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View Full Version : How many moons does the Earth have?



Edwin
2003-Nov-21, 08:58 AM
We have the moon and lots and lots of artificial satellites but do we have any more natural satellites? Zephyr46 pointed out that we could have 5. Could there be more.
If a natural satellite were to orbit both the moon and the Earth ( an elongated path encompassing both objects) what would it be classified as then?

Josh
2003-Nov-21, 10:52 AM
I know of at least one other natural satellite of Earth. It isn't in Earth orbit all the time though. I'll try to find some stuff on this and get back to you...

Josh
2003-Nov-21, 11:35 AM
Here you go ... a Space.com (http://www.space.com/scienceastronomy/solarsystem/second_moon_991029.html) article.

Matthew
2003-Nov-22, 08:09 AM
Well tiny rocks in an orbit could be a 'natural satellite'.

So really first we need to work out what a 'moon' is before we can ask.

Edwin
2003-Nov-22, 09:25 AM
Can we really define what a moon is? My own defanition is that it should permanently orbit it's planet or asteroid. Cruithne doesn't. It bounces back and for orbiting our path so to speak but a lot of the time it is no where near us (if I understand the article correctly)

zephyr46
2004-Nov-13, 03:01 AM
Just for the record, Club AU (http://www.hohmanntransfer.com/topics.htm#taxon), is the article on the co-orbital asteroids.

I would like to call 3753 Cruithne a moon, but it is not, it is a co-orbital asteroid, it shares our orbit.

La Luna or Selene or more traditionally, the Moon, is the Earths only know natural satelite. If there were found to be a grain of dust orbiting the earth, it to, would be a moon. A notably less substantial moon, but a moon, none the less.

Unless it was reflected into orbit by a passing interplanetary probe, then it would be space related debris I guess :) .

The argument about moons and captured asteriods is pretty superfluous
to me, they are natural satelites, therefore moons.

If we come up with a solid model of planetary formation, we may impose a specific requirement that a moon be a co-forming component with its orbital companion. In which case 1999 CG9 (http://www.hohmanntransfer.com/cat/astu.htm#au1999cg9) is in a very interesting position (providing it isn't a rocket booster :D ).

I love this stuff!

Betelgeuse
2004-Nov-13, 09:22 AM
Originally posted by Ed J@Nov 22 2003, 09:25 AM
Can we really define what a moon is? My own defanition is that it should permanently orbit it's planet or asteroid. Cruithne doesn't. It bounces back and for orbiting our path so to speak but a lot of the time it is no where near us (if I understand the article correctly)
There are some good definitions of natural satelites here (http://www.google.co.uk/search?hl=en&q=define%3A+satellite&meta=).

Earth could very well have other natural satelites. Josh has introduced us to "cruithane" a 3 mile (5 km) object in a horseshoe orbit around Earth - a period of 770 years. It was discovered in 1986, but it took a lot of observations in order to figure out its complicated orbit, which was determined in 1997.

It's worth reading the press realease Josh's suggested.

It's worth thinking about the fact that other moons will affect the tide on earth - more than one tide per day, or a less regular cylce of tides. Of coure there would be more solar eclipses and seasesons etc will be affected.

Matthew
2004-Nov-20, 03:39 AM
Rigel any other "moon" that we don't know about will probably not be big enough to effect the tides or cause a solar eclipse. Of course a moon would affect the tides, but in such a miniscule manner it isn't relevent.

rahuldandekar
2004-Nov-20, 06:24 AM
Jupiter has a whole body of such moons . ( I would suggest we call them satellites). Some comets never go far beyond Jupiter. They can be called satellites of jupiter.

Earth is much smaller in size than Jupiter, but it may have a family of small asteroids.

suntrack2
2004-Nov-20, 04:39 PM
the dinassaur has gone, some lakes and big vallies made it may be due to the big asteroid fall in the past,
may be they were the moon of the earth in past history, this one is we are looking with our eyes, still today.

sunil

Betelgeuse
2004-Nov-20, 06:10 PM
I agree Mathew, I hadn't thought about it like that before, however, what my hypothesis was suggesting is, if there were many natural satelites - hundreds and hundreds of them, all in the same orbit it's worth suggesting that there would be enough gravity between them to effect the tides. I see how unconventional this actually is.

This of course is very unlikely, and thanks for your correction, Mathew!

Regards
Rigel