Re: Close Orbiting Planetoids Sharing Atmospheres

Mike Williams wrote:
Wasn't it who wrote:
The egg thing though... I like that. Definitely letting them have that.
Moons are gonna be teeny and in Lagrange points, and the atmosphere
sharing will be nominal atmosphere falling/flowing in between the
shared gravitational influence that distorts the tidally locked worlds
into eggs. If that would keep them from crashing together, it is kept.

I suspect that the two egg-shaped planets have to be pretty much
identical for the atmospheres to be linked and breathable. I think that
if the surface gravity on planet A is 0.15% greater than that on planet
B, then the atmosphere will get sucked off B onto A, leaving planet B
with an atmosphere like that on the top of Everest. [Gravity at the top
of Everest is 0.15% less than that at sea level]

Rocheworld by Robert L. Forward has already been mentioned in this
thread, and I can only second that recommendation and elaborate on it. :)

The two "lobes" of Rocheworld orbit each other with a separation of just
a few tens of kilometers between their inner points. One is very
slightly smaller than the other, which was equivalent to its surface
being a few kilometers lower in "elevation" (height above an imaginary
plane of gravitational equipotential). This caused water to
preferentially collect on that lobe, so one of the two bodies was an
ocean world and the other was a desert.

There was a superjovian planet in Rocheworld's solar system that
Rocheworld's orbit brought it close to once a year and the tidal
interaction between Rocheworld and the gas giant caused the two bodies'
orbits around each other to contract slightly. During the few days of
closest approach this resulted in some of the ocean "overspilling" the
gravity of the water-rich lobe and forming the most gigantic waterfall
the galaxy has likely ever seen. Over the rest of the year the added
water evaporates from the desert lobe and rains back out on the water lobe.

Forward is a physicist who always paid very close attention to the
physics of his books, so I'm willing to bet that this arrangement is in
fact quite possible. Unfortunately he wasn't so good at plot and
characterization so the book isn't a great work of literature, but the
setting is certainly one of the more interesting bits of worldbuilding
I've seen.

Oh, also elsewhere in the thread there was suggestion of putting things
at the L4 and L5 points of the double planet. Lagrangian points require
that the two main bodies generating them have very different masses,
when their masses are similar the points are no longer stable. So these
dual worlds aren't going to have stable L4 and L5 points.
.

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