When two planets are very close, what is the environment like?

So, I read the question, the associated answers and comments located here, as well as some others that were more divergent than what I was hoping for.

Basically, imagine two earth-like planets very close to each other and tidally locked. Say that there is something like 100 miles between them and some sort of magical\advanced technology structure is keeping the planets in this configuration:

What does this do to things like gravity, wind speeds, etc.? I would see gravity being close to being cancelled out on the surface, possibly with the effect of small, floating islands of material being possible.

How far would the effects be noticeable felt by those on the planets? What would weather patterns do in the area?

• Assuming they were locked by the north hemisphere, you would think much of the water on both planets would be pulled to the North. If it is the West hemisphere, water will be pulled there, etc. Assuming something like the picture in the linked question is possible (probably not) occupants would be walking and encounter a pretty solid wall of water. Just speculation and therefore is not good enough for an official answer though :) – JDSweetBeat Feb 12 '15 at 18:14
• @Dustin Jackson - I hadn't thought of that... I wonder just how rough seas like that would be and just how dry the other sides of the planets would be. – Brad Feb 12 '15 at 18:20
• I imagine any Ice (assuming the North/South) on the opposite side would stay. I am currently researching to find material for an answer. – JDSweetBeat Feb 12 '15 at 18:22
• For one author's take on this: Rocheworld – 2012rcampion Feb 12 '15 at 19:27
• Some people claim to be 'affected' by the presence of a full moon (something I find absurd), so I'm guessing they'd be moody all the time. – Mikey Jun 11 '15 at 17:02

The two planets would each have a ring of land around their 'equator', with a large ocean on the side pointing away from the other planet and another ocean connecting the two planets. Ships could probably be driven up this water bridge to get from one planet to the other.

This would happen due to the effective tides the two planets would apply to one another. The gravity of the other planet would pull one bulge up to what would probably be hundreds of miles in height, but since the planets are closer to this, the ocean would bridge the gap between them. On the opposite side of the planets, the inertia of the two planets spinning around each other would cause a similar bulge, resulting in a deep ocean.

The connective column of water would also be surrounded by enormous storms at all times. Since the planets are tidally locked, and orbiting extremely rapidly (given the low orbit altitude), the coriolis forces would be huge, and drive similarly huge storms, which would expand under the low gravity as the approached the connection point and then crash into each other, since they'd approach the connection point from opposite directions. (Storms on both planets would move in the same angular direction, clockwise or counter-clockwise, since the tidal lock effectively 'spins' both planets the same way).

Assuming the planets were both in the plane of the sun, the mega-ocean on the far side would spawn these storms, which would then tear across the land on the windward side of the ocean before hitting the connection point. The habitable portions of the planets would be towards the poles and on the leeward side of the far oceans.

This is all under the assumption that the planets won't warp under each other's gravity. They're well within the Roche limit for each other so tidal effects would normally rip the planets apart. We'll chalk that up to alien magic as well.

• Good answer. +1 for including the "Ocean Bridge" theory. – JDSweetBeat Feb 12 '15 at 18:23
• Do you think that the 'connecting area' would get cold enough to start having ice form? I would assume that the area would get much less light, thus heat, than it would normally. And I think that such an "Ocean Bridge" would make the southern tips of South America and Africa seem like vacation sailing spots, too... – Brad Feb 12 '15 at 18:26
• I'd still like to see your potential answer, Dustin, before marking anything as an answer. – Brad Feb 12 '15 at 18:50
• The bridge might be cold, but it wouldn't freeze. The same coriolis effects that are driving the huge storms would push massive currents through that area, drawing in water from warmer regions. It's also possible that, depending on the amount of water on the planet, the Coriolis currents could connect the two oceans on each planet into a ring around the equator. – ckersch Feb 12 '15 at 18:58
• @insanity The two planets would be tidally locked. Even if this were not the case initially, there would be a lot of friction slowing down the rotation of the planets relative to each other. They would orbit one another in a configuration where the same face of each planet would always point towards the other planet, with a day length equal to the orbital period of the planets around their common center of gravity. – ckersch Mar 15 '16 at 15:39

The two worlds would form an "egg" shape and the entire planet would deform into this shape. At the surface you would not get zero gravity or things flying towards the other planet. Counter-intuitively you would feel exactly the same net force (gravity+centripetal) at every location on the surface of the planet, and the planet would change shape to match that with only localized variation such as hills or mountains.

Can an atmosphere englobe a planetary ring?

Could two planets be tidally locked to each other so close they share their atmosphere?

This discussion:

http://chat.stackexchange.com/transcript/message/18052695#18052695

Which continues here:

http://chat.stackexchange.com/transcript/17213/2014/10/8/13-21

And this sketchtoy:

http://sketchtoy.com/63271225

You can see the initial misconception (where zero-g would be) and then the correction.