Increadibly large artifical planet

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Let us construct an artificial planet out of unobtainium between ~ Mars and Venus in a circular orbit radius = one AU. On another board www.abuzz.com the concensus is the inner planets will collide long term, so we will make them moons of the incredibly large planet. Sorry about the changes~ The radius is one million KM, so it is bigger than the sun, but about the mass of Neptune as it is hollow. Would it produce a total eclipse of the sun occasionally ~as viewed from Jupiter' moons. I don't see why not~ What would the surface gravity be? Some claim a hollow (thin wall) sphere produces no gravity anywhere inside. ~I don't believe that. I would guess the gravity on the inner surface is about 1/2 the gravity on the outer surface~ You may assume a sphere wall thickness of unobtainium that is compatable with the properties of common glass, except a billion times stronger than glass. Will that give a generous safety factor if pressurized with 98% oxygen at 3 psi = pounds per square inch, less in some parts of the interior? Would the mass of the atmosphere inside exceed the mass of the unobtainium shell? If so the atmosphere would shift the pressure and gravity gradients inside the sphere radically? What is the maximum air temperature inside the sphere? Neil

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Why?

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Real estate... solar power...

On the other hand, why not just build a Dyson sphere?

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I still can't figure out how the planet can be hollow.

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So then ya buld the thing then what?

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Most planets cannot be hollow. The key here is the material Niel's planet is made of ... unobtainium. Start with that material and you can make any planet you want, irregardless of the laws of physics.

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and it's a fictional material, yes? Sorta like the ringworld?

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Heck Neil, I wouldn't worry about getting "unobtainium". Just use sand and pay a little attention to Mr Einstein and you should be able to build a stable structure anywhere you want.

Any shape you want so long as it's round, more or less. Don't expect it to just sit there though Very Happy

Location may be another problem. Building it amongst the Oort cloud would probably minimize the materials necessary, but the value of real estate in that neighborhood may prohibit the cost effectiveness of the project. Location is everything in the real estate business. Rolling Eyes

For a million dollars ( I will give you a "quit claim deed" to a million cubic miles of the Oort cloud neighborhood. Heck, I would probably settle for ten bucks if you really want it. Exclamation

I'm so generous I am always broke Exclamation

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Mechsmith, that sounds like the deal of the millennium. For another ten buck, I'll vacate any claims I have to any passing comets that might be useful for this enterprise.

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Acquiunk,

Actually some planets, especially this one may be described as hollow, albiet with very thick walls. Confused

Since gravitys effect is decreased with the depth of the hole I suspect that , with no effective gravity to hold the liquid metals forming the core in the middle and a small centrifugal effect at any other place I suspect that this planet is hollow if you stretch the meaning of the word to its limits. The size of the cavity though, I wouldn't care to guess Exclamation

The real estate deal is just to good to pass up. Much better than the one involving a bridge across the East River in NYC, USA. Laughing

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For the world is hollw and I have touched the sky...

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Hi aka: I think someone answered most of the other questions, except the questions I asked. My guess is to produce the cavity at the center of the Earth, you suggested, the present earth would need a thick coat of unobtainium to allow it to spin fast enough. A two minute day perhaps? That is because the weight of most the matter above the cavity would have to be neutralized by the spin.
I decided we should spin the equator of the incredibly large planet at 6 MPH = 10 KMPH. Since the length of the equator is 6,280,000 KM that makes the day 628,000 hours long. This would ensure little effect on the gravity but would effect the maximum air temperature. Sorry this is getting complicated.

Why? Sometimes we consider what can be done with the right materials and we discover it has an important use after we figure out the details ie in this case a few trillion humans could possibly live on the inner surface of the sphere. Neil

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why not just build a Dyson sphere? ~That is a much larger sphere with the sun in the center. Three billion times the strength of glass is likely strong enough after the sphere is complete; but part of a sphere is much weaker, so how do you build a Dyson sphere one little peice at a time? How hot would the inside surface of a Dyson sphere get, same unobtainium, ten KM thick, if the radius is one AU. What would be the new color temperature of the sun's photo sphere considering the energy radiated by the hot surface of the Dyson sphere and the energy reflected back toward the sun? I suspect we need to think at least 3 AU radius to avoid vaporizing Mercury and Venus. Neil~

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i suspect Neil, that you might have to do a very comprehensive 'environmental impact analysis' (at least here in Canada, i'm sure "W" would accept 'cash up front', since he can't read) before you would get the building permit.

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We can sorta check my gestimate that the unobtainium is 10 KM thick. The volumn of a sphere is 4/3 pie r cubed = 4.19 times 10^18 cubic KM then calculate the volumn for 10 km more radius. 1000030000300001000 is the radius cubed? Multiplied by 4.19 then subtract to get the volume of Neptune in cubic KM assuming glass has the same density (average) as Neptune. A 19 digit calculator would be helpful. I'm confused plus I think Neptune's average density is a bit less than that of common glass. Neil

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Neil,
Now maybe I can really Help.

If you are running a Windows 95 or 98 there is a Calculator hidden in your Help Menu.

Open Help----> Index----> Calculator-----> Display

You will find enough numbers there to be able to calculate anything that will fit in the Solar System, and a good bit beyond.

There is a Scientific and a Standard availiable.

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as a 'historic' note; Mars has two moons, Demos and Phobos.
Phobos was named thus since it appeared much brighter than its size would suggest, when viewed through a telescope many years ago when it was discovered. A theory arose that it was possibly an artificial satelite of Mars, built by Marsians, and placed in orbit around the red planet. This has however been debunked by recent probe photos, showing a rather ordinary, if highly reflective lump of rock.

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I got confused when neil interpreted "artificial planet" to mean a sphere encasing the earth. Or was that some other thread?

Anyway, there are no theoretical problems with having a hollow artificial planet (except obtaining the building resources, of course!). However, I would think that it should be rotating. This would, by centripetal force, 'push' all the objects inside toward the inner surface of the spere, creating an 'artificial gravity'. Of course, by controlling the speed of rotation (and your angle from the axis of rotation) you could control the force of gravity - it would be highest along the axis, and non-existant at the two radial areas.

Perhaps there is a way to spin the sphere and create a constant outward force on all points of the inner surface? Somehow have the sphere rotating on more than one axis, perhaps? I just like gravity, I must be used to it. Makes it easier to walk around and stuff. However, if you had the equivalent of moon gravity, ~g/6... that would be c00l!!

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you need to read Arthur Clarke's 'Rama' series; all about an artificial world lost floating in space.

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Increadibly large artifical planet

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