Asteroid hits moon → moon hits Earth possible?

[crossinggo]

Fascinating thread! Revisiting a small piece of the discussion, could a large enough object pass by the moon without striking it, having the effect of destabilizing the moon's orbit around Earth? So that eventually it would spiral into the Earth, even over a long period of time? Allowing that the gravitational effects might ravage Earth well before the impact ever happened.

And if that is possible despite being incredibly unlikely, would such a fly-by that could disrupt the moon's orbit also create havoc on the Earth (from our point of view) so we might not be around when the moon finally smashed us?

 

[DaveC426913]

Fascinating thread! Revisiting a small piece of the discussion, could a large enough object pass by the moon without striking it, having the effect of destabilizing the moon's orbit around Earth? So that eventually it would spiral into the Earth, even over a long period of time? Allowing that the gravitational effects might ravage Earth well before the impact ever happened.

And if that is possible despite being incredibly unlikely, would such a fly-by that could disrupt the moon's orbit also create havoc on the Earth (from our point of view) so we might not be around when the moon finally smashed us?

Sure it could.

 

[DaveC426913]

Speaking of near-misses...

Anyone hear about the 7metre asteroid that passed within 14,000km of Earth last week?

Yes, 14,000km. Twenty times closer than the Moon.

Skywatchers spotted it only days before closest approach.

 

[qraal]

Hi All

Of course the Moon could suddenly get a lot closer by losing orbit energy due to a flyby of a rogue Mercury. I read this rather disturbing paper that was just posted on the arXiv...
"[URL
An Overview of the 13:8 Mean Motion Resonance between Venus and Earth[/URL]

...which describes very rapid (~Myr) scenarios in which the eccentricity of the planet Mercury is chaotically amplified, sending it careening past the orbits of Venus and Earth. Venus's inclination needs to increase to only 7^o for Mercury to start getting pumped up in eccentricity.

Makes me wonder just where the planets were a few aeons ago. Could the "Faint Young Sun" paradox be explained by a more eccentric orbit?

 

[Lsos]

If the moon were to STOP with respect to the earth, as has been asked earlier, and then allowed to fall...would it actually hit the Earth in abut 6 days (as has been suggested), or would it build up speed (up to 9km/s was calculated), end up missing the earth, and simply go into another orbit?

 

[qraal]

If the moon were to STOP with respect to the earth, as has been asked earlier, and then allowed to fall...would it actually hit the Earth in abut 6 days (as has been suggested), or would it build up speed (up to 9km/s was calculated), end up missing the earth, and simply go into another orbit?

The mutual gravity of the Earth and Moon would draw them together. There's a minimal amount of transverse motion needed to prevent them from colliding, which can be computed as the velocity needed for the centre of mass of the Moon to pass the Earth's centre of mass at a distance equal to the sum of their radii. More or less. Real Earths and Moons would experience energy loss due to tidal deformation so the actual transverse velocity needed for a miss is a bit higher. I suspect that minimal distance would be roughly the altitude at which their orbital period was equal to or more than ~6 hours, since the Moon originally evolved away from an orbit that low in the Big Smash scenario of Moon formation.

 

[timman_24]

I think you guys have forgotten to take into account the scenario of Galactus easing the moon to a rest slowly and without destroying the body.

 

[Ophiolite]

Speaking of near-misses...

Anyone hear about the 7metre asteroid that passed within 14,000km of Earth last week?

Yes, 14,000km. Twenty times closer than the Moon.

Skywatchers spotted it only days before closest approach.

Yes. An interesting one. We get hit by something that size roughly once a decade. They self destruct as an airburst.

 

[Char. Limit]

Well, if the moon was brought to a stop, its only acceleration would be towards earth, and its only velocity would be towards earth. For something to orbit, it needs to have tangential velocity w.r.t. the earth.

 

[qraal]

Well, if the moon was brought to a stop, its only acceleration would be towards earth, and its only velocity would be towards earth. For something to orbit, it needs to have tangential velocity w.r.t. the earth.

Slamming something into the Moon to stop it would bring the whole lot down on planet Earth in pieces. For the collision to have no net momentum it'd need to be an equally massive impactor traveling at the same speed strking dead-centre. A smaller impactor striking at higher speed (but same momentum) would throw off fragments of Moon that'd still orbit because the mechanical strength of the Moon is insufficient for it to all deccelerate as one mass.

 

[Char. Limit]

Oh, I'm not in any way suggesting that the moon could be suddenly brought to a stop. I'm simply saying that if it did happen, the moon would not fall into a different orbit. If an asteroid of that size/speed hit the moon, we'd all be doomed by pieces of moon and lack of tidal forces.

 

[Matterwave]

I think you guys have forgotten to take into account the scenario of Galactus easing the moon to a rest slowly and without destroying the body.

I think Galactus would sooner devour the Earth than concoct some plan involving easing the moon to rest...

In any case, I'm sure the Fantastic Four will save us!

 

[krishnaraj]

when the asteriod hits the moon in opposite direction to Earth the orbit of the moon will change depends upon the speed of the collision and the size of the asteriod.if the size of the asteriod is bigger than moon and whether has the capability to move from the orbit there is possibility ofcollision.another fact is that moon was formed from earth

An asteroid hitting the moon opposite the Earth will add energy to the Moon's orbit. Such an asteroid would make the Moon's orbit a bit more eccentric and would make the Moon's average distance from the Earth increase. To make the Moon plummet toward the Earth, the asteroid will have to hit the Moon so that it exactly cancels the Moon's orbital velocity. Such a collision would be visible on the limb of the Moon. It would still take days for the Moon to plummet to the Earth.

You can rest easy as the asteroid would have to have momentum equal to that of the Moon's orbital momentum. Since the Moon is many orders of magnitude more massive than the largest near-Earth object, the asteroid would have to have a relative velocity many orders of magnitude larger than the Moon's orbital velocity. Such an asteroid would escape the solar system.

So what about some maurauder from outside the solar system? We would see it coming. If it were big enough we would not be able to do a thing about it. Such is the stuff of multiple science fiction stories ...

 

[rmalik]

strange, I had a dream last night where the moon had broken into pieces. It was a bit chaotic too lol

 

[EdwinDurock]

Question. Everyone seems to be asking this question in the assumption the impact to the moon and Earth orbits are relatively in sync with the moon and Earth colliding. I've considered another option. How long would it take for the Earth to destabilize if the impact knocked the moon away from the earth?

 

[qraal]

Question. Everyone seems to be asking this question in the assumption the impact to the moon and Earth orbits are relatively in sync with the moon and Earth colliding. I've considered another option. How long would it take for the Earth to destabilize if the impact knocked the moon away from the earth?

How do you define 'away'? If the Moon left orbit (ala "Space:1999") then there would be some major quakes from readjustments inside the Earth due to lack of lunar tidal stresses. Then not much. Earth would be fine. It might tip over chaotically over periods of ~millions of years, but not quickly.

However if the Moon was perturbed into a highly eccentric orbit, then it's a whole different matter. Enhanced tidal forces would be bad news planet-wide. Imagine the current tectonic "Lines of Fire" turning into vast, oozing volcanic wounds in the crust and major quakes almost all the time. Earth would be a nasty, nasty place. The Moon itself might even re-experience volcanism with major implications. If there's enough volatiles it might reform an atmosphere, albeit one composed of sulfur dioxide and whatever other volcanic volatiles the Moon's mantle might harbour.

 

[Radrook]

Well, according to the latest theory the Earth has already been struck by a planet-- sized object and the resulting ejected material became the moon.

 

[qraal]

Well, according to the latest theory the Earth has already been struck by a planet-- sized object and the resulting ejected material became the moon.

Not so much the latest, just the most elaborated. A Mars-sized planet, Theia, smashed into the proto-Earth and the resulting rock-vapour cloud and debris condensed in orbit and became the Moon eventually. The core of Theia remained with proto-Earth and merged with the proto-core, while all the refractory oxides condensed as the Moon/s. If there were extra Moons, small cousins of the current one, they eventually crashed into the main Moon.

The interesting thing is that the Moon and Earth share the same levels of certain isotopes which are hard to explain if the Theia formed elsewhere in the solar system before it crashed. The latest theory is that it co-accreted with Earth in one of the Earth-Sun Trojan points before being perturbed into a walking orbit and eventual collision.

 

[llw53172]

let me ask? if the moon is a direct pull on the Earth's oceans, or the magneticness of the Earth's core, is it not possible that it could just happen that if a major event / on Earth happens it could just come too the Earth because it is from the earth? not too mention if there are objects floating around in the universe that have a greater mass x velocity then the moon it would bee possible?what affect does the oil (bp oil spill) have on the Earth and the moon? all i have thought about for some time... anyone give me some insight? i think the moon hitting the Earth is the most logical way for an event ending senerio too happen , since nothing seems too me too be out there comming towards the earth?thank you for your minds and time...L

 

[Ophiolite]

let me ask? if the moon is a direct pull on the Earth's oceans,...is it not possible .. that if a major event / on Earth happens [the moon] could just come too the Earth because it is from the earth?

In order for the moon to contact the Earth the moon or the Earth would have to be influenced by the gravity of some other body. No event occurring on the Earth could cause this to occur.

not too mention if there are objects floating around in the universe that have a greater mass x velocity then the moon it would bee possible?

There are many such objects, but none of them that we know of are likely to approach the Earth -Moon system and disturb it. Moreover, from what we know of the universe it is extremely unlikely that any such body would appear in the solar system and cause the Earth and the moon to collide. The system has been stable for 4.5 billion years. I don't expect that stability to suddenly go away.

what affect does the oil (bp oil spill) have on the Earth and the moon?

It has zero effect on the moon. It's only significant effects on the Earth are ecological, economic and political.

i think the moon hitting the Earth is the most logical way for an event ending senerio too happen ,

This may be true. However there is no reason to anticipate an 'event ending scenario'.

 

[ladykrimson]

I know this thread is a bit old, but I was wondering if anyone could answer a couple questions about the effects such a scenario would have on Earth. I understand that it is completely speculative, but I am curious to know.

1. Would Earth experience any specific effects of an impact of an asteroid with the moon? If so, what would they be?

2. As the moon careens toward Earth, what specific type of effects would Earth experience?

3. As the moon enters the atmosphere of the Earth, what specific types of effects would Earth experience?

 

[DaveC426913]

I know this thread is a bit old, but I was wondering if anyone could answer a couple questions about the effects such a scenario would have on Earth. I understand that it is completely speculative, but I am curious to know.

No asteroid would be large enough to have such an effect on the Moon as you describe. It would have to be a small planetoid.

A planetoid of that size would be big nough to perturb the Moon's orbit around Earth and Earth's orbit around the Sun.

1. Would Earth experience any specific effects of an impact of an asteroid with the moon? If so, what would they be?

It would shower the Earth with debris, most of which would burn up in the atmo.

2. As the moon careens toward Earth, what specific type of effects would Earth experience?

If we are talking a collision powerful enough to virtually stop the Moon in its orbit, then we'd have a pulverized Moon. That's the only way the Moon could end up on a direct collision course with Earth.

No, what is by far the more plausible scenario is that the asteroid perturbs the Moon and puts it in a decaying orbit bound to eventually collide with the Earth after dozens, hundreds or millions of orbits.

3. As the moon enters the atmosphere of the Earth, what specific types of effects would Earth experience?

Just Google "Earth Impact" for some awesome pix. You can deduce the effects.
[PLAIN]http://coolflowerspics.info/pictures/flowers/images/82/earth-impact1.jpg

 

[ladykrimson]

No, what is by far the more plausible scenario is that the asteroid perturbs the Moon and puts it in a decaying orbit bound to eventually collide with the Earth after dozens, hundreds or millions of orbits.

Is that like Mars' moon? Wouldn't that take a very long time to happen? What could speed up the process, maybe increase the velocity of the orbit?

I have seen many specials about what would happen if objects strike the Earth. I was fascinated to learn that there is so much more than I originally thought. For example, if a large enough asteroid impacts the Earth, I had no idea that it could raise the global temperature or set the atmosphere on fire. From what I can gather, there are specific zones of destruction, time tables, and specific angles that alter the outcome. These are the specifics that I am still learning.

Would the gravity of the moon (on its way towards the Earth) affect Earth's oceans? Tectonic activity? Electro-magnetic field?

 

[DaveC426913]

Is that like Mars' moon? Wouldn't that take a very long time to happen? What could speed up the process, maybe increase the velocity of the orbit?

Actually, increasing the velocity of the orbit would keep the moon at a distance. To cause the impact to happen sooner, you'd decrease the velocity.

I have seen many specials about what would happen if objects strike the Earth. I was fascinated to learn that there is so much more than I originally thought. For example, if a large enough asteroid impacts the Earth, I had no idea that it could raise the global temperature or set the atmosphere on fire.

Wellllll "set the atmosphere on fire" is a loose term. "on fire" literally means to oxidize. The air is already oxygen and inert nitrogen, so thte atmosphere would not be set on fire. However yes, it would get so hot that things would burn and even vapourize.

From what I can gather, there are specific zones of destruction, time tables, and specific angles that alter the outcome. These are the specifics that I am still learning.

Would the gravity of the moon (on its way towards the Earth) affect Earth's oceans? Tectonic activity? Electro-magnetic field?

Sure, but so what? That's like asking if, just before your car is totaled in a front-end collision, would the initial effects ruin your headlights and crush your bumper.

I guess if it happened slow enough, we'd get smaller effects before the end. Definitely very high tides. Shores for hundreds of miles inland would be washed out. Volcanism and earthquakes would start tearing the crust apart. When the Moon got close enough (within Earth's Roche limit) the Moon would fragment into a ring of debris. As this spread out around the planet, effects would actually even out somewhat (though it is unlikely there would be any survivors at this point or any ground for them to stand on.)

All this happens well before the Moon begins grazing the atmosphere. That's when things start vapourizing.

 

[ladykrimson]

Well, my class was discussing impact objects and their effects on Earth. We kept moving up to bigger and bigger objects, and by the time class ended, my mind was spinning different scenarios. That's why I was curious.

Do you think the surface would be molten before the Moon would even get there? Would it be due to the volcanism and earthquakes? Wouldn't that raise the temperature on the planet as well?

 

[DaveC426913]

Do you think the surface would be molten before the Moon would even get there?

Very much dependent on the scenario.

If it happened rapidly, it would probably impact before much could get molten.
If it happened slowly, Earth's crust would get rent asunder, releasing magma.
If it happened very slowly, Earth's surface might get nicely liquified like a chicken on a rotisserie.

Would it be due to the volcanism and earthquakes?

Yes, but even larger effects too. The actual distortion of the bodies into elongated ellipses would generate a huge amount of heat.

This is before the Moon separates into large chunks. I'm not sure if the Earth would get torn apart. I'm not sure if the Moon is big enough to do that.


You can read up om Roche Limits:
http://en.wikipedia.org/wiki/Roche_limit
There are examples that relate to Earth/Moon.

Wouldn't that raise the temperature on the planet as well?

That is an understatement.

 

[Radrook]

In a perceived Godless universe where rogue black holes, roge stars and even rogue planets are considered a reality, I don't see why such a scenario couldn't occur.

 

[DaveC426913]

In a perceived Godless universe where rogue black holes, roge stars and even rogue planets are considered a reality, I don't see why such a scenario couldn't occur.

Okaaay... This is kind of stating the obvious.

Pretty sure no one was suggesting it could not happen.


However, do note that this scenario is not anywhere in a vast, vast universe; it is specifically Earth/Moon.

So, no rogue planets, no rogue stars and no rogue black holes.

 

[akanura]

I just registered to reply on this even though i have nothing with physics. I googled 'moon hit earth' and found this post.

I had the same dream! It freaked me out as well. I only dreamed i was sitting at home, and when i looked outside i saw the moon, but it was HUGE and seemed to be really close. I got really scared and it freaked me out. Then suddenly i became a spectator in my dream, as floating in space. And then i saw the moon, hit the earth. I was so so scared, the Earth got damaged for a huge part, but the bigger part was still in tact.
Well HOW ODD IS THIS? 2 people dreaming about the moon hitting the earth?

 

[qraal]

akanura, we've explained at length in this thread that the Moon hitting the Earth is absurd. There's no reasonable way for the Moon to lose its orbital momentum and energy, except via exceptionally unlikely encounters with a heavy third body. Ain't happening tomorrow.