Situations that generate unusual planetary conditions

[Slarty]

I am looking for strange and interesting planetary circumstances for basing a board game around.

This can involve any configuration of planetary bodies and their environments, but must be at least a theoretically possibility in general terms. Perhaps it would be best to illustrate with some examples:

A planet with an atmosphere gravitationally locked to its sun. One side freezing cold the other side boiling hot with a moderate twilight zone in between, perhaps with Volcanism on the dark side that stops the atmosphere from completely freezing (I saw the recent thread on this).

2 planets in very close proximity orbiting around each other with tidal wave tides.

Large Asteroid impact onto a planet excavating a huge and very deep crater, (how deep could it be for a roughly Earth sized planet?) providing the potential for unusual conditions (flooding/exploration).

I want to keep things broadly realistic but would accept some wriggle room for a really interesting ideas!

 

[mfb]

A planet with an atmosphere gravitationally locked to its sun.

That gives a large global wind system. If the atmosphere is thick enough, temperatures are fine.

A double planet in a very close orbit would be tidally locked, but I think this can give interesting effects as well. One side on each planet would give a great view of the other side.

An asteroid impact so large that it produces a permanent deep crater is probably deadly for life on the surface.

A planet, spinning so rapidly that it nearly breaks up? Would give a very low surface gravity and (if you like) strange day cycles/seasons.

An earth-sized moon in the orbit of a gas giant?

A planet in a system of multiple stars... there are many options how to implement this.

 

[Slarty]

A planet, spinning so rapidly that it nearly breaks up

A planet, spinning so rapidly that it nearly breaks up? Would give a very low surface gravity and (if you like) strange day cycles/seasons.

Interesting idea. I wonder how fast it could rotate and what would be the limiting factors? Presumably there would be a gravitational gradient on the surface from pole to equator? If a planet was spinning fast enough would it be possible for it to slowly stretch out into a flattened sphere and eventually into something resembling a discus?

 

[mfb]

Haumea shows something similar. You don't get something as flat as a discus, but something between a discus and a sphere is possible.

I wonder how fast it could rotate and what would be the limiting factors?

Surface gravity at the outermost part has to be positive, otherwise the system breaks apart. As surface gravity depends on the shape, and the shape depends on surface gravity, this is not so easy to determine, but anything big enough will be in some hydrostatic equilibrium.

Presumably there would be a gravitational gradient on the surface from pole to equator?

Right

 

[Slarty]

permenant crater from asteroid impact

"An asteroid impact so large that it produces a permanent deep crater is probably deadly for life on the surface."

Probably true I fear, however a spaced based observer could see it and presumably at some point after the immediate fire ball would be able to explore the surface. So from a physical perspective what would limit how deep the crater could be assuming an Earth type world and a strike into the center of a large continent so no catastrophic immediate flooding.

 

[mfb]

A deep crater ("air") is lighter than the material outside - the crust would go up at that point to restore the balance. This is eased by the fact that the impact melted and heated a lot of material.
I would expect that the maximum is a few km below sea level.

 

[cephron]

Re: deep crater--what if the planet was tectonically dead? Would the crater still get filled in?

Speaking of which, a tectonically dead planet would present a whole lot of interesting situations, the first of which is--correct me if I'm wrong--no magnetic field to shield the surface from radiation (or to tell which way north is). Also, depending on how long ago it went dead, there would be geological implications because there would be no more "building up" effects to cancel out with erosion. The surface would only get flatter, barring deliberate human/sentient activity.

In a tectonically dead planet, I think you would theoretically be able to dig as deep as you want--even to the very core of the planet. The feeling of gravity would decrease as you went towards the center, but pressure (air pressure, water pressure, pressure needed to hold tunnels open) would build to extremely high levels. I'm sure there are other things I haven't thought of...

 

[mfb]

This happens independent of tectonic activities, it is sufficient to have molten material under the crust. If the crust of the planet is very thick, a deeper hole might be possible, but then you have a very flat surface and probably no dry land (if water or another liquid is present).
It cannot be TOO deep, however - even "solid" material will begin to flow, if the pressure is high enough.

 

[brenan]

A planet, spinning so rapidly that it nearly breaks up? Would give a very low surface gravity and (if you like) strange day cycles/seasons.

Interesting ideas.

Your biggest issue would be what made it accelerate to that speed in the first place and
why isn't it slowing down? Presumably you wouldn't be able to get anywhere near it.

If the planet is spinning so is it's atmosphere.
If it isn't spinning it's dead.

A big crater is possible but get too big and the planet is either rubble or in a very strange orbit.
The size of the planet - distance from sun (of certain type), rotational speed, density and make-up , and (I read in one briefing some time ago) a moon of just the right size are all requirements for planets humans would be comfortable on.

Think of the issues with a very similar planet to Earth such as mars. You may want to go and do
research (actually a very good idea) but you wouldn't want to permanently live there except
in a tightly enclosed environment. You can do that on Earth so there isn't much point.

Our kind of life needs pretty specific circumstances to be happy.
Other kinds of life would need other specific circumstances.

Ringworld is a very clever redesign of essentially the same factors just manipulated
to match the same conditions physically.

Perhaps something like that could be worked out - varying just enough to build
a "pleasure planet" for explorers or something. Too much variation would make
it a fantasy planet though.

 

[Slarty]

permenant crater from asteroid impact

I suspected that the crater idea might be a bit limited in that anything too deep would uncover hot material that would be heated further by the impact and melt - filling the hole. Is there any other astromonic or geologic mechanism that could create a very wide deep crater other than an impact?

 

[mfb]

Your biggest issue would be what made it accelerate to that speed in the first place and
why isn't it slowing down? Presumably you wouldn't be able to get anywhere near it.

It can gain angular momentum from impacts of asteroids during its formation. Without large moons, there is no reason why it should slow down, neglecting asteroid impacts afterwards.

If the planet is spinning so is it's atmosphere.

So what?

If it isn't spinning it's dead.

What is dead?

A big crater is possible but get too big and the planet is either rubble or in a very strange orbit.

The orbit won't change much from any impact not melting the whole crust.

The size of the planet - distance from sun (of certain type), rotational speed, density and make-up , and (I read in one briefing some time ago) a moon of just the right size are all requirements for planets humans would be comfortable on.

And a cactus needs a desert. This does not mean a rain forest does not allow life.