Re: Solar system building

Erik Max Francis wrote:

Mark L. Fergerson wrote:

ISTM it won't work with two planets of very different sizes
because the bigger one would just capture or eject the
smaller, but so what? With nearly equal-size planets there'll
still be a worldwide eclipse, and the onset/release of tidal
forces during the swap should provide the desired quakes.

Yes, coorbitals only work with similarly-sized objects. They
have to swap orbits as they interact, so they have to affect
each other's orbits similarly. A gas giant and an Earth-sized
planet wouldn't work.

They don't have to be really close in size. Janus is about 4
times as massive as Epimetheus and that arrangement is stable.
However, it means that Epimetheus changes its orbital distance
from Saturn by four times as much as Janus does when they swap.
I'm not sure if there's an actual limit to the mass difference.
Note that Earth has a vaguely similar arrangement with the
asteroid Cruithne, and the mass difference there is immense. (
http://en.wikipedia.org/wiki/3753_Cruithne )

Note also that when they do swap orbits, they don't eclipse one
another. The planet approaching from behind will speed up as it
gets closer which moves it into a higher, slower orbit and the
opposite happens to the other planet. From the point of view of
someone on one planet, the other will be seen as making a U-turn.


As for that idea working, the tidal forces will be greatly
increased during their closest approach, but I'm not sure it
would qualify as enough to cause major quakes on either world.
Greatly increased tides with bad consequences, maybe.
Civilization-affecting disasters, I'm not so sure.

Yes, they're not likely to approach more closely than a few
million Km (Cruithne never gets closer than 12.5 million Km) so
astronomically induced seismic activity is unlikely.

--
Dan Tilque


.

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