Asteroid hits moon → moon hits Earth possible?

[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.

 

[akanura]

I know but its weird, that 2 people have the same dream, and its not the most common dream. Its not as if we dream about flying or w/e Just scares me that someone dream the same odd **** that doesn't have a dream symbol, as me!

 

[Ryan_m_b]

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?

I know but its weird, that 2 people have the same dream, and its not the most common dream. Its not as if we dream about flying or w/e Just scares me that someone dream the same odd **** that doesn't have a dream symbol, as me!

It isn't odd at all, after all every year there are over two and a half trillion dreams! And an asteroid hitting the moon isn't even that weird a concept. Now let's stick with what the thread is actually about and not get dragged into any crazy speculation on dreams.

 

[NeedtoKnow]

It isn't odd at all, after all every year there are over two and a half trillion dreams! And an asteroid hitting the moon isn't even that weird a concept. Now let's stick with what the thread is actually about and not get dragged into any crazy speculation on dreams.

Here is my one comment about this dream and the moon knocked out of orbit by asteroid/planetoid concept...Could it be that somehow you and that other dreamer either read or heard about these works of young adult fiction by Susan Beth Pfeffer?
Life As We Knew It (pub. 2006), The Dead And The Gone (pub. 2008), and This World We Live In (pub. 2010) aka the Last Survivors series .

 

[Ryan_m_b]

Here is my one comment about this dream and the moon knocked out of orbit by asteroid/planetoid concept...Could it be that somehow you and that other dreamer either read or heard about these works of young adult fiction by Susan Beth Pfeffer?
Life As We Knew It (pub. 2006), The Dead And The Gone (pub. 2008), and This World We Live In (pub. 2010) aka the Last Survivors series .

I didn't have a dream. I was responding to someone who claimed to have a dream about it. Whilst I've never heard of Pfeffer I don't doubt that some of her readers may have had a dream like that. The majority of people though are just dreaming of a fairly simple idea.

 

[ninevoltz]

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?

That makes four of us now, I had the same dream too, several months ago. I was starting to wonder now that 2005 YU55 will be passing by, could it really happen? Good to see smarter people than myself able to explain why it could NOT happen.

 

[Xanya]

I had this dream last night. I googled "could the moon hit Earth" and found this page. I consider myself a person of science and would not normally believe in this scenario, however, it disturbs me that my subconscious mind would create this event even though I think it ridiculous. Then to find out that other people have had this dream is really bothersome. I know I have never seen any movie or media that would influence my dreams to create such an event. Is there any way that this COULD possibly happen?

 

[qraal]

I had this dream last night. I googled "could the moon hit Earth" and found this page. I consider myself a person of science and would not normally believe in this scenario, however, it disturbs me that my subconscious mind would create this event even though I think it ridiculous. Then to find out that other people have had this dream is really bothersome. I know I have never seen any movie or media that would influence my dreams to create such an event. Is there any way that this COULD possibly happen?

Presuming you're not a troll and multi-posting just to annoy people, then - as this thread explains - the described event basically has a ZERO probability. There's no way something can hit the moon and cause it to fall into the Earth. Even if the Moon was totally shattered, that wouldn't cause it to fall to Earth.

 

[Xanya]

Presuming you're not a troll and multi-posting just to annoy people, then - as this thread explains - the described event basically has a ZERO probability. There's no way something can hit the moon and cause it to fall into the Earth. Even if the Moon was totally shattered, that wouldn't cause it to fall to Earth.

Thank you for your response. No, I'm not a troll and normally wouldn't take the time to post on forums, but as this dream was very vivid, disturbing, and since other people have had the same dream, I thought it would be worth sharing. I actually wrote it down and noted in on my FB page as follows:

My Nightmare

May-2-2011

I was standing outside; I don't remember where I was or who I was with, I only know that I was not alone. It seemed as though it should have been nighttime though it was very bright out. I remember that my gaze was transfixed on the sky and I felt an incredibly vivid sense of disbelief and the most horrifying feeling of sadness and anguish which Shakespeare himself couldn't possibly begin to describe.
I can recall -very clearly- looking into the sky at the moon, but it was approximately 50 times larger than normal. Basically, the massive silvery-yellow body had captured the entire area of my peripheral view. I could visibly make out detailed surface formations of the object which would normally have been unnoticeable to the naked eye as it appeared to slowly draw closer to the Earth.
My memory of the dream gets somewhat hazy at this point, but I do recall checking some form of news media to get updated information on the event. I specifically remember feeling concerned about the time until impact.
The realness of the dream was so intense that I'm still consumed by the indescribable emotions which pulsate through my soul upon its recollection. The fact that my subconscious mind would devise such an event, considering that to the best of my knowledge the laws of physics and thermodynamics render it impossible, has me most perplexed. What's even more troubling, is that upon my Googling the possibility of a "moon hitting Earth" scenario, I've discovered that many other people have had nearly the exact same dream...and that's just creepy!


Please note that nothing in my dream gave any indication that the moon was actually struck by another object. Then again, considering the size it was in my dream, I would assume I missed the cause of its new trajectory.

 

[Ryan_m_b]

I don't see any need to keep this thread open; over 7 billion dreams happen every day. The fact that some of them are similar and involve an object in the sky and an object under their feet is nothing special.