Could the moon be broken ?

[astromark]

No, not a science fiction question. In reality, what if.. a large enough to break the sphere impacted the moon.? with sufficient velocity to be so energetic as to actually blow a hole so large as to destroy the integrity of the moon. I have spent many hours looking ( playing ) at Earth impactors... The moon has just come into view and so.... ?
What would happen ? Other than a beautiful display of a exploding moon, throwing a plume of debris several lunar diameters from her... would it be catastrophic for all humanity ? I think so. But a lesser scale event would have a lesser degree of destructive force. Is it all impact energy related ? Lots of questions here but consider it all please... Mark the inquisitive astronomical gnome.

[mugaliens]

No, not a science fiction question. In reality, what if.. a large enough to break the sphere impacted the moon.? with sufficient velocity to be so energetic as to actually blow a hole so large as to destroy the integrity of the moon.

Seismographs have shown that the Moon "rings like a bell." That is, it's solid and well connected enough that sound waves travel through it, around it, and that it takes a long time to stop ringing. I suspect, therefore, that all parts are sufficiently connected, "welded" I suppose is a good word, than any such impact would fracture the structural integrity of the Moon.


Other than a beautiful display of a exploding moon, throwing a plume of debris several lunar diameters from her... would it be catastrophic for all humanity ? I think so.

You bring up a wonderful point - many extinction events are tied to asteroids which impacted the Earth, but how many have been tied to Lunar ones?

[NatureTalk]

You bring up a wonderful point - many extinction events are tied to asteroids which impacted the Earth, but how many have been tied to Lunar ones?

Yes, it is an interesting question, thanks. I wonder if the folks tracking near earth objects are also tracking near moon objects?

[DarkHorse220]

Are you talking about just a really big hit that kicks up a lot of debris, or something hitting it hard enough to actually fragment it and scatter the mass to a significant degree? I can't really tell which you're getting at.

The former's going to be dependent on how much of the Moon's mass actually gets displaced. In the latter case, well, I wouldn't want to be living on Earth when that happened.

[clacton0]

Would there be loads of tidal waves if the moon broke?
And how long would it take for this to happen after the moon broke.

[Nowhere Man]

For a novel along this theme, look for Moonfall by Jack McDevitt.

Fred

[WayneFrancis]

Actually you'd be hard pressed to get anything large enough to break apart the moon. If there where something I'd be more worried about what it would do to earth. For instance it would take the same amount of energy the sun produces in almost a week to destroy the earth. The impact of the moon being destroyed on the earth is largely dependant on the direction of the impactor. It would pretty much take a object a fair size of the moon traveling at very high relative speed of the moon to destroy the moon.

If you took the moon out of the system tides would be the least of your problem. Hell the tides wouldn't even be that big of a deal. The moon stablizing the Earth's rotation would be the bigger problem.

[Jeff Root]

This was just discussed here a few months ago, and I think you may
have even contributed to the thread, Mark.

Edit: Come to think of it, I might be thinking of the thread where
someone linked to a painting of the Earth being torpedoed by a
neutron star or the like, while an astronaut on the Moon watches.

-- Jeff, in Minneapolis

[astromark]

I am amazed that Darkhorse asks what I meant,? Read post one again... While the other responses are good and yes I do remember that post Jeff. Understand that the mass is still there and tidal upheaval may not be an issue. The mass of the moon is still there so orbital stability would be insured. Debris entering Earths atmosphere would be problematic. Can we age the larger impactors on the moon to events here.? Its an interesting angle I want to explore.

[DarkHorse220]

I am amazed that Darkhorse asks what I meant,? Read post one again...

You wrote:


In reality, what if.. a large enough to break the sphere impacted the moon.? with sufficient velocity to be so energetic as to actually blow a hole so large as to destroy the integrity of the moon.

Cracking a glass sphere with a tap of a hammer results in different effects than smashing that sphere on the floor with a hard throw, so I didn't think it was unreasonable to ask for clarification on how hard of a hit you were talking about.

If there's large mass-scattering, then Earth is in trouble. If it just crumbles into dust and rocks, but there's not enough energy imparted to overcome GBE (so the Moon won't really lose any mass) then there's probably not going to be any issues.

[astromark]

Thank you Darkhorse... Um... well, Errr... and it looks like you knew all along anyway... as you so rightly noted... its just a broad question of what if's... most of which has been answered...
Magnificently spectacular plum of brightly lit debris fanning out from the moon or possibly even a broken mass of rubble. With subsequent issues from the impact of some and obvious disruption of the stability we have all become accustomed to, or maybe not. It might not be as bad for humanity as had at first thought. So the next question is... How big, how fast, what mass would puncture the moon on impact as to disrupt its integrity. That question I do not expect to be answered... its all getting a little to science fiction like for me. I will move on....

[mugaliens]

How big, how fast, what mass would puncture the moon on impact as to disrupt its integrity. That question I do not expect to be answered...

I think some reasonable assumptions can be made, as we do understand the structure of rock well enough to calculate with good precision how much dynamite is required to fracture the rock to a given depth from the borehole. Similarly, experiments with nukes have given us detailed data on larger MT explosions. Given those, detailed studies on locations such as Meteor Crater (Barringer's), and others, we have a pretty good idea of the range of impacts (mass and velocity ranges) that would be required to "break" the Moon, and by that, I assume he means "fractured all the way through."

We might be suprised to discover that it is suprisingly small, particularly if the Moon is totally solid, as we think it is. Calculating the peak sheer stress required for fracture, the energy dissipated during fracture, integrated throughout the volume of the Moon, along known peak pressure wave propogation paths, should give us the impact energy required to accomplish that.

Is there a geologist in the house?

[chornedsnorkack]

What do you think could collide with the Moon?

The outcome, and the distribution of debris, might be very different depending on whether the impactor is relatively small and very fast (70+ km/s) or big and slow (2400 m/s, or even less).

For low speed impacts, Roche limit needs considering, too.

[mugaliens]

What do you think could collide with the Moon?

Well, let's see...

Asteroid, meteor, comet, mishappen lunar lander, shrapnel from collisions involving man-made satellites, light, solar wind, cosmic dust, an exceedingly small percentage of neutrinos...

I think that about sums it up.


The outcome, and the distribution of debris, might be very different depending on whether the impactor is relatively small and very fast (70+ km/s) or big and slow (2400 m/s, or even less).

To some extent, yes. When you're talking about a body that's 3,500 km across, however, anything less than 35 km is essentially a point impact. Thus, the principle issue is one of KE.

The secondary issue, however, does involve the velocity of the impactor, for when the velocity of the impactor exceeds the velocity of sound through the medium (Lunar crust) being impacted (or the impactor) then you get a significantly different sound pressure wave from the impact. At and beyond the speed of sound, the pressure wave induced in the Moon will be transient, that is, a sonic boom. Sound travels through brick at around 3.6 km/s. In glass, it's between 4 and 5.5 km/s. In granite, it's closer to 6. Marble, not so much - back down to 3.8 km/s. Thus, if the impactor hits the Moon at less than, say, 3.5 km/s, you're definately going to have a slope to the leading edge of the sound wave the impactor makes going through the Moon.

But if it's above 6 km/s, you'll have a Lunar sonic boom.

Now, just because it's a sonic boom doesn't mean it'll fracture rock. The energy contained in a sound wave is proportional to the area under the pressure/time plot of the wave. A sonic boom has a nearly verticle rise, but only to a point. It's that peak pressure we're concerned about, though, as that will determine whether or not the rock fractures, or if it breaks the adhesion between previously independant rocks. As each fracture is created, or each adhesion broken, the energy it takes to do that reduces the peak pressure of the wavefront. Similarly, as the sound from the impact propogates, the peak pressure is also reduced.

Thus, the impactor will almost certainly "break" the moon at the point of impact. But some distance away, where the peak pressure has been reduced to the point where it is no longer sufficient to fracture rock, it ceases breaking the Moon. The question then becomes, "how much energy must there be in the impactor to continue this fracturing process throughout the Moon?"

As previously mentioned, given what we know of geology, that's not that difficult a figure to estimate (but I'm not a geologist, nor am I a mining excavations expert).


For low speed impacts, Roche limit needs considering, too.

While that holds for larger, rocky bodies, the tensile strength of most iron meteorites renders this point mute. Even larger, rocky bodies have a tensile strength which I believe is sufficient to withstand the weak Lunar gravity.

[chornedsnorkack]

Well, let's see...

The secondary issue, however, does involve the velocity of the impactor, for when the velocity of the impactor exceeds the velocity of sound through the medium (Lunar crust) being impacted (or the impactor) then you get a significantly different sound pressure wave from the impact. At and beyond the speed of sound, the pressure wave induced in the Moon will be transient, that is, a sonic boom. Sound travels through brick at around 3.6 km/s. In glass, it's between 4 and 5.5 km/s. In granite, it's closer to 6. Marble, not so much - back down to 3.8 km/s. Thus, if the impactor hits the Moon at less than, say, 3.5 km/s, you're definately going to have a slope to the leading edge of the sound wave the impactor makes going through the Moon.

But if it's above 6 km/s, you'll have a Lunar sonic boom.

Now, just because it's a sonic boom doesn't mean it'll fracture rock.
What is the speed of compression waves in the Moon? And what is the speed of transverse waves?

The energy contained in a sound wave is proportional to the area under the pressure/time plot of the wave. A sonic boom has a nearly verticle rise, but only to a point. It's that peak pressure we're concerned about, though, as that will determine whether or not the rock fractures, or if it breaks the adhesion between previously independant rocks. As each fracture is created, or each adhesion broken, the energy it takes to do that reduces the peak pressure of the wavefront. Similarly, as the sound from the impact propogates, the peak pressure is also reduced.

Thus, the impactor will almost certainly "break" the moon at the point of impact. But some distance away, where the peak pressure has been reduced to the point where it is no longer sufficient to fracture rock, it ceases breaking the Moon.
The shock is also weakened by spreading. BUT the waves are focused again into the antipodal point.

Does the interior of Moon undergo brittle or ductile failure?


While that holds for larger, rocky bodies, the tensile strength of most iron meteorites renders this point mute. Even larger, rocky bodies have a tensile strength which I believe is sufficient to withstand the weak Lunar gravity.

How big iron bodies can stay together near surface of Moon?

[astromark]

;)------- there go's mark the astronomical gnome, not wanting to be a lepricorn...;) March the 17th.

You can quickly see why I ran off---- using the Earth impactor programs that are available on line. You get some frightening information about the sort of damage a high velocity impactor can do. The poor old moon is a prime target for any passing space rock or comet. The history of such litter it surface now. Every one of those creators would have looked impressive in formation.

[mugaliens]

What is the speed of compression waves in the Moon?

Well, I don't know! Which is why I found the speed of sound through similar materials of brick, glass, granite, and marble, coming up with a range from 3.5 to 6 km/s for the velocity of the sound waves.


And what is the speed of transverse waves?

Slower than that of the P-waves.


The shock is also weakened by spreading.

I mentioned that...


BUT the waves are focused again into the antipodal point.

Not so much (http://en.wikipedia.org/wiki/File:Earthquake_wave_shadow_zone.svg). It's the Earth, but you can see how even without Earth's molten outer core, the P-waves don't reflect back to the antipodal point. S-waves are wrongly termed "surface" waves. They're secondary waves, as they arrive after the P-wave (primary). Furthermore, they're body waves, moving through the body, unlike surface waves. S-waves are the destructive ones for Earthquakes, to be sure! But not for meteor impacts.


Does the interior of Moon undergo brittle or ductile failure?

The Moon's rotation does vary slightly over time, which lends credence to the idea that at least part of it's mostly iron core is molten. Thus, no fracture there. The rest of the Moon's composition is roughly crystalline in nature, of solidified crystalline minerals, with a mafic mantle and a plagioclase-rich crust that fractures along two distinct cleavage planes.

Therefore, brittle fracture.


How big iron bodies can stay together near surface of Moon?

Are you asking "how can big iron bodies stay..."?

How do big boulders stay together near the surface of the Earth? How can they roll downhill without flying apart?

Tensile strength.

The roche limit directly applies to a large body of aggregate material. For solid objects, however, such as nearly all meteors and most asteroids, one must consider the size and tensile strengh of the object to determine if it will remain together.

Comets, on the other hand, would probably elongate slightly before impact.

[jlhredshift]

The result might look like what happened to Iapetus (http://saturn.jpl.nasa.gov/video/videodetails/?videoID=162) if the impactor wasn't too big.

[chornedsnorkack]

Are you asking "how can big iron bodies stay..."?

How do big boulders stay together near the surface of the Earth? How can they roll downhill without flying apart?

Tensile strength.

The roche limit directly applies to a large body of aggregate material. For solid objects, however, such as nearly all meteors and most asteroids, one must consider the size and tensile strengh of the object to determine if it will remain together.

Mountains on Earth are only a few km high. They undergo both brittle failure (rockfalls) and ductile failure. And they are in compression throughout. Cave roofs and natural arches are usually under a hundred m in span, and usually exist because an arch is in compression throughout. Stone does not have all that much direct tensile strength. And asteroids are usually rubble piles.

What about iron? Does iron of iron meteorites readily shatter on impact, or is it tough so as to yield ductilely on impact and stay in one piece?

[rommel543]

In regards to the OP, if the impact wasn't quite enough to cause fracturing in the moon would it cause it to be knocked out of it's orbit. Intead of millions of moon pieces flying towards the planet we could have one really big one.

[mugaliens]

What about iron? Does iron of iron meteorites readily shatter on impact, or is it tough so as to yield ductilely on impact and stay in one piece?

It yields ductilely all right, and it's sheared into many pieces on impact. They've found numerous pieces in Barringer Crater (Meteor Crater), although most of the nickle-iron core was vaporized on impact.

[astromark]

jjjsssf ; welcome, but... This is MY thread and its not got anything to do with your question about a sling shot. If you want to ask that question go seek out 'Of topic babbling' That might get Your answer for you...

rommel543 ; I think the energy required to 'move' the moon would be greater than my imagined impactor... Understanding a inbound moon would be a wee bit of a problem...:(

[Jeff Root]

As Mark says, the energy required to move the entire Moon by a
"significant" amount would be much greater than the energy required
to blow a few thousand supertanker-sized chunks and a lot of smaller
debris to lunar escape speed. Any impact that could move the Moon
significantly would cause an enormous amount of fracturing and
pulverization of the rock, if not vaporization.

-- Jeff, in Minneapolis

[mugaliens]

Well... What's "significant?" If it's "measurable," a simple F-1 blasting for about a second would do the trick. If it's "visible," then that would take a far greater power (amount of energy over time).