Kkelloww said:
The effects on Earth if the moon was in a highly eccentric orbit. perigee about 35,000 km which is outside the Roche limit I believe. Could such an orbit be sustainable. Also, what would the orbital period be and how far would apogee distance be?
How fast would it orbit Earth during perigee distance?
These things are pretty interdependent on each other. Just having the perigee isn't enough, as a perigee of 35,000 km can describe an infinite number of orbits. If you had the perigee and one of the other properties of the orbit, (period, apogee, orbital speed at apogee) you can work out the rest. So for example , if the apogee happens to be equal to the Moon's present distance, then you can work out that the orbital period would be ~11 days and the orbital speed at perigee would be ~4.6 km/sec
Tidal effects vary by the inverse of the cube of distance. Since 35,000 km is almost 1/11 the present distance of the Moon, tidal effects would be over 1300 times greater.
The major effect the Moon has on the Earth's axial tilt is precession, Which alters the direction of the tilt, but not its angle. when the Moon is at perigee this will be magnified. But he over all effect will depend on the overall orbit. The present effect causes the Earth to go through one full precession cycle every ~25,000 yrs. If the average distance of the new orbit is smaller, this will speed up. If it is larger, then it could well slow down. [/quote]
Increased volcanism
[/quote] Maybe. The increased flexing of the Earth's crust could lead to more crustal heating. It would be really hard to estimate to what degree this will effect volcanism.
Affect on wind speed and patterns
Probable. The Moon already produces an atmospheric tide, but it is much weaker than the effect caused by solar heating. Amping it up by a factor of 1,300 would likely turn it into a major factor, producing low pressure regions at the antipodes during perigee.
Erratic seasonal weather.
Weather is a very complex system, so it is very hard to predict exactly what kind of overall climatic changes can be produced by something like severe lunar atmospheric tides, but it is likely to upset the climate.
Any possible effects on Earth's magnetic field?
probably not
Could tidal forces on the Earth and moon cause this orbit to decay?
No. Not unless the orbit is such that the orbital period is less than the rotational period of the Earth. If this is not the case, then tidal effects will tend to raise ( and circularize the orbit.) But this effect will still be fairly slow.
Finally,
Is there any possible way in which the moon could orbit the Earth at the perigee distance for an extended period of time?
Not without a secondary effect from something. For instance, it would take something acting on the Moon to throw it into a new orbit with a 35,000 km perigee. It would take something else acting on the Moon in just the right way while it was at perigee to cause it to settle into an orbit at perigee distance. Otherwise it swings into perigee and then swing out to apogee. Depending on the eccentricity of the orbit, it could spend the vast majority of its time much further away, since it will be moving much faster near perigee than when near apogee and spends more of its time at a further than average distance than it does at a closer than average distance. (think about Comets that speed decades in the outer reaches of the solar system, and then come swooping in, spending just a few months in the inner system.)
Crazy stuff I know. Thanks in advance!
Hope this was of some help.
