Fate Of The Moon

[rocketpost1]

Just wondering what would happen to the moon if the earth suddenly ceased to exist?. Would it migrate towards the planet with the greatest gravitational pull ?.

[jim360]

Oh wow, what a question. Erm...

I think it might depend just a little on when the Earth disappeared, because that would determine the direction in which the Moon was heading at the time. Not necessarily by much, but it might have some impact. Beyond that it would be speculation, although I suppose you could model it reasonably well with some care.

I think the Moon might stay roughly in the same place with respect to the Sun -- but I don't know this, and it might depend on a number of conditions, including those above and also why exactly the Earth "disappeared".

[jomifl]

I agree with jim, it's would keep orbitting the sun at roughly the same distance but depending on it's direction of travel when the Earth disappeared it's orbit would become more or less elliptical than at present. A huge amount of energy would be needed to move it's orbit closer to or further from the sun and there is nowhere that could come from in a 'disappearing earth' scenario.

[mibn2cweus]

I tend to agree with Jim's assessment. The Moon's orbital speed (roughly 1 km/s around the Earth) is insufficient to vastly alter it's average orbital distance from the Sun therefore in the absence of Earth's gravity, the Moon would probably settle into an orbit similar to that of the current Earth/Moon system whose orbital speed is roughly 30 km/s.

[gen2]

I don't know enough to calculate the specifics but there is a mathematical relationship between the:
Orbital velocity of the planet system
Masses of Sun and planet system
Distance between those two masses

Therefore changing the mass of the planet system (such as by removal of the earth as proposed) to leave just the lighter moon is going to change one or both of the other parameters. On the basis of the conservation of momentum, I would deduce that it would be the orbiting distance that would alter.

But which way? Will it go closer to the sun? or further away? Someone with a better grasp of physics/mathematics should be able to tell you but whichever it is, it won't gently slip into a roughly circular orbit at a new distance, rather it will enter a far more elliptical orbit passing through the point on earth's orbit where it disappeared.

[jomifl]

Gen2, The moon will stay at the same average distance as no energy will be added to or subtracted from the system.

[mibn2cweus]

The combined mutual gravitational attraction between the Earth/Moon system and the Sun is predominantly (by far) determined by the much more (by far) massive Sun, to the point that removing the Earth from the equation would have a very minimal impact on the newly established orbit of the Moon.

As was noted previously, the Moon's new orbit would be determined largely by the vector of its orbital motion at the time the Earth's influence upon the system was removed, causing a relatively small albeit significant change in its orbital period and shape. Since the Moon's orbital speed around the Earth contributes to it's overall orbital speed around the Sun the resulting orbital speed of the Moon in the absence of the Earth's gravitational influence would cause it to settle into a corresponding new orbit around the Sun.

If at the time of Earth's disappearance the Moon was moving toward or away from the Sun this would alter the eccentricity of the Moon's orbit. To the extent that the Moon was moving tangentially to The Sun at the moment the Earth's influence was removed, this would alter the Moon's average orbital speed by as much as about 3% thereby altering its mean orbital distance by as much as about +/- 9% from where it was previously.

The space station on the other hand has a much greater orbital speed around the Earth and would therefore acquire a much more significantly altered orbit in the absence of Earth's gravitational influence.

[Spoonboy]

Would you not be more worried that the Moon's moving away, if only slightly each year, would have a more dramatic impact on our planet's tides in the distant future?!!

[jim360]

No, not really, I'd be dead by then.

[sandyRoe]

And no thought for posterity?

[Spoonboy]

We will all be dead, but wouldn't you like to come back and see what it does.

[jim360]

Pfft. Not likely that anyone will be able to do anything about it directly. My understanding is that the process is slow enough such that you'd expect humans to either become extinct some other way first, or perhaps our technology will be such that it wouldn't matter anyway. Either way, it's not worry worrying about.

[jomifl]

Sandy, my thought for posterity is;
'a bit over rated the moon, sodall use on cloudy nights and spring tides were damned inconvenient'

[society]

Will the sun cool down a bit?

[jomifl]

not noticeably