Can this planet exist?

[William_Congreve]

I was thinking about a theoretical planet/moon, and I wanted to know if it could actually exist or if there was some inherent problem with it. I figured that you people could probably answer my question.

Anyways, the basic concept of the planet is that it rotates faster than an orbit infinitely close above the surface would travel.

Obviously anything on the surface would be flung off so there would be no dust, atmosphere or rocks, and it would probably have to be made of some strong metal. Also I'm not sure how it got to be spinning so fast, but I'm just interested in if there is a problem with a planet like this theoretically, not whether it's realistic for it to exist or not.

Things I figured out about the planet (feel free to tell me I'm wrong):

A: It would be nigh-impossible to land on. You would expend massive amounts of delta-V because you would have to 1. speed up to be at its surface speed 2. manipulate your path as you flew so as not to zoom off into space. I think you'd be burning down and prograde unlike a regular landing retrograde and up. You'd also have to tether your ship and yourself down.

B: Standing in a cave inside it, the center of the planet would be above your head because centripetal force would be greater than gravity.

C: It would be trying to fling itself apart, so it would have to be very strong.

D: Small asteroids that are spinning fast are this already, but they aren't interesting because they have so little gravity.

So anyways let me know if a planet like that can't exist for some reason, or if you can figure out something else interesting about a planet like this.

[Kerbin Dallas Multipass]

A planet like this cant form I'd say. With planet I mean a planet sized object.

-Planets form because matter (basically gravel, dust, gas) settles down around a center of gravity.

-But let's say we already have a sturdy planet and want to make it spin. To make it spin that fast we need a huge impact. A huge impact would create heat and melt or break the stuff the planet is made of. Stuff would just fly off. No more planet.

-Even if you take a theoretical frozen bowling ball the size of a planet, I would guess that - at that scale - it would stretch out like rotating pizza dough and just fly apart.

Just my 2cts. Maybe someone has better imagination and knowledge

[NovaSilisko]

You could get it ALMOST at orbital velocity, but not at or above. At the scale of a planet, rocks tend to start acting more like fluids (well, crunchy fluids, but you get the idea. Io, for instance, is solid on the surface but is squashed and stretched by tidal forces). It would just shed and redistribute material until it was at a level below orbital velocity.

Landing on a body with its surface moving at nearly orbital speed though is almost laughably easy. All you really do is just perform an orbital rendezvous with the ground, and make sure you're feet-first when you come down.

[Z-Man]

And hold on real tight, because it is rotating *faster* than orbital speed.

Or you could simply land at a pole. No problem there.

And yes, no way such a thing could form in reality or even exist made out of known materials. No, it would not fly apart (provided the rotation speed is well below escape velocity), but burst and rearrange itself into a flat ellipsoidish thing.

Objects that get close do exist, though. Look up Millisecond Pulsars. Still, nothing you would want to land on

Edit: Though I guess we all do not quite understand your question. What, exactly, is your definition of "theoretically"? You seem to already be aware of the practical issues, so which limits of reality do you want to ignore? If you want to ignore limits on real materials' strength, then yes, it could exist, no problem, but never form naturally. If you want it to be made (literally, i.e. built to order for an weird 10^18-ionare) of the strongest material possible, then also yes, it could exist, but only if it rotates just a tiny bit faster than orbital speed, and it would need to be pretty disk-shaped.

Edited January 9, 2014 by Z-Man

[Stargate525]

The only thing that could come close is a pulsar, and those are made of stuff that barely qualifies as atoms anymore.

[magnemoe]

The only thing that could come close is a pulsar, and those are made of stuff that barely qualifies as atoms anymore.

Pulsars has insanly strong gravity so they can spin fast. Many small asteroids rotate faster than their puny gravity allows for but are solid rocks they also don't need to spin fast as their gravity is less than 1/100 of an g

[William_Congreve]

Edit: Though I guess we all do not quite understand your question. What, exactly, is your definition of "theoretically"? You seem to already be aware of the practical issues, so which limits of reality do you want to ignore? If you want to ignore limits on real materials' strength, then yes, it could exist, no problem, but never form naturally. If you want it to be made (literally, i.e. built to order for an weird 10^18-ionare) of the strongest material possible, then also yes, it could exist, but only if it rotates just a tiny bit faster than orbital speed, and it would need to be pretty disk-shaped.

Thanks for all the great replies, everyone . To answer your question, Z-man, I want to ignore how things realistically form. I'm wondering if a planet like I suggested would be stable, not how hard it would be to make.

[DisarmingBaton5]

You could land at the poles or grapple (KAS style) onto the equatorial surface. As Zman says, though, the planet would probably not exist.

[peadar1987]

Well it certainly wouldn't form rotating that fast, as if the rotational force is greater than the gravitational, the planetary nebula will be spun off into space instead of coalescing into a planet.

Some catastrophic event causing the rotation after formation? Maybe, but it would have to be made of incredibly strong material to have that sort of rotation given to it without being obliterated.

[lajoswinkler]

No, it can not exist because the material which piles up when the planets are evolving will not pile up if the speed of each component is at the escape velocity of the whole pile. At best you can get a body with almost 0 G at the equator, but if you account for the fact NovaSilisko mentioned (at huge scales, solids behave like very viscous fluids), you get internal friction, heating, distortion. All that consumes the energy and releases it as heat. Rotation slows down.

One even more possible scenario is global stratification, where the less dense material collects on one side and a bulge is formed which would partially detach from the body and turn into a satellite.

Fragment from a large impact upon a bigger, heterogenous body are a candidate. Those would be small asteroids with lots of nickel and iron. They could spin fast enough.

Anything larger and you get viscosity.

There are two examples of similar, fictional, bodies that I know about. Mesklin, from Hal Clement's novels, which is a very large, rocky, very oblate planet with short rotation period. 3 G at equator, almost 300 G at poles.

Inaccessable, body in Krag's Planet Factory.

http://forum.kerbalspaceprogram.com/threads/60318-Krags-PlanetFactory-Updated-Dec-3

Manley made a video about it, and he spent a lot of it explaining how things work, specifically how the rotational reference frame is weird, something which is obvious when you try to land on Inaccessable.

Edited January 9, 2014 by lajoswinkler

[MBobrik]

If it rotates faster than its surface orbital velocity then the centrifugal force is stronger at the equator than the force of gravity.

Of course a solid monolithic object can hold itself together by the tensile strength of the rock.

However a planet has to be big enough to assume spherical shape by reaching hydrostatic equilibrium. Otherwise it does not count as a planet by definition.

and something can not stay at hydrostatic equilibrium when the forces pulling it apart are higher than the forces pulling it together.

.

So you can have (small) asteroids spinning at rates high enough to negate the surface gravity, but you cant' have planets spinning like this by the very definition of the word "planet".

Edited January 9, 2014 by MBobrik

[Stargate525]

Well, you COULD...

Hydrostatic equilibrium just means the planet is balanced between gravity and outward pressure; you could do that by having an incredibly wide planet. Spin it fast enough, and your planet turns into a discus, but it's still a planet.

[MBobrik]

Well, you COULD...

Hydrostatic equilibrium just means the planet is balanced between gravity and outward pressure; you could do that by having an incredibly wide planet. Spin it fast enough, and your planet turns into a discus, but it's still a planet.

sure, you can have a highly flattened planet. but you cant' have a planet where the centrifugal force is bigger than the gravity because it would fly apart.

[Raven.]

Well, you COULD...

Hydrostatic equilibrium just means the planet is balanced between gravity and outward pressure; you could do that by having an incredibly wide planet. Spin it fast enough, and your planet turns into a discus, but it's still a planet.

A planet like this is theoretically possible if it had a strong enough gravitational field to hold it together. But we're talking about an enormous amount of kinetic energy here. Asteroids are able to spin fast because it takes a much smaller amount of kinetic energy to drive that kind of mass. We're talking about an object much more massive than an asteroid. More mass equal more kinetic energy. This planet just simply is not realistic due to the enormous amount of kinetic energy involved. Not unless there was some kind of catastrophic event.

[TechnicalK3rbal]

It probably couldn't form, however, if you somehow created a giant stone sphere, it would probably work.

[Stargate525]

A planet like this is theoretically possible if it had a strong enough gravitational field to hold it together. But we're talking about an enormous amount of kinetic energy here. Asteroids are able to spin fast because it takes a much smaller amount of kinetic energy to drive that kind of mass. We're talking about an object much more massive than an asteroid. More mass equal more kinetic energy. This planet just simply is not realistic due to the enormous amount of kinetic energy involved. Not unless there was some kind of catastrophic event.

But he's not arguing possibility of formation, he's arguing possibility of EXISTENCE. It can be done. You could dump enough energy into a body's rotation to get it up to those kind of speeds.

I don't know why a civilization would WANT to...

[lajoswinkler]

But he's not arguing possibility of formation, he's arguing possibility of EXISTENCE. It can be done. You could dump enough energy into a body's rotation to get it up to those kind of speeds.

I don't know why a civilization would WANT to...

It can not be done with a naturally made planet. It would fall apart. Even if it's a huge artificial body, rotational energy would dissipate on friction because of the unavoidable fluidity of solids on large scales. I don't know how long would it take, though.