# The atmosphere and gravity of a cube earth

So I order a new earth from the planet builders at Magrathea, but somewhere along the way the specs get messed up so they make it a cube rather than spheroid. They use unobtanium reinforcements so it doesn’t collapse into a spheroid in a cascade of truly horrendous earthquakes, but don’t do anything about the weird distribution of atmosphere, or the large variations in gravity.

Assuming the same mass as regular earth, what would cubearth’s gravity be at the center of a face versus at a corner? (Let’s throw in the midpoints of the edges as well.)

And assuming the same amount of gasses as we have on earth, how would cubearth’s atmosphere be distributed?

Just a quick note to point out that at the points you choose – centers of a face, edge, and corner – the gravity will be directed toward the center, but it won’t at other positions on the surface of the cube. This will affect the way the water and atmosphere pools, but, in general, you’ll end up with “oceans” at the centers of each of the faces, and all the earth and anything else not nailed down to your unobtainium core will tend there, as well. At best, you might have beaches around those oceans. Since gravity doesn’t point either straight down to the center in most places, and is never normal to the surface (except at the exact center of each face), things are going to look very weird on your world. And the corners will be spectacularly high mountains, far, far huger than anything on earth, jutting far beyond the atmosphere.

It’s been four years, so it is time for another look at this.

*Another MM question!
*
Shortly, very shortly it will devolve into a common spheroid via violent earthquakes (cube quakes?) tidal waves, volcanic eruptions, etc. etc.

Wow. The death of the subjunctive form, in only four years.

Actually, if you stood in center face of the cube (assuming no ocean) wouldnt those actually and ironically be massively tall “mountains” you couldnt see/wouldnt notice?

To answer the question fully, you need to know the axis of any spin, and how the crust is supported by the unobtainium. Do we have a perfect cuboid crust, with no gaps or plates? If so, the only gravitational and spin effects will be on the surface rocks and layers, which might mean that they end up on all of the trailing edges of the faces. (Any force which moves them away from the centre will have less and less gravity resisting it until they hit the edge - and on average any force will be counter to the direction of spin).

You’d also get a big pile of stuff at the high-gravity centres of the faces - if the crust is rigid, this would be a pile, not an ocean. The fun thing is that it could be a bulge of water.

The same forces apply to the atmosphere, but with the increased pressure at points of high-gravity countering the clumping. I’m guessing the leading edges of the cube would have very low air pressure, with high pressure systems at the high-gravity points and the trailing edges.

Travel over an edge by any means would be problematic, to say the least.

Yep, since their sides are parallel to the direction of the horizon. But I can’t see massively tall mountains on the Earth that are hidden by the curve of the earth, either, so it doesn’t bother me.

Actually, I could see weird refraction effects due to changing density of the atmosphere in weird ways (it’s not going to be concentric with the “earth”) playing weird tricks with your perception. I’d have to sit down for a while and think about this. Refraction through the weirdly shaped atmosphere might actually bend the mountains into your line of sight. Or, alternatively, away from it. I’m just going to assume an airless sphere and me standing in the middle of the face.

Yes, but these would be mountains you’d NEVER notice being high no matter how close you were till you were on top. Then, at the top, you’d look down the other side and go oh crap! Well, you would notice an edge as you got close I guess. Pirate maps might be more accurate on this world.

Offhand, I dont think the atmosphere is going to do anything optically, because any line of sight towards the mountain is going to be perpendicular to any atmosphere/refraction gradient (I think).

Nope – the gravitational vector won’t be pointing toward the center of the cube earth, but it won’t be parallel to the surface, either. The atmosphere, like the ocean, is going to pool at the center of the faces. I don’t really know what shape it will have, but it’
ll be odd, and the effects wil be as well. I’m divided as to whether it’ll make the “ground” seem higher or lower than the horizon, but it’ll do something

That’s prevented by the unobtanium reinforcements, duh!

I actually figured it had been asked before, but skipped the search so as to have an excuse to delight new readers…

Yeah, I think your right there.

Near the center of the cube, unless you have an extremely clear atmosphere and can see A LONG way, I think things are gonna be close enough to parrallel/perpendicular to not have an obvious effects. As you moved towards the edge those conditions would start to fail I would think. Again, just off the top of my head.

Of course it your postulating a cube planet with unobtainum, I guess going with a perfectly clear atmosphere to boot is no biggy either.

By eating my post, the board has saved you all from a huge and wildly speculative post about Earth Cube plate tectonics, seasons, polar-face versus vertex-face models, axial tilt, and deep ocean currents. I don’t have the will to retype it all, so I will just leave you with this thought:

Adding a Moon Cube to a face-polar, untilted Earth Cube might conceivably produce enormous toroidal tidal bores at the center of each face, with the gravity gradient focusing the tidal flow in place of a river mouth.

Some good answers in this thread, and in the old ones, and funnily enough, I now recall reading this exchange way back when:

Golf clap.

For folks adding on here, the five+ pages in the previous three threads cover a lot of (oddly-shaped) ground. Good reading.

Similar thread in 2013: “Were the earth a cube…”

Me not know. But gravity be imperfect. Must be so.

I think I know what the global anthem of that planet would be:

Well, it’s just a box of rain
I don’t know who put it there…