A question about planetary orbit

[xelasnave]

I understand the Moon moves further out over time such that its orbit increases in diameter over time.

Firstly is this correct.

Second.. Do the other planets increase or decrease their orbits over time?

Third.. Do the Moons of other planets move further out over time?

These are question I ask because I don't know the answers by the way.

alex

[multiweb (Marc)]

Saw this documentary on Foxtel a while ago that explained the moon was formed from the earth during a massive collision with a smaller planet intersecting earth's orbit very early during the solar system formation. As a result today's earth is now bit smaller and the moon was very close orbiting earth at the beginning then progressively got further.

[renormalised (Carl)]

Yes, to all of them

The orbits of all planetary bodies change shape all the time, over long periods of time. The Moon is moving further away by about 2-3cm a year, due to tidal forces between it and the Earth transferring our rotational angular momentum into its orbital motion. Eventually, our day and its day will be the same length...about 30-36 days long. Not only that, but the planet's orbits are changing their shape all the time, due to the various gravitational forces being exerted upon them. Changes in ellipticity, orbital tilt, points of perihelion and aphelion etc, all occur to the planets over time. Some orbits become more elliptical, others round out. The moons of the other planets all follow the general trend of changing orbits over time...some move in or out, others become more highly inclined and others less so. All due to the gravitational forces being exerted upon them and how these forces between the bodies balances out.

[renormalised (Carl)]

Originally Posted by multiweb

Saw this documentary on Foxtel a while ago that explained the moon was formed from the earth during a massive collision with a smaller planet intersecting earth's orbit very early during the solar system formation. As a result today's earth is now bit smaller and the moon was very close orbiting earth at the beginning then progressively got further.

Actually Marc, the Earth gained mass. The impactor was about the size of Mars (except a little heavier). It was a glancing collision but the impacting planet was completely destroyed. Most was absorbed by the Earth, but some of the rock...mostly from the impactor's mantle regions (although there are questions about this) ended up in orbit and eventually condensed into the Moon. The Moon was very close to the Earth...originally not much more than 19000 miles, but in an elliptical orbit. Eventually the orbit rounded out, but not before the Moon reached it's closest point to the Earth in its orbit, about 2.1 billion years ago...at about 18000 miles. Since then, it's gradually moved on away till it's where it is now. Eventually, it'll end up about 750K-1 million miles out in a 36 day or so orbit. Our own day, by then, will also be that long due to loss of rotational momentum being transferred out to the Moon.

[xelasnave]

Thank you Carl.

I think many folk including myself would think the opposite is true such that finally everything spirals in to our Sun approach.

How extremely interesting

I have been wondering for some time now why we can have an expanding space (easy to answer in a push universe) but trying to fit it into what is acceptable and what is not and I have read a little about dark energy etc ...but whilst wondering about that I wondered if matter also is expanding (currently I think the popular view is space expands and matter does not..like the raisins in the cake trip..but what if the raisins got bigger..in some proportion to the expanding space which I imagine would be density driven...and how that may effect time as well.

AND that question may or would turn on where space ends...so where does space end?

Does it end somewhere above our atmosphere? or can we consider space to occupy all regions... even the region between an electron and its nucleus, even the regions between the virtual particles that spring back and forth from their parent particle?

When I am trying to comp template nothing I always find there is always something so I find it hard to imagine any empty space really.

I read someplace , which I gave no heed or credit to at the time nor do I now but mention it nevertheless, that the Earth is actually growing is mass ..or size (volume) I cant remember which but if there is anything behind that claim maybe matter expands in some proportion to the expansion of space...mmmm there is so much to learn about let alone understand.

Oh well back to utube...been looking at everything on the standard model and higgs bosen etc but at the moment it is S Hawking Master of the Universe and decided to add him to my list of heros
alex

[bartman (Bart)]

Originally Posted by renormalised

.originally not much more than 19000 miles, .

Just wondering why your using miles when earlier you used metric?

"further away by about 2-3cm a year,"


Bartman

[renormalised (Carl)]

Originally Posted by bartman

Just wondering why your using miles when earlier you used metric?

"further away by about 2-3cm a year,"


Bartman

Does it really matter??!!

Force of habit...anyway, 19000 miles sounds a lot closer than 31600km

[CraigS]

Actually, there's lots of interesting anomalies about the moon.

Eg: 1) Mascons:

"The gravitational field of the Moon has been measured through tracking the Doppler shift of radio signals emitted by orbiting spacecraft. The main lunar gravity features are mascons, large positive gravitational anomalies associated with some of the giant impact basins, partly caused by the dense mare basaltic lava flows that fill these basins. These anomalies greatly influence the orbit of spacecraft about the Moon. There are some puzzles: lava flows by themselves cannot explain all of the gravitational signature, and some mascons exist that are not linked to mare volcanism."

I've read, (but this may be an urban myth), that this is why so many early survey satellites crashed .. ie: because, at the time, no-one knew when to counteract the effect of gravitational variations in the satellites' orbits as they flew over.

2) Density
Perhaps also a myth: {NASA left behind seismometers with the moon landings. They intentionally de-orbited a satellite which had reached the end of its 'use by date' and crashed it so they could get the results from the seismometer. Apparently, the moon 'rang like a bell' for a good hour or so}.

This may not actually be a myth because "The Moon is the second densest satellite in the Solar System after Io. However, the core of the Moon is small, with a radius of about 350 km or less. This is only ~20% the size of the Moon, in contrast to the ~50% of most other terrestrial bodies." Which would make for a nice bell in space !

(Quotes from Wiki).

....Interesting ....

Cheers

[KenGee (Kenith Gee)]

Craig , your over reading what is says. It rand like a bell in the sense that the vibrations from the impact resonated through the moon. Your first point is a mix of facts spin to make an interesting story that one might over hear in a pub quiz night. Graviational anominals can be measured to create a gravity map, in fact that is high minerals like Iron are found on Earth. the movments of either statellites or planes are very, very small.

[CraigS]

Originally Posted by KenGee

Craig , your over reading what is says. It rand like a bell in the sense that the vibrations from the impact resonated through the moon. Your first point is a mix of facts spin to make an interesting story that one might over hear in a pub quiz night. Graviational anominals can be measured to create a gravity map, in fact that is high minerals like Iron are found on Earth. the movments of either statellites or planes are very, very small.

Hi Kenny;
Ok. That's cool. I did say that it may've been an urban myth ! (I think I remember I read it from a dodgy source).
It must've been pretty touch & go, navigating the early moon probes whilst in lunar orbit back in the 60s.

Point taken though, I'll try & refrain from quoting 'urban myths', (even if I do declare them as such), from now on.
I'm in total support of doing my best to keep this message board as 'urban myth free' as I can.

Cheers. Nice to meet you, too, by-the-way.