Detecting a Banks orbital from Earth

[Modax]

Suppose, in an alternate universe, the Culture had colonized our solar system thousands of years ago, disassembling mars to build an orbital in mars current orbit. It would have a diameter of 1.4 million km (same diameter as the sun) a cross section of 1500 km, and mars mass. My question is, would it be visible to the naked eye from earth? Lets assume that the back surface of the structure has a reflectivity like polished metal. Since its cross section is smaller than the diameter of pluto, that would make it hard to see, right?

With the invention of sensitive telescopes, I assume that astronomers would soon discover such a reflective object. But what would they make of it? If we assume that the Culture built the orbital so that its cross section faces the Earth head on, it would just look like an extremely long, thin line. Would scientists have been able to discover its true nature before the space age and the sending of space probes?

P.S I just thought it would be an interesting hypothetical situation; I don't actually think that the Culture exists!

[NecronLord]

They're inclined towards the sun, to allow part of the inner band to have daylight. As such, it'd look like a compressed O. It would have some confusion about its nature (the 'theory' that the ring of saturn was the foreskin of Christ springs to mind) until what it was could be seen in more detail, though.

[XaLEv]

Why would they build an Orbital that size with over 150 times the mass necessary?

[Modax]

Are they really that light mass-wise? I can't seem to find where it says the mass of an orbital in any of the books, but wikipedia says they have "a surface area of between 20 and 120 times that of the Earth (but comprising roughly the same amount of mass)." I guess wikipedia isn't to be trusted on these matters.

[Junghalli]

They're inclined towards the sun, to allow part of the inner band to have daylight. As such, it'd look like a compressed O.

With somewhere between half and twice the apparent diameter of the sun, depending on where it is in its orbit relative to Earth, I'd imagine. I wonder what effect that would have on early cosmology.

I'm guessing assuming it was naked-eye visible we'd see something like this:



That's a pretty interesting idea actually: a primitive race developing on a planet with such a construct visible in its night sky.

[XaLEv]

Are they really that light mass-wise? I can't seem to find where it says the mass of an orbital in any of the books, but wikipedia says they have "a surface area of between 20 and 120 times that of the Earth (but comprising roughly the same amount of mass)." I guess wikipedia isn't to be trusted on these matters.

http://www.cs.bris.ac.uk/~stefan/culture.html

The attraction of Orbitals is their matter efficiency. For one planet the size of Earth (population 6 billion at the moment; mass 6x1024 kg), it would be possible, using the same amount of matter, to build 1,500 full orbitals, each one boasting a surface area twenty times that of Earth and eventually holding a maximum population of perhaps 50 billion people (the Culture would regard Earth at present as over-crowded by a factor of about two, though it would consider the land-to-water ratio about right). Not, of course, that the Culture would do anything as delinquent as actually deconstructing a planet to make Orbitals; simply removing the sort of wandering debris (for example comets and asteroids) which the average solar system comes equipped with and which would threaten such an artificial world's integrity through collision almost always in itself provides sufficient material for the construction of at least one full Orbital (a trade-off whose conservatory elegance is almost blissfully appealing to the average Mind), while interstellar matter in the form of dust clouds, brown dwarfs and the like provides more distant mining sites from which the amount of mass required for several complete Orbitals may be removed with negligible effect.

[Modax]

That's a pretty interesting idea actually: a primitive race developing on a planet with such a construct visible in its night sky.

Awesome! I'm flattered that you made this drawing just for my humble thread on such short notice

Maybe this could spawn a culture fan-fic of some kind. I'm not much of a writer though. I'm more of the worldbuilder type.

[Junghalli]

Awesome! I'm flattered that you made this drawing just for my humble thread on such short notice

A minute of playing around with Paint, it was nothing.

[Modax]

Well, if the mass of Earth could build 1500 orbitals, then

6e+24 kg / 1500 = 4e+21 kg for the orbital's mass

while the mass of the asteroid belt is 2.829e21, or just over 70% of the required mass.

The orbital specifications I gave in my first post are significantly smaller than a standard orbital, so there should probably be just enough for that design in the asteroid belt.

So if we put the orbital safely outside the orbit of mars -- lets say halfway between mars and jupiter -- how much does that reduce the angular diameter?

This way, the culture is also providing an enormous service to earth dwellers by clearing out the asteroid belt. I read that Ceres has more fresh water than there is on earth, so that would provide the orbital with an ocean right there. A fresh-water ocean at that!

[Junghalli]

So if we put the orbital safely outside the orbit of mars -- lets say halfway between mars and jupiter -- how much does that reduce the angular diameter?

The problem with an orbit that far out is that it probably places the orbital outside the life zone. It might be a better idea to place it between Mars and Earth, or at the L4 or L5 point of either Mars or Earth.

Between Mars and Earth it would look bigger. At the Martian L4 or L5 points it would look the same as if it was in the place of Mars. IIRC at the Earth L4 or L5 point it would always be 1 AU from Earth and so it would have the same apparent diameter as the sun at all times (as opposed to other scenarios where the apparent diameter would vary significantly depending on where in its orbit it was relative to Earth). At the Earth L4 or L5 point I imagine it might only be observable a little after sunset or before sunrise, like Venus and Mercury, just looking at the angles involved (here's a pic).

I'm not sure which of these orbits would be most stable, or if any of them would be indefinitely stable. Though I'd point out a civilization capable of building such a construct should also be capable of building some humongous solar panels to give it active stationkeeping. And I imagine a civilization like the Culture, not restrained by presently known physics, could probably come up with a much less clunky solution.

[Modax]

If they had to put it outside of mars' orbit I suppose they could put Sulfur Hexaflouride in the atmosphere, which is odorless, colourless, nontoxic, and a greenhouse gas 22 000 times more potent than CO2 by mass. That would make it warm, but would there be enough sunlight for photosynthesis at that distance?

[Modax]

Amazing. The scale of the solar system never ceases to amaze me. The closest approach ever between Earth and mars was 55.8 million kilometers, which would (should) leave lots of room for a 1.4 million km diameter orbital, 10 times the diameter of Jupiter. If the orbital was halfway between earth and mars during such a close approach, the distance from Earth to the orbital is still 71 times the distance from earth to the moon.


the cross section of the orbital is about 40% of the diameter of the moon, and 71 times farther away when its nearest. that would give it 0.6% of the moon's apparent diameter, if i did the math right. I wish I had Celestia working on this computer, and knew how to mod for it.

[Modax]

the cross section of the orbital is about 40% of the diameter of the moon, and 71 times farther away when its nearest. that would give it 0.6% of the moon's apparent diameter, if i did the math right. I wish I had Celestia working on this computer, and knew how to mod for it.

so the moon is about 1800 arc seconds, so 0.6% of that is 10.8" or about the angular diameter of Venus. Needless to say, that would make it a very bright ring in the sky, if all my calculations so far are correct.

[Modax]

Some worldbuilding ideas and timeline for alternate universe based on the above scenario

The 1.4 million km orbital was constructed c. 3000 B.C.E, and orbits halfway between Earth and Mars. With a minimum distance of 22.7 million kilometers and a maximum distance of 50 million km. It is a prominent feature of Earth's night sky, and clearly visible to the naked eye most of the time.

The Sol Orbital is somewhat smaller than average for a culture orbital, with a 25 hour day, and a comfortable surface gravity of 0.4g. Atmospheric pressure is only 50 kPa, which allows for faster and easier travel due to decreased drag. Compensating for this, the oxygen concentration is double that of Earth. 59% nitrogen, 40% oxygen, 0.9% water vapour, 0.1% carbon dioxide. This very high concentration of CO2 gives a powerful greenhouse effect that gives the orbital an average surface temperature of 23 degrees Celsius. The whole orbital has a sub-tropical terrestrial climate, with millions of kilometers of fine white sand beaches, and a fresh water ocean covering 60% of the surface.

the other side of the ring houses enormous observation equipment, such as a 500 km parabolic radio telescope dish, and a series of 25km diameter optical telescopes, capable of observing the surface of Earth in great deal, these facilities are safe, because fleets of ships have thoroughly cleared the system of interplanetary debris in the construction of the orbital.

The Sol orbital features a strong role in the creation myths of almost all human societies. In many mythologies, it is a deity alongside the Moon and Sun.

timeline

c. 3000 B.C.E ring is constructed over a 10 year period. Ancient Egyptian astronomers witness the appearance of the ring, and record this event in various hieroglyphs.


1400 C.E Contact agents introduce weakened strains of European microbes to Amerindian peoples,( c. 1400 c.e) allowing them to better resist conquest, and avoid cultural extinction. As a result, the Aztec and Incan empires survive as independent political entities up into the 1850's when industrialized Europeans finally overwhelm them.

1609 C.E Galileo uses his x30 telescope to discover that the inner surface of the ring has blue and green regions, which he hypothesizes to correspond to oceans and forests.

19th century C.E industrial age giant refracting telescopes establish that sol orbital has lakes, rivers, islands, and mountains. Because the night side of the orbital is never visible from Earth, artificial light from the orbital's cities is never seen.

1890's spectroscopic analysis of the orbital's atmosphere adds to mounting evidence that the orbital is populated. World religions have to come to terms with a 'second creation' that is not mentioned in holy texts. (how come the prophets didn't know the orbital was populated?)

1937 the first radio telescopes detect Culture radio emissions originating from the Orbital. An Arecibo-style message is sent to orbital and first contact is established.

1940's Contact agents infiltrate Nazi Germany and prevent the Holocaust. Stalin is similarily assassinated and the cold war is averted.

1950's An age of Culture-Terran mentorship (similar to the mentorship shown in Matter) begins


Let me know what you guys think.

[Modax]

Edit: on second thought, it makes more sense for Contact to aid the Incans, but not the aztecs, for while the Aztecs practiced massive human sacrifice, the Incans were fairly benevolent as empires go and didn't massacre people.

[NecronLord]

It's worth noting that canonically, 1970s Earth isn't so bad, by Culture standards. They come, they see, they leave the planet alone to use as a control in experiments on other, similar worlds. They certainly didn't feel compelled to intervene.

[LadyTevar]

It's worth noting that canonically, 1970s Earth isn't so bad, by Culture standards. They come, they see, they leave the planet alone to use as a control in experiments on other, similar worlds. They certainly didn't feel compelled to intervene.

But they did steal the idea of Light Sabers.

[andrewgpaul]

I'm not sure they actually thought it was a good society; just that it would make a good control.

In any case, they changed their minds (and possibly Minds) after 200 years or so.

[Marcus Aurelius]

I'm not sure they actually thought it was a good society; just that it would make a good control.

Actually they thought that Earth was pretty bad for a relatively advanced industrial society with humanoid inhabitants. On comparison the last major wars in the Culture "mother" worlds were fought with Napoleonic technology. My interpretation was that they needed a "negative" control (i.e. no SC involvement) for a severely screwed humanoid inhabitated planet.

[Ariphaos]

Edit: on second thought, it makes more sense for Contact to aid the Incans, but not the aztecs, for while the Aztecs practiced massive human sacrifice, the Incans were fairly benevolent as empires go and didn't massacre people.

...Incans, benevolent? Runatinyas are made of sunshine?

[NecronLord]

I'm not sure they actually thought it was a good society; just that it would make a good control.

Actually they thought that Earth was pretty bad for a relatively advanced industrial society with humanoid inhabitants.

Which just makes them particularly peaceful, or uplifted by another civilization. Given that we regularly see other humanoid worlds in the same setting with more advanced technology having wars. The ordinary people involved thought it was pretty bad, because they were confronted with the horrors of a primative world directly. The minds seemed a lot more sanguine about the place.

On comparison the last major wars in the Culture "mother" worlds were fought with Napoleonic technology. My interpretation was that they needed a "negative" control (i.e. no SC involvement) for a severely screwed humanoid inhabitated planet.

Eh. Earth manages to join the Culture (an act itself supposedly the exception to the rule) eventually. It can't be 'that' screwed.

[andrewgpaul]

What are you basing that (Earth becoming a member) on? Not that I'm saying you're wrong, it's just not something I've picked up on.

[NecronLord]

What are you basing that (Earth becoming a member) on? Not that I'm saying you're wrong, it's just not something I've picked up on.

I honestly don't recall. I believe it's an afterword of State of the Art or some such. Unfortunately, I do not own a copy of that anthology, although I have read it.

[The Nomad]

It's mentionned in the appendices of Consider Phlebas (which are in themselves part of a history manual released by Contact for the benefit of Earthlings).

[andrewgpaul]

Thought that's what he was referring to. I always read that as something produced to bring Earth 'up to speed', not necessarily joining the Culture as such.