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Posted by: spaceffm Nov 14 2005, 10:22 PM

I thought about it a lot.
Do U think it would be possible that Earths gravity catches someday an asteroid or something similar and would keep it as 2nd moon?

What precondition would be absolutly necessary?
WQould it be possible at all due to both gravitational fields of earth and moon?

Wouldn't it be fantastic to have a 2nd small moon?

Thx for sharing your thoughts in this matter...

Posted by: djellison Nov 14 2005, 10:35 PM

We have one called Cruithne I believe - something like that

Doug

Posted by: BruceMoomaw Nov 14 2005, 10:36 PM

It would certainly be possible, thanks to three-body gravitational effects -- that is, the gravitational effect of the Sun slows down the rate at which an asteroid passes the Earth (during their separate orbits around the Sun) to the point that it can drift into orbit around Earth without the need for any disturbing impact or friction. But this requires very specific conditions; the zone in which it can take place is seriously limited.

Still, it does happen -- Jupiter, whose three-body capture zone is much wider, regularly captures comets as temporary satellites in highly elliptical orbits and and then releases them at a later apoapsis. (In the case of Shoemaker-Levy 3, one such comet actually crashed into Jupiter at its periapsis, although that happens only about once a millennium.) And I seem to remember reading somewhere calculations that one small near-Earth asteroid may have been briefly captured a few centuries ago. The possibility cannot quite be ruled out yet that our own Moon was captured that way, rather than being created by the debris from a glancing impact -- Harrison Schmitt, at any rate, is still holding out for that alternative theory. But the odds, to repeat, are very long.

Posted by: BruceMoomaw Nov 14 2005, 10:38 PM

Cruithne, however, isn't a "moon", but just an asteroid locked into a 1:1 orbital-period resonance with Earth ( http://burtleburtle.net/bob/physics/cruithne.html ). Also, it's Shoemaker-Levy 9 -- not "3" -- that hit Jupiter.

Posted by: Bob Shaw Nov 14 2005, 10:43 PM

A couple of years ago there was a brief flurry when a second 'moon' did turn up - it turned out, however, to be the S-IVB stage from the Apollo 12 Saturn V, which had entered Solar orbit and been recaptured within the Earth-Moon system (not on a permanent basis, however). In true scientific detective-novel fashion, it was discovered to be the spent spacecraft booster as a result of spectral analysis, which revealed a surface coating of, er, Titanium Oxide - as in white paint!

Bob Shaw

Posted by: tasp Nov 15 2005, 03:09 AM

Toro!

Funny little asteroid that was in resonance with Venus, and now is in a resonance with Earth.

Yet another way objects can have relationships in our amazing solar system.

Posted by: silylene Nov 15 2005, 03:28 AM

Two other asteroids, 1998 UP1 and 2000 PH5 are also locked into resonance with Earth, with orbits not unlike Cruithne.

Posted by: mike Nov 15 2005, 05:29 PM

Some might say that Earth is Cruithne's moon.

Posted by: ljk4-1 Nov 15 2005, 05:57 PM

A couple of years ago there was a brief flurry when a second 'moon' did turn up - it turned out, however, to be the S-IVB stage from the Apollo 12 Saturn V, which had entered Solar orbit and been recaptured within the Earth-Moon system (not on a permanent basis, however). In true scientific detective-novel fashion, it was discovered to be the spent spacecraft booster as a result of spectral analysis, which revealed a surface coating of, er, Titanium Oxide - as in white paint!

Bob Shaw

Posted by: blobrana Dec 6 2005, 08:17 PM