Several moons in the Saturn system

[Nereid]

There are lots of such wrt Jupiter; several moons in the Saturn system (3? 4? more??), and one wrt Neptune. There is also at least one asteroid that is in some kind of odd relationship with one of the stable Earth Lagrange points.

Is that it? Are there any good papers showing that the Saturn (and Uranus, and Mars, and ...) equivalent of the Trojans are unstable (in millions of years, or less), due to (for example) Jupiter? What about the Jupiter (and Uranus, and Neptune, and Earth, and ...) equivalent of Telesto/Helene/etc?

Should this thread be in Celestial Mechanics??

 

[Chronos]

This probably belongs in celestial mechanics.. which is visited less often than the crank page... The easy answer is captured moons are creatures of opportunity. Undoubtably, many have unstable orbits. Planetary science is not terribly popular these days. You might have to wait awhile before getting a solid answer.

 

[Garth]

I did some research on the evolution of the orbits of the Trojan asteroids some years ago The orbits of Trojan asteroids and came to the conclusion that they do not generally represent captured bodies but rather primordial ones. In other words they are remnants of the planetismals that formed the parent body trapped in the zones of stability around Lagrangian L₄ and L₅ positions.

GArth

 

[Labguy]

I did some research on the evolution of the orbits of the Trojan asteroids some years ago The orbits of Trojan asteroids and came to the conclusion that they do not generally represent captured bodies but rather primordial ones. In other words they are remnants of the planetismals that formed the parent body trapped in the zones of stability around Lagrangian L₄ and L₅ positions.

GArth

Seems to be the case. JPL new release today:
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=547

 

[Nereid]

Thanks fellow PFers ... moving to CM ..

 

[tony873004]

You can play around with trojans and experiment with their stabilities in different systems using a program I wrote called Gravity Simulator ( www.gravitysimulator.com). Trojans are best viewed using the rotating frame feature.

Try putting some trojans in the Earth / Moon system, and you'll see that they don't last too long because of the Moon's eccentricity, and the Sun's influence. Then, you can round out the Moon's orbit, delete the Sun, and watch them last indefinately. Or eliminate one or the other of these two perturbing elements to see how much effect each one has.

There's a few new realistic simulations I've recently added to the Gravity Simulator web page under the Simulations link.

You can see simulations of 3 sets of trojans in the Saturn system, (Dione & Helene), (Tethys & Telesto & Calypso), (Janus & Epimetheus).

I'll need to add Dione's newly discovered trojan after JPL Horizons makes its position and velocity vectors public.

A simulation for Earth's trojan, Cruithne, is included as well. Earth has another semi-trojan, 2002 AA29, that sometimes makes quasi-orbits around Earth. It is included in the Fullsystem simulation.

There's also a simulation called horseshoe, that traces out a textbook horseshoe orbit, but it is not stable in the long term.

Regarding Mars, I haven't tried it yet, but I would imagine that any Martian trojans would be unstable. If the Earth's Moon's trojans are unstable due to the Moon's eccentricity, and Mars has a similar eccentricity to the Moon, it probably can't hold onto trojans for very long.

 

[tony873004]

quoting myself

...I would imagine that any Martian trojans would be unstable...

I stand corrected. Mars has a trojan called Eureka (5261). It was discovered in 1990.

Here's a Gravity Simulator picture of Mars and Eureka sharing an orbit in a frame rotating with the peroid of Mars' orbit.