Is a close Earth-Moon system inherently unstable?

Question

What would this do to the Earth's axis? And the seasons and precession..

Over a period of say thousands to millions of years.

At what point does downward atmospheric drag become more important than upwards gained energy from tidal friction? Would the moon be in pieces already?

What would happen if the moon were to deorbit: rings or impact event, or both?

All hypothetical of course.

Yes, I mean ridiculously close, near the Roche limit.

Answer 1

1. What do you mean by a close Earth-Moon system? For the rest of the questions that you pose, I will assume that you mean something ridiculously close, like only a couple of Earth Radii.

2. the Earth's axis should continue to precess much the way it is now--some theories suggest that the moon provides a stabilizing effect on the Earth's axis, and that the moon is one main reason why the Earth is stable enough in it's axis to support life. Bringing the moon closer would strengthen that effect. The seasons shouldn't change; they are related to the Earth's travel around the sun and the axial tilt of the Earth--which should remain stable. Precession takes thousands of years, and a closer moon might--though not necessarily--speed it up. Remember that precession is a gyroscopic effect--the spinning earth is in effect a giant gyroscope. This means that it resists changes to it's rotational axis. Bringing the moon closer would just intensify the forces felt by the Earth as a gyroscope. Would this de-stabilize the axis? I doubt it, the earth is quite massive compared to the moon.

3. Everything said so far excludes this issue--the Moon would break apart long before it got REALLY close to the Earth. The moon has a relatively low density compared to the earth, and so when it approaches within the Roche Limit, about 2.5 Earth Radii from the surface of the earth, it would experience so much more pull on the near side that it would be torn apart. The Moon wouldn't ever get close enough to feel atmospheric drag. If it could, that drag would be a VERY minor factor when compared to the Roche limit effect.

4. The moon would tear apart, and possibly form a ring system. It is extremely unlikely that the entire moon would fall to the earth, rather chunks might bump up against each other and wind up in orbits that cause them to fall to earth.

This is all hypothetical, of course. You must keep in mind that after the formation of the moon, the moon was probably much closer to the earth. Over the billions of years since formation, the moon has been moving away because of tidal acceleration, and continues to do so. If it had tried to form inside the roche limit, we wouldn't have a moon, probably just a scattered ring or just a few asteroid type moons like Mars.

Because the moon congealed beyond the Roche limit, and because the impact that created the moon added a good amount of rotational energy to the earth, the only possible situation was a moon slowly wandering away from the earth. As the moon moves away, the earth is slowing its rotation.

Here are some links to get started on studying all this for yourself, though I suspect that you already have. Hope the thoughts I gave were helpful!

Answer 2

As long as there are no outside influences (gravitational, magnetic, etc.) then the system is stable. But influences from the sun and the other planets could destabilize the system over time. The moon and earth were formed about the same time (4.5 billion years ago) and have been stable all the time.

Since the moon orbits outside our atmosphere, and indeed is actually receding from the earth at the rate of about 4 cm per year, then atmospheric drag isn't an issue.

If the moon were to spiral in towards the earth, it would eventually be torn apart by earth's tides when it gets to the earth's Roche limit (depending on the actual rigidity of the moon this is between about 9500 km and 18000 km). The material of the moon would form rings around earth, and depending on the momentum of the moon's orbit towards earth the rings would either remain in orbit (like Saturn), or would eventually spiral into the atmosphere and either burn up or crash on earth.
Before that, the changing direction and strength of the moon's gravity could influence our tides (higher or lower than normal). This would affect the weather, causing droughts and floods and disturbing ocean life and the ocean currents.
As well it could cause some wobbling of the earth on it's axis (not much, but possibly enough to cause earthquakes and powerful weather systems). This could alter the precession of the equinoxes slightly, though that probably wouldn't affect us much. But the seasons might change, especially if the angle of the moon's gravity on earth were just right at the right strength to change our axial tilt - that could be a major disaster since the tilt is what gives us our seasons.

All hypothetical of course.

Answer 3

At roughly 6,000 miles above the Earth's surface, which is at Roche's Limit, if the moon were to orbit that closely, it will distingrate through gravitational tidal forces exerted by Earth. A lot of the matter will fall towards Earth, the rest will form a ring around Earth, and very likely smaller moons will form once again during this process. Having this much matter falling and combining with the Earth will definitely alter its axis tilt, and during this forcible change of it, the precession will become more pronounced, so possibily for millions or hundreds of millions of years the Earth will undergo eras of relatively mild seasonal changes to eras of more extreme seasonal changes. It would definitely be very interesting times.

However, after the moon had formed early in the Earth-moon history beyond Roche's limit, because of "tidal drag", the moon's orbital speed has been dropping and hence it has been receding from the Earth to where it is today. And the Earth's own rotational speed dropped from 10 hour days to the 24 hour days we have today. Now, "tidal friction" is more than just the actions of the oceans upon the land masses, it's also the plastic deformation of the upper mantle and crust of the Earth, as well as the moon. To understand how this creates an internal friction, imagine that we have an elliptical pot of water, and "spun" the water. The whirlpool of water will come to a rest much more quickly than if the pot was circular, because the body of water cannot spin freely without deformation.

Answer 4

Fist of all, it isn't the way interplanetary return and forth works. You launch your automobile right into a circulate orbit that's an ellipse that's tangential to the orbits of the two Earth and Mars. You time the launch so as that the automobile reaches the orbit of Mars on the comparable time and place that Mars itself does. that's an elliptical orbit this is totally between the orbits of Earth and Mars, and would not come everywhere close to the sunlight. Your 2nd question seems to be extra approximately looking a right away line with the aid of area between the Earth and Mars, which isn't useful for many motives, maximum serious of that's that that is going to require massive means. besides the indisputable fact which you will _look_ in a right away line from Earth to Mars almost each and each of the time, aside from a truly short era while Mars is on the some distance element of the sunlight. How close you may persist with Mars while it passes in the back of the sunlight relies upon on the nicely-known and site of your telescope. We right away watch planets pass in the back of the sunlight with the SOHO image voltaic observatory satellite tv for pc, while Mars is purely out of sight for some days, if in any respect.

Answer 5

Hi. The pair seems to have been stable for several billion years.