Hoopworld

eburacum45 · Post #1by **eburacum45** » 18.05.2006, 11:00

Grant Hutchinson has found some equations which suggest that a toroidal planet might be stable under a very limited set of circumstances; I've made an example of one such in Celestia

The parameters of this world are (according to Grant)
For a major radius of 70,000 km
a minor radius of 2000km gives a surface acceleration 0f 9.8 m/s??, a mass of 3x10e25kg and a rotation period for stability of 25.9 hours.

Surface area eleven Earths, mass five Earths, if my own maths are correct.

PlutonianEmpire · Post #2by **PlutonianEmpire** » 18.05.2006, 22:21

what's the difference between that and ringworld?

Johaen · Post #3by **Johaen** » 19.05.2006, 00:06

PlutonianEmpire wrote:what's the difference between that and ringworld?

Correct me if I'm wrong, but I'm pretty sure that with ringworld, the living space is on the inside of the ring, while with hoopworld, the living space is on the outside of the ring.

PlutonianEmpire's sig wrote:My computer: Dell Inspiron 8600, 60 gig hd, 256 meg ram, 1400 megahertz processor w/a speed of 1.37 gigahertz, Nvidia graphics card, and Celestia 1.4.1pre1.

I'm sorry.

PlutonianEmpire · Post #4by **PlutonianEmpire** » 19.05.2006, 01:09

ahh, i see now. thanks

sorry for what?

Malenfant · Post #5by **Malenfant** » 19.05.2006, 04:34

Looks like the living space is on *both* sides of the torus in the picture.

I'm presuming Dollan meant that this is supposedly stable as an artificial arrangement, not that toroidal planets can somehow form naturally.

Johaen · Post #6by **Johaen** » 19.05.2006, 12:47

Hmm... now that I've actually clicked the little thumbnail to see the full size image, I see that the living space is on the entire surface of the hoop, kinda like painting an Earth texture on a hoola-hoop.

And I was just apologizing for your computer. It just sounds kinda crappy to me. But hey, as long as it works

Dollan · Post #7by **Dollan** » 19.05.2006, 13:36

Malenfant wrote:Looks like the living space is on *both* sides of the torus in the picture.

I'm presuming Dollan meant that this is supposedly stable as an artificial arrangement, not that toroidal planets can somehow form naturally.

You are correct, though it was actually Steve saying this, not me... :wink:

...John...

eburacum45 · Post #8by **eburacum45** » 19.05.2006, 18:32

Yes; the entire hoop is habitable; gravity is perpendicular to the surface over its entire surface.
Here is the thread at Badastronomy where Grant finds the specifications for this object; and where the limitations of such an object are discussed.
http://www.bautforum.com/showthread.php ... post746219

Someone with the unusual name of Mugaliens is evidently going to model the behaviour of such a torus on a supercomputer.

steve

Rassilon · Post #9by **Rassilon** » 20.05.2006, 18:46

Interesting variation on the ringworld concept... I would be interested in the orbital and procession parameters of such an object... I suppose that with gravitational forces related to regular planets could such an object have a tilt? Because if it didnt then I would consider the inner ring to be an arctic wasteland! or uninhabitable.... It would almost need a tilt of 45 degrees wouldnt it?

Post #10by **selden** » 20.05.2006, 19:00

I'd think the inner side could be like being more or less near the pole of a spherical planet.

Any tilt at all will produce day/night effects on the inner side. It's just that with small tilts the night is much longer.

And there are the "polar" regions themselves, where night and day last up to half of a year if there's any tilt.

Rassilon · Post #11by **Rassilon** » 20.05.2006, 19:10

Man I gotta start making addons again... This is spurring some ideas

rthorvald · Post #12by **rthorvald** » 20.05.2006, 19:21

Rassilon wrote:Man I gotta start making addons again

Yes, please do... We want our resident poet back!

- rthorvald

Rassilon · Post #13by **Rassilon** » 20.05.2006, 19:48

rthorvald wrote:
Rassilon wrote:Man I gotta start making addons again

Yes, please do... We want our resident poet back!

- rthorvald

Your poetry is harvested in the pictures you draw my friend!

Telepath · Post #14by **Telepath** » 21.05.2006, 06:01

I'm surprised the gravity works out right. How was this calculated.
It seems to me to be logical that the gravity on the inside of the hoop would be slightly less than on the outside of the hoop as the pull of the opposite sides of the hoop only 140,000km away would be significant and in the opposite direction ion the inside.

eburacum45 · Post #15by **eburacum45** » 21.05.2006, 08:18

I've given the model a tilt of 23 degrees; that should make the seasons fairly Earth-like. Actually the inner side of the Hoop gets a comparable amount of insolation to the outer at that angle so should be a similar temperature.
According to the simulation the Hoop is 'critically stable'; which means that a little bit of tidal braking would slow it down and tear it apart. This probably shows why they don't occur in nature.