Artificial Moon?

Lythande · Nov 10, 2014

Say you have an advanced human people who wanted to terraform a planet to their liking; if the planet was a little too far from the star, or just had an unfortunate climate, would it ever actually make sense for them to have created some sort of giant sun reflector that, from the planet's surface, would look like a large moon that had no phases?

I assume that reflecting a large amount of sunlight back at the planet like that would warm it up and change the climate, possibly calming out some of the variances in weather since it would be getting more energy at night. These people also use solar-powered nanites so I figured that would be good for them.

I'm not actually writing hard scifi (this would all be background flavor, really) so I don't need to actually have a firm grip on the science, and it seems rational to me, but I want to make sure it's not something that would make more knowledgeable people roll their eyes.

Edit: I realize I gave the wrong impression. I'm actually writing fantasy with deep-in-the-background scifi tech and am checking plausibility of my moon's backstory, not looking for ways to terraform, ince this terraforming happened thousands of years ago. Sorry about that.

King Neptune · Nov 10, 2014

The energy required to build such a thing would be huge. There would have to be some compelling reason for building such a thing, instead of going to another star. Think of a good excuse for doing it, and it could be accepted. The required technology isn't all that advanced, but just moving the rock around would be a lot of work.

Albedo · Nov 10, 2014

The Earth receives basically no warmth even from a full moon - it'd need to be much brighter than that to be any use. Is it a big parabolic reflector with the planet at its focus? Then it would be huge in the sky, but comparatively dim.

benbradley · Nov 10, 2014

Lythande said:
Say you have an advanced human people who wanted to terraform a planet to their liking; if the planet was a little too far from the star, or just had an unfortunate climate, would it ever actually make sense for them to have created some sort of giant sun reflector that, from the planet's surface, would look like a large moon that had no phases?

Such large structures in space don't need to be very strong unless it needs to be moved fast under acceleration, and this one wouldn't. A structure like this may take months to both build and to put into place, as they're (mostly) in zero g. There WILL be some structural strength needed partly because one part of it is a few miles closer to the planet and/or the star than the other (the parts are in slightly different orbits, and holding them the same distance apart causes some force to be exerted in the structure). The actual reflecting surface would be a metal film or metal-coated mylar that is very thin and thus has very little weight. It will last a long time because theres very little in space to hit it to tear it or make holes in it.

I assume that reflecting a large amount of sunlight back at the planet like that would warm it up and change the climate, possibly calming out some of the variances in weather since it would be getting more energy at night.

Yes it would warm it up, but everything I hear about Global Warming/Global Climate Change says that an atmosphere with a higher temperature has more energy, and causes more storms and makes the storms more intense. If the moon's atmosphere is relatively cold, it may not have storms at all.

As a real, known (and uncontroversial) example, a hurricane over a warm area of ocean builds up strength faster and gets to a higher strength than one over a cooler ocean area.

These people also use solar-powered nanites so I figured that would be good for them.

I'm not actually writing hard scifi (this would all be background flavor, really) so I don't need to actually have a firm grip on the science, and it seems rational to me, but I want to make sure it's not something that would make more knowledgeable people roll their eyes.

If you want the last part I bolded (and I think this is a Good Thing, as I'm a hard SF fan and I think the dissemination of science and the knowledge it produces is a Good Thing even, perhaps especially when done in fiction), you pretty much ARE writing hard SF.

Lythande · Nov 10, 2014

King Neptune said:
The energy required to build such a thing would be huge. There would have to be some compelling reason for building such a thing, instead of going to another star. Think of a good excuse for doing it, and it could be accepted.

Well, there is a compelling reason, for these people; they're weirdo mystical-science types with some odd obsession with the number 8 (the planet has .8g, the year is divided into 8 months of 8 weeks of 8 days, hours have 64 minutes which have 64 seconds, and they use a base-8 number system), and I'm sure that can be worked into them choosing this planet (along the same vein as how indigo was added to the color spectrum to get to 7 colors). It's not a logical reason, but compelling for them.

Albedo said:
The Earth receives basically no warmth even from a full moon - it'd need to be much brighter than that to be any use. Is it a big parabolic reflector with the planet at its focus? Then it would be huge in the sky, but comparatively dim.

Hm. Yes, a parabolic reflector I suppose is what I was thinking of, though I was also picturing some much larger and brighter than our moon, mostly because it's much closer (the natural moon gets eclipsed behind it regularly). I suppose I'm wondering why it would be dim if it's gathering up sunlight to reflect.

benbradley said:
[...] The actual reflecting surface would be a metal film or metal-coated mylar that is very thin and thus has very little weight. It will last a long time because there's very little in space to hit it to tear it or make holes in it.

This is actually perfect A) because it's been there for at least a thousand years with only automated repairs, and B) that's actually more what I was picturing; some sort of mirror that looks like a moon from the planet, since I'm not sure why they would bother constructing a full sphere when they only needed one surface or actually moving a moon in. Although, with their mystical weirdness above, it's not inconceivable.

benbradley said:
Yes it would warm it up, but everything I hear about Global Warming/Global Climate Change says that an atmosphere with a higher temperature has more energy, and causes more storms and makes the storms more intense. If the moon's atmosphere is relatively cold, it may not have storms at all.

As a real, known (and uncontroversial) example, a hurricane over a warm area of ocean builds up strength faster and gets to a higher strength than one over a cooler ocean area.

Hrm. Good points. Maybe the planet's climate was cold and stagnant and reflecting energy back in was to give it life, instead of being silly and trying to even it out by supplementing lost energy.

benbradley said:
If you want the last part I bolded (and I think this is a Good Thing, as I'm a hard SF fan and I think the dissemination of science and the knowledge it produces is a Good Thing even, perhaps especially when done in fiction), you pretty much ARE writing hard SF.

Okay, then I'm writing hard SF under a mile-thick layer of Fantasy

Magic is caused by nanites and as far as the people are concerned, they have a big white moon with no phases. I'm not actually planning on ever explaining the SF or technology outright, even as obviously in the Sword of Shannara; I just want to know what's going on in the background for myself so that if someone does realize it (or eventually I do make it more obvious) they could go back and have it all click, without seeing handwaves all over.

Drachen Jager · Nov 10, 2014

We're doing a great job warming up our own planet with CO2 emissions. Don't need no giant reflector, just change the composition of the atmosphere.

King Neptune · Nov 10, 2014

Two sets of eight reflectors each circling the polar regions, so the reflectors would be out of the plane of the planet's orbit. The reflectors would have fixed foci and a simple orbit, and they couldn't be aimed much, but they would turn as the planet did and reflect light onto the planet. how much heat would be involved would depend on the size and the efficiency os the reflectors. They would be big Mylar parabolas. How big would depend on what they could afford.

Drachen Jager · Nov 10, 2014

King Neptune said:
Two sets of eight reflectors each circling the polar regions, so the reflectors would be out of the plane of the planet's orbit.

That's not possible.

You cannot orbit the pole of a planet, gravitational forces dictate you must go the long way 'round.

You could go from one pole to the other, but that's an entirely different story, and not what you seem to have in mind.

King Neptune · Nov 10, 2014

Drachen Jager said:
That's not possible.

You cannot orbit the pole of a planet, gravitational forces dictate you must go the long way 'round.

You could go from one pole to the other, but that's an entirely different story, and not what you seem to have in mind.

I believe that you are mistaken. The orbit would require some energy input, but a geosynchronous orbit could be done. It might turn out that the orbits would require a sinuous track that would go as far as the upper latitudes.

Drachen Jager · Nov 10, 2014

If it requires constant energy input, it's not an orbit.

I think you'll find "some" energy input for the holding pattern you're describing would turn out to be quite a massive amount, unless the satellite was very distant (which would sort of defeat the purpose).

Dennis E. Taylor · Nov 10, 2014

What about just using a massive injection of greenhouse gases? "Massive" doesn't have to be enough to affect the breathability of the atmosphere, either. Another option, if the planet has a high albedo (planetwide ice sheets?) would be to sprinkle liberally with fine carbon particles to increase heat absorption.

Lythande · Nov 10, 2014

We're actually going the wrong direction with this XD I'm not actually looking for a way to warm up or climate-control the terraformed planet, I was considering a neat explanation for a moon they already have. They could just have a big ol' phaseless white moon, but I thought the sun reflector was a good subtle technological explanation and I wanted to check plausibility.

Dennis E. Taylor · Nov 10, 2014

Lythande said:
We're actually going the wrong direction with this XD I'm not actually looking for a way to warm up or climate-control the terraformed planet, I was considering a neat explanation for a moon they already have. They could just have a big ol' phaseless white moon, but I thought the sun reflector was a good subtle technological explanation and I wanted to check plausibility.

Does the moon already have an atmosphere? It being a moon actually helps, because you can put the reflectors in the leading and trailing Trojan points. You'd have to clear them first (they tend to accumulate space junk), and you give the reflectors a slow rotation so that they're always aimed at the moon.

If there's no atmosphere, this is pointless though.

Edit: sorry, just re-read your post, and I think I'm still missing the point.

Muppster · Nov 11, 2014

Phaseless makes me scratch my head a bit: the phases come from the moon being in orbit of the planet... to be constantly a full moon it would have to be fixed in space while the planet turned under it (not a geosynchronus orbit; that orbits at the rotational speed of the planet, so appears to hang in the sky above a single point on the ground) and yet orbit the sun with the planet. (Remember: we see the same face of the moon all the time because it rotates on its axis as it orbits us, the phases are not about it turning but where it is relative to us/the sun)

I guess you could light up the satellite so it's a pretend full moon (ie not reflecting sunlight, emitting light 24/7), but I don't know why it would feel credibly necessary.

Re obsession with 8... just a thought: there's a reason vast tracts of human history has been using 12 and 60 as divisions of time and other things (distance, money, etc): because they're conveniently divisible numbers with lots of useful factors. Also given the difficulty humans have had moving away from the Babylonian base-60 timeframe, I find it a little difficult to believe a bunch of folks would plop down on a new world and adapt everything to a new base-8 frame of reference. Sure, time might have to be divided logically by the length of day, but we count base-10, -12, and -2 as it suits (decimal, pre-decimal measures, binary) and measure time base-60. I'm also considerably more skeptical of a planet with such regular and rounded orbital parameters: we have leap-years and leap seconds because the Earth isn't turning at a constant rate (slowing down...very very slowly), and orbits at 365-and-a-bit days. If this artificial world is created so perfectly...why the need for the moon to tweak things to be more habitable? Just make it perfect in all respects.

King Neptune · Nov 11, 2014

Drachen Jager said:
If it requires constant energy input, it's not an orbit.

I think you'll find "some" energy input for the holding pattern you're describing would turn out to be quite a massive amount, unless the satellite was very distant (which would sort of defeat the purpose).

Actually, the energy input would be part of the function. It would be a solar sail, and the trouble would be keeping it on station. Balancing the solar pressure and the gravity should be possible; it would depend on size and the star's output and the planet's gravity .8g. Regardless of the orbit, balancing the light pressure would be necessay, and putting the mirrors off the poles would keep them from interfering with normal sunlight.

Albedo · Nov 11, 2014

Lythande said:
Hm. Yes, a parabolic reflector I suppose is what I was thinking of, though I was also picturing some much larger and brighter than our moon, mostly because it's much closer (the natural moon gets eclipsed behind it regularly). I suppose I'm wondering why it would be dim if it's gathering up sunlight to reflect.

Think of the apparent size. Our moon is very far away. a parabolic reflector would be closer and hence much larger in the sky. But because it would cover a much larger part of the sky than our sun (same size as the moon, remember), if it was delivering a similar amount of light, it would have to be dimmer. If each part was as bright as the sun, we'd be fried like ants under a magnifying glass.

Muppster said:
Phaseless makes me scratch my head a bit: the phases come from the moon being in orbit of the planet... to be constantly a full moon it would have to be fixed in space while the planet turned under it (not a geosynchronus orbit; that orbits at the rotational speed of the planet, so appears to hang in the sky above a single point on the ground) and yet orbit the sun with the planet. (Remember: we see the same face of the moon all the time because it rotates on its axis as it orbits us, the phases are not about it turning but where it is relative to us/the sun)

Couldn't you sit it at the L2 point in the primary-planet system? Assuming it was a very light reflector it wouldn't significantly unbalance the planet's orbit and could sit there for a long time with only minor corrections, always at the point directly opposite the sun and hence in full phase.

Maxx B · Nov 11, 2014

How about thousands of smaller reflectors orbiting the planet? They could be run like a power utility. The affluent in society have all the heat they need and the poorer folk who can't afford the utility have to suffer. A large number of the reflectors would provide the heat across the planet, and if needed you have an extra story mechanic that could drive the conflict between the haves and have nots.

Casey Karp · Nov 11, 2014

We're still going in the wrong direction here. The OP is NOT asking for a way to terraform the planet. He wants the visual effect of an eternally-full moon and is asking for a justification of that effect.

Lythande, I don't have the math to comment authoritatively about the practicality of your reflector idea, but I get the impression from the conversation that it would be possible to get the effect you want, but it probably wouldn't do much to improve the climate.

That said, there is something in your background that rather bothers me. Finding a habitable or near-habitable planet that just happens to have exactly the right mass, rotation, and orbit to give you your nice, neat multiples of eight is slightly less probable than my chances of finding a lost lottery ticket with the winning numbers for the next $100,000,000 jackpot. Sure, you're the author, and you can assert that they lucked out--but if you do, you've more than used up your one permitted major coincidence for the story. ;-)

You might be better off hinting that their technology was good enough to allow them to move the planet where they wanted it and tweak its rotation. As an added bonus, if you do that, you might as well say they put a moon in the right orbit because they liked long, moonlit nights.

Artificial Moon?

Lythande

I, am that is.

King Neptune

Albedo

Alex

benbradley

It's a doggy dog world

Lythande

I, am that is.

Drachen Jager

Professor of applied misanthropy

King Neptune

Drachen Jager

Professor of applied misanthropy

King Neptune

Drachen Jager

Professor of applied misanthropy

Dennis E. Taylor

Get it off! It burns!

Lythande

I, am that is.

Dennis E. Taylor

Get it off! It burns!

Muppster

King Neptune

Albedo

Alex

Maxx B

Casey Karp