Comet or Asteroid smashes into OUR moon!

[EastNamibianSpaceMiningCo]

Here is the scenario:

 

Quote

A comet or asteroid smashes into our moon suddenly and unannounced.

 

Our moon is either destroyed, broken into several pieces or knocked off of its orbit.

 

(For the purposes of this scenario, no lunar "bits" or debris fall into Earth. We are concerned with effects on tide and tectonics etc.)

 

How deeply in trouble are we?

 

Will this impact event (on our MOON) affect Earth's tides? Will global havoc be wreaked by tidal waves, earthquakes and tsunamis? What great effects will this have on our gravitational equilibrium in the solar system? Will this be Armageddon?

Edited October 26, 2019 by EastNamibianSpaceMiningCo

[mathematic]

For this to happen (moon breakup) you need a very large object - much bigger than known asteroids.  If it does happen, the result depends on size of the big rock, how fast it was moving, impact direction, etc.

[Janus]

The Moon already produces tides in both the Oceans and the Earth itself.   If something with a significant amount of energy where to hit the Moon, there are a few possibilities:

1. Moon shatters, but the resultant pieces do not have enough energy to overcome the gravitational binding energy of the Moon.  The pieces separate and the then fall back together to reform a moon-massed object.  The Moon's orbit will likely be changed.

2. Moon shatters with enough energy to it from reforming but not enough for them to escape the Earth's gravity.  The pieces end up forming a ring around the Earth.

3. Moon shatters with enough excess energy to knock the pieces completely free of the Earth entirely.

 

The tidal effects caused by case 1 depends on the new orbit.  If the collision alters the orbit so that on average it is closer to the Earth, we would get larger lunar tides, the closer to the Earth it gets, the stronger the tides.  For them to be Armageddon scale would require it to get really close.

Case two would have the tides caused by the Moon weakening as the ring formed. We'd still have solar tides.  This could take a fare bit of time, so I don't see this as being a sudden change. The Earth is already used to being flexed on a 12 hr or so cycle, so I don't see it reacting violently to having this flexing weakening over time.

With case three, the Lunar tides would weaken as the debris field gets further from the Earth. Again this will not be fast, and not cause much stress on the Earth.

So really, only case 1, where the collision robs the Moon of enough orbital energy to give it a close perigee would produce greater tidal forces.   I think it would be difficult for such an impact to have enough energy to  lower the perigee significantly without imparting enough energy to shatter the Moon into a ring.

[Airbrush]

An object large enough to "destroy" the moon is also large enough to pull the Earth off its' orbit.

[J.C.MacSwell]

53 minutes ago, Airbrush said:

An object large enough to "destroy" the moon is also large enough to pull the Earth off its' orbit.

It depends on what you mean by "it's orbit". It would have to be awfully big to send it into the Sun or slingshot it into escape velocity mode.

 

[swansont]

3 hours ago, Airbrush said:

An object large enough to "destroy" the moon is also large enough to pull the Earth off its' orbit.

It’s not obvious to me that this is true. The ability to damage the moon would depend on momentum and energy, which can be large if v is large. Affecting the earth’s orbit would (largely) be a function of mass, and interaction time. A relatively small mass moving fast would minimize both.

[Airbrush]

2 hours ago, J.C.MacSwell said:

It depends on what you mean by "it's orbit". It would have to be awfully big to send it into the Sun or slingshot it into escape velocity mode.

 

How big an object does it take to destroy the moon?  How much could Earth's orbit be perturbed by such an object passing nearby?

Edit:  I just saw your post above.  A very fast moving object could "destroy" the moon and be gone before Earth's orbit is much disturbed.  But what is the likely range of speeds of your average object that can destroy the moon?  Up to about 10 miles per second would need to be about half the size of the moon.  Could such an object be around long enough to cause catastrophic disruption of Earth's orbit?

Edited October 28, 2019 by Airbrush

[swansont]

10 minutes ago, Airbrush said:

How big an object does it take to destroy the moon?  How much could Earth's orbit be perturbed by such an object passing nearby?

That’s something one might expect you to know if you’ve claimed “An object large enough to "destroy" the moon is also large enough to pull the Earth off its' orbit.”

 

[Janus]

14 minutes ago, Airbrush said:

How big an object does it take to destroy the moon?  How much could Earth's orbit be perturbed by such an object passing nearby?

Edit:  I just saw your post above.  A very fast moving object could "destroy" the moon and be gone before Earth's orbit is much disturbed.  But what is the likely range of speeds of your average object that can destroy the moon?  Up to about 10 miles per second would need to be about half the size of the moon.  Could such an object be around long enough to cause catastrophic disruption of Earth's orbit?

An object less than 1 tenth the mass of the Moon with a relative velocity of 50 km/sec would have about  ~ 9e30 joules of KE, which is some 76 times the gravitational binding energy for the Moon.  An extra-solar object would be moving at least 42 km/sec relative to the Sun at Earth orbit distance.  At the right approach angle, a 50 km/sec relative velocity with respect to the Earth-Moon system is not unreasonable. 

The Gravitational sphere of influence( the distance at which its gravitational effect is significant compared to the Sun's) for a object 1/10 the mass of the Moon is  actually quite a bit less than the Earth-Moon distance, so I don't see its hitting the Moon as having much of an effect on the Earth's orbit.

[Airbrush]

8 minutes ago, Janus said:

The Gravitational sphere of influence( the distance at which its gravitational effect is significant compared to the Sun's) for a object 1/10 the mass of the Moon is  actually quite a bit less than the Earth-Moon distance, so I don't see its hitting the Moon as having much of an effect on the Earth's orbit.

That's good to know.