average scattering less than 1% of
the moon's mass would hit earth's surface, but even a millionth part
would be sufficient to do great damage.   Neil

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