Asteroid hits moon → moon hits Earth possible?

[Blue_Jaunte]

I had a vivid nightmare the other night where I went outside in broad daylight and saw that the moon was not only visible but also enormous. I saw people running around in a state of panic and asked one of them what was going on. He told me a large asteroid had struck the moon on the side opposite the one we see and now the moon was going to crash into Earth. I could hear a distant radio well enough to make out an announcer say "...it's a matter of hours now, not days". Understandably, I was a bit shaken when I woke up.

So is such a scenario even possible? Could an asteroid collision with the moon send it out of orbit and careening into us? Would such a collision be a global-killer?

Thanks

 

[D H]

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 ...

 

[Chris Hillman]

Of course, if an asteroid or meteor strikes the Moon, it might well happen that a small piece of the Moon might be ejected and eventually happen to strike the Earth. Similarly for Mars (indeed, certain rare meteorites are thought to have originated in just this fashion.)

But if you want to have more realistic nightmares, dream about something like the next global pandemic. Or dying of thirst. Or the economy crashing. Or a combination. That chances of a major asteroid strike occurring in your lifetime are extremely remote.

 

[Astronuc]

Geez - I saw "Asteroid hits moon " and thought - wow what an event. Then when the thread opened, I saw that it was a hypothetical.

It would still take days for the Moon to plummet to the Earth.

That would make an interesting calculation. Take the moon and Earth released from rest at their nominal distance and determine how long it would take for them to come together. Acceleration is not constant.


The consequences of an asteroid/Moon collision of course depend on the size of the asteroid. It would certainly make a crater, which is how the craters got made way back when. The would be some ejecta coming out of the impact area.

 

[tony873004]

That would make an interesting calculation. Take the moon and Earth released from rest at their nominal distance and determine how long it would take for them to come together. Acceleration is not constant.

5 days 6 hours 6 minutes from apogee
4 days 19 hours 19 minutes from the Moon's average distance
4 days 7 hours 44 minutes from perigee

This assumes an initial velocity of 0. Of course, the asteroid could knock the Moon towards or away as well yielding an initial radial velocity other than 0.

 

[D H]

That would make an interesting calculation. Take the moon and Earth released from rest at their nominal distance and determine how long it would take for them to come together. Acceleration is not constant.

I wrote a simple velocity verlet integrator in Excel. Nothing much of interest happens for the first day. After one day, the Earth-Moon separation drops by a mere 2.6% and the relative velocity reaches 0.24 km/sec. It takes 3.3 days for the velocity to climb to 1 km/sec, at which time the Earth-Moon separation has dropped by nearly a third. Things get interesting on the final day. After 4.8 days or so, the Earth and Moon finally collide with an impact velocity of about 9 kilometers per second.

 

[cpalms]

The force it would take an asteroid to do something like that is mind boggling.Bordering on impossible.Plus the affect the moon coming closer to the Earth would have would be devastating without it crashing into it.The immense gravity change would probably cause flooding throughout the planet.You would think right?

 

[Michael Mozina]

No known or identified asteroid could do that. As DH pointed out, any asteroid traveling at that kind of speed would be moving too fast to be trapped by the gravitational influence of our sun. It would have to come from outside of the solar system, and it would have to be traveling at many orders of magnitude faster than anything inside our solar system.

 

[Michael Mozina]

I wrote a simple velocity verlet integrator in Excel. Nothing much of interest happens for the first day. After one day, the Earth-Moon separation drops by a mere 2.6% and the relative velocity reaches 0.24 km/sec. It takes 3.3 days for the velocity to climb to 1 km/sec, at which time the Earth-Moon separation has dropped by nearly a third. Things get interesting on the final day. After 4.8 days or so, the Earth and Moon finally collide with an impact velocity of about 9 kilometers per second.

Just out of curiosity, how did you calculate the time it would take to impact?

 

[D H]

Just out of curiosity, how did you calculate the time it would take to impact?

I used numerical integration techniques, specifically a velocity Verlet integrator.

Herein I place an upper bound on the time. For simplicity, assume the initial lunar orbit is circular with an orbital radius of a and period T. Now suppose the Earth and Moon are point masses rather than solid masses. I don't have to worry about the actual collision with this assumption. If all but a tiny fraction of the Moon's initial tangential velocity is canceled at some point in its original circular orbit, the point mass Moon and Earth will now orbit each other in a highly elliptical orbit with some semi-major axis a_e. By Kepler's third law, the period of this new orbit will be T_e = T\;(a_e/a)^{3/2}. The time from apogee to perigee is half the orbital period. If a collision between the real Earth and real Moon occurs, it will be sometime before this half period interval: T_c < T_e/2 = 1/2\;(a_e/a)^{3/2}\;T.

In the limit that the tangential velocity becomes zero, the semi-major axis of this new orbit is simply half the semi-major axis of the original orbit. Thus

T_c < \left(\frac1 2\right)^{5/2} T

Since the moon's orbital period is 27.32 days, the collision will occur in less than 4.83 days. Note that this agrees with the result obtained by numerical integration. The upper bound is very close to the collision time as the Moon's velocity is awfully high at the time of collision and would grow even higher if only the Moon and Earth were point masses.

 

[BrainTeaser48]

Consider changing the direction of a rolling bowling ball. In order to change its direction significantly you would need to match its momentum with an object of similar momentum. A BB would need to travel well above the speed of a bullet to have an effect, but another bowling ball needs only be in its way. The Moon would need a massive body to change its orbit significantly enough to approach the Earth. Such an event would destroy the moon. Any planetary body has the consistancy of a creampuff with respect to such colisions. Also, the trajectory is the only change that would occur unless the moon is slowed down in its orbit since the angular momentum would continue to carry most debris of such an event in its original orbit.

 

[Michael Mozina]

I used numerical integration techniques, specifically a velocity Verlet integrator.

Thanks for that explanation. I appreciate it.

 

[cesiumfrog]

Another way to approach this nightmare: Such an asteroid would have to not only have great momentum, but would need to strike at a very specific angle.

But if the same asteroid hit the earth, it would wipe us out no matter what the angle was. And the Earth is a much bigger target. And even a comparatively much smaller (and slower) asteroid would still be enough to do this.

So rest assured that it is far more likely that civilisation will end due to a direct impact (with little warning at all since, realistically, it just isn't easy to spot an asteroids at long distances) rather than by some improbable trick-shot that gives you the luxury of watching the moon grow for some number of minutes.

 

[andrewj]

collision

Of course, if an asteroid or meteor strikes the Moon, it might well happen that a small piece of the Moon might be ejected and eventually happen to strike the Earth. Similarly for Mars (indeed, certain rare meteorites are thought to have originated in just this fashion.)

But if you want to have more realistic nightmares, dream about something like the next global pandemic. Or dying of thirst. Or the economy crashing. Or a combination. That chances of a major asteroid strike occurring in your lifetime are extremely remote.

yes dying of thirst is bad news but it was just a thought a possible aesteroid moon collision

 

[Count Iblis]

The Moon could also make a spontaneous quantum jump to a lower orbit.

 

[DaveC426913]

Man, what would the energy of that released photon be?

 

[pervect]

I'm a bit dubious about the possibility of such a thing happening. It corresponds to a forbidden quantum transition. It definitely couldn't happen with a single photon if you want to conserve energy and angular momentum, but some sort of multi-photon process might make it possible - I'm not really positive it's possible even so, but I'm not positive it's impossible, either.

 

[Count Iblis]

Many gravitons, not photons, must be emitted. Classically, a system of two rotating bodies will emit continuous gravitational radiation. If you look at it more precisely (i.e. quantum mechanically), you see that the system makes jumps to lower energy states emitting gravitons. Selection rules apply to matrix elements <a|H|b> where H is the effective Hamiltonian of the gravitatonal field in second quantization. But to higher order in peturbation theory the amplitude for the transition probability contains terms

<a|H|b1><b1|H|b2>...<bk|H|b>

corresponding to emission of many gravitons...

 

[JustVisiting]

Please humor my curiosity.
Has anyone examined the concept of diverting a near-Earth asteroid towards the Moon? Would such an effort alter the orbital path of the Moon? It would seem to be easier to do, since the gravitational pull from the Moon would assist at some point.

 

[russ_watters]

Welcome to PF.

Has anyone examined the concept of diverting a near-Earth asteroid towards the Moon?

Except as you just did, with a speculative hypothetical, no.

Would such an effort alter the orbital path of the Moon?

Certainly. But how much? Answer: not enough to matter. Consider that all those craters we see on the moon were caused by near-earth asteroids hitting it. And since the far side isn't shielded by earth, it looks even worse!

 

[Researcher X]

I wonder how fast Ceres would have to go to do it (being the largest asteroid/planetoid available), not that it would ever do so (mad scientist?)...

I looked this up, and amusingly, the momentum of ceres even at a blistering nonsensical speed of Mach 1000 (about the speed of solar wind) is less than the moon's orbital angular momentum by a factor of 10 billion, despite having 3.4 times the kinetic energy needed to scatter the moon permanently (approx 4.053e29 joules).

So, really, even if the conditions were right, it looks like the moon would be destroyed by an impact long before it was harsh enough to perturb its orbit significantly. Doesn't make sense to me.

 

[Chronos]

That would be a whopper of an asteroid, much larger than any known asteroid in our solar system. A smaller asteroid would need to travel very fast to knock the moon out of orbit. So fast that it would blast chunks out of the moon, which would pretty much spoil the whole effect.

 

[Vanadium 50]

I looked this up, and amusingly, the momentum of ceres even at a blistering nonsensical speed of Mach 1000 (about the speed of solar wind) is less than the moon's orbital angular momentum by a factor of 10 billion, despite having 3.4 times the kinetic energy needed to scatter the moon permanently (approx 4.053e29 joules).

You can't compare linear and angular momentum. They have different units.

Ceres weighs about 1.2% of what the moon does. It will be difficult to make a comparison where there is a factor 10 billion difference between them.

 

[D H]

In fact, Ceres hitting the Moon head-on at 80 km/s (Mach 230) (Earth-relative velocity) will do the trick. What would give Ceres a velocity of 80 km/s is of course a different trick.

 

[Count Iblis]

In fact, Ceres hitting the Moon head-on at 80 km/s (Mach 230) (Earth-relative velocity) will do the trick. What would give Ceres a velocity of 80 km/s is of course a different trick.

There can be a Ceres sized asteroid kicked out from another solar system that would enter our solar system. It could have the required velocity, because an object arriving from rest at infinity can already have a maximum relative velocity w.r.t. Earth of 72 km/s.

 

[D H]

There can be a Ceres sized asteroid kicked out from another solar system that would enter our solar system. It could have the required velocity, because an object arriving from rest at infinity can already have a maximum relative velocity w.r.t. Earth of 72 km/s.

With respect to what body? Earth escape velocity at the Moon's mean orbital distance is 1.4 km/s. Solar system escape velocity at 1AU is 42.1 km/s. Add them together and you get 43.5 km/s, not 72.

 

[Count Iblis]

With respect to what body? Earth escape velocity at the Moon's mean orbital distance is 1.4 km/s. Solar system escape velocity at 1AU is 42.1 km/s. Add them together and you get 43.5 km/s, not 72.

42 km/s plus 30 km/s of Earth in its orbit around the Sun.

 

[Count Iblis]

To see what would happen if Ceres were to collide with Earth with such speeds, see here:

http://www.lpl.arizona.edu/impacteffects/

 

[Sir Pwn4lot]

It's a superficial question since the chance of an asteroid of sufficient mass to have such an effect colliding with the Earth within the next few generations is almost negligible, the chance of one hitting the moon is astronomically minute.

Besides, for those who watch Stargate, you could make the moon simply go faster than the speed of light and go THROUGH the earth, I loved that ep lol.

I'd be more concerned about religious fanatics like Bush or Palin getting control of the launch codes and blowing us all to hell...

 

[ray b]

That would be a whopper of an asteroid, much larger than any known asteroid in our solar system. A smaller asteroid would need to travel very fast to knock the moon out of orbit. So fast that it would blast chunks out of the moon, which would pretty much spoil the whole effect.

would not any impact of that force level shatter both our moon and any object that hit it
in to dust and fairly small chunks

 

[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'.