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Tom Mazanec
2004-May-14, 02:57 AM
Can planetary moons have natural satellites?

ToSeek
2004-May-14, 03:17 AM
The orbits are probably not stable over the long term due to the influence of the larger parent body. I'm sure someone else on here will chime in with a more rigorous analysis.

kenneth rodman
2004-May-14, 06:56 AM
im not a scientist or such but i dont see why not. Im thinking they would be 2 moons orbiting each other and both those moons would orbit the planet

Kullat Nunu
2004-May-14, 10:28 AM
im not a scientist or such but i dont see why not. Im thinking they would be 2 moons orbiting each other and both those moons would orbit the planet

I don't think that would be stable.

If the satellite is massive and orbits very far away, a small sub-satellite might be possible on low orbit.
On the other hand, small disturbances could easily throw the sub-satellite from its path.

Avatar28
2004-May-14, 01:58 PM
im not a scientist or such but i dont see why not. Im thinking they would be 2 moons orbiting each other and both those moons would orbit the planet

I don't think that would be stable.

If the satellite is massive and orbits very far away, a small sub-satellite might be possible on low orbit.
On the other hand, small disturbances could easily throw the sub-satellite from its path.

Okay, how about this. The earth's moon is relatively massive compared to it's parent body. Could our moon have it's own natural satellite if it were in a relatively low orbit?

Kullat Nunu
2004-May-14, 02:16 PM
Okay, how about this. The earth's moon is relatively massive compared to it's parent body. Could our moon have it's own natural satellite if it were in a relatively low orbit?

No. I think the Sun (and Earth?) would perturb the satellite too much.

Can a tidally locked body have a satellite anyway?
I mean not mutually locked like Pluto.

Taibak
2004-May-14, 02:47 PM
The orbits are probably not stable over the long term due to the influence of the larger parent body. I'm sure someone else on here will chime in with a more rigorous analysis.

Well... can't you make the same argument about planets? The Earth is relatively close to the Sun and it has a moon. I don't see why you couldn't have a moon orbiting far enough away from its planet to have its own satellite. Or, put another way, are there still artificial satellites orbiting the Moon? If so, why couldn't a small natural satellite sit in a similar orbit?

My big objection would be how that satellite got there in the first place. To me, it seems unlikely that it would form in such an orbit and it would be equally unlikely for it to be captured by the moon and not the planet.

daver
2004-May-14, 04:20 PM
Okay, how about this. The earth's moon is relatively massive compared to it's parent body. Could our moon have it's own natural satellite if it were in a relatively low orbit?

This came up quite a while ago in another group; the upshot was that there are no long-term stable orbits around the moon. If you're too far away, perturbations from the earth and sun quickly take you out of orbit. If you're too close, the mascons (mass concentrations) perturb you into a surface-intersecting orbit.

aurora
2004-May-14, 04:45 PM
I seem to recall a couple of moonlets, of Saturn?, that swap orbits periodically. Not exactly the same thing as a moon with a moon, but is an example of two moons that are gravitationally connected.

AZgazer
2004-May-14, 06:24 PM
My thoughts are this could only be possible if you had 3 extremes.

1) Planet and Satellite are as close in mass as possible.
2) Satellite orbits as far as possible to still maintain a stable orbit.
3) Sub-satellite has the smallest mass possible to maintain low orbit.


Note my statement was not absolute. :cry: If there are problems with physics laws please point them out. :)

SiriMurthy
2004-May-14, 07:15 PM
Can planetary moons have natural satellites?
The system can be stable if the sub satellite has a polar orbit. But it is very rare for a natural system to have a body in polar orbit.

umop ap!sdn
2004-May-16, 08:46 AM
Wouldn't it eventually get pulled out of polar orbit anyway? Most of the moons tend to align roughly to either the ecliptic or their planet's equator (even Uranus :o ) and the ones that line up to the equator orbit closer, so it seems as though some (tidal?) force is causing them to do so. Anyway whatever the cause I think the same thing would happen in orbit around a moon.

Kullat Nunu
2004-May-16, 10:09 AM
I think cityboy916 is right. Polar orbits are not stable in the long-term.

Actually, this page (http://www.astro.ubc.ca/people/gladman/jup2003.html) claims that one of Jupiter's newly-found irregular satellites, S/2003 J 20 (incination 55.1), has almost the greatest inclination possible (due to the Kozai resonance, I have no idea what that means :-s ).

And, of course no satellite can form in a very inclined orbit; all large satellites besides Earth's Moon and Neptune's Triton are tought to have formed around their mother planets.

bobjohnston
2004-May-17, 02:27 AM
This came up quite a while ago in another group; the upshot was that there are no long-term stable orbits around the moon. If you're too far away, perturbations from the earth and sun quickly take you out of orbit. If you're too close, the mascons (mass concentrations) perturb you into a surface-intersecting orbit.

Good point. This is illustrated by the stuff we left in lunar orbit in the 1960s: much of it has already impacted the Moon.

Ilya
2004-May-18, 03:46 AM
Good point. This is illustrated by the stuff we left in lunar orbit in the 1960s: much of it has already impacted the Moon.

All of it, actually.