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Life on an Anderson disk

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FrodoGoofballCoTV from Colorado, USA Since: Jan, 2001
#1: Feb 27th 2011 at 7:37:50 PM

Imagine Saturn's rings scaled up to the size of Earth' orbit and placed around the sun. Now imagine that rather than being composed of trillions of relatively small particles, it's a single, solid disk. Handwaving the structural and stability requirements for the moment, imagine that the density and thickness of the disk are such that the gravity field over most of the disk is perpendicular to the surface and high enough to form an atmosphere. Near the edges, the gravity shifts so it feels like you are going uphill, trapping the atmosphere.

Standing on the surface, the sun is always on the horizon, never moving. There are no days, no seasons. Halfway between the inner and outer edges, the average temperature is relatively pleasant. Approaching the inner rim, right before the gravity gets wierd, it becomes too hot to support most forms of life. Approaching the outer rim, it becomes too cold.

I was trying to figure out what the weather on such a world would be, what sort of creatures might live there.

I imagine that there might be a mountain range that would cast a shadow hundreds of miles long, creating a vast region where the sky is bright but the land is always dark.

MattII Since: Sep, 2009
#2: Feb 27th 2011 at 11:37:40 PM

Well we'd be living a lot closer to the sun for a start because it'd be too cold out near earth's orbital distance (think of the poles, the sun hits those at a much flatter angle than the equator, but a sharper angle than what an Anderson disk would get. Apart from that, you'd probably get a narrow band of proper vegetation, starting at ground-cover plants and working, by increasing height up to trees the size of sequoias. Lands further in than this band would be desert, with stubs of grasses and cacti, and further out would be tundra, cold desolate areas that would see just enough sun to maintain a sort of half-dead wilderness.

For the rest of it, like weather, I'm really not sure.

Yej (4 Score & 7 Years Ago) Relationship Status: They can't hide forever. We've got satellites.
#3: Feb 28th 2011 at 8:31:19 AM

Is the disk spinning, in any direction? That's incredibly important. Also, if it's not moving or spinning, what stops the atmosphere simply stopping, or becoming relatively static? (For instance, you might get a continuous, unchanging wind from the interior to the rim.)

FrodoGoofballCoTV from Colorado, USA Since: Jan, 2001
#4: Feb 28th 2011 at 8:40:43 AM

[up]My thinking was, it is rotating at a rate somewhere betwwen the natural orbital velocity at the inner and outer edges.

just bugs meUnlike the Earth, the disk's mass may not be small compared to the star, so I'd have to take that into account.

edited 2nd Apr '11 8:03:46 AM by FrodoGoofballCoTV

RalphCrown Short Hair from Next Door to Nowhere Since: Oct, 2010
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#5: Feb 28th 2011 at 10:06:20 AM

Assuming the disk is in the ecliptic and has an effective thickness of zero, we can deduce a couple of things. For one, any given portion on the disk itself would get only a fraction of the sunlight that an equivalent spot on a planet would get. On a planet, the surface faces the sun and gets a significant portion of light (the math is left as an exercise for the reader). On a disk, you lose more than half the light before you even begin to calculate the falling off due to distance and extreme angle, and anything that protrudes from the surface cuts off light for an astronomical distance behind it.

For another thing, the atmosphere on the sunward side would heat up, rise, and be replaced by cool air that cycles in from the outer side. There would be a constant cold wind from outer rim to inner. Not only that, the cold air would not carry much moisture. Rain forms when moist warm air meets cool dry air. When the lower, cooler, drier air reached the inner rim, it would turn into higher, warmer air, but it would still be dry. No rain to speak of.

So the first solution that comes to mind is to build large mirrors, possibly even a reflective half torus, around the outer rim and reflect sunlight onto the surface. Somebody's worked this out already, I'm sure, but this is the first time I've heard of an Anderson disk.

Under World. It rocks!
FrodoGoofballCoTV from Colorado, USA Since: Jan, 2001
#6: Feb 28th 2011 at 12:36:00 PM

[up] I would imagine the inhabitable climate closest to the sun would be a painfully hot high desert. So no moisture there. That would suggest the whole disk would be dry... tongue

idea UNLESS the movement of warm air to the cool regions was broken into bands as on Earth as diagramed here. You'd need more bands than the Earth has to get decent rainfall, because even assuming a disk substantially smaller than Earth's orbit the distance between inner and outer rim would probably still be over a million km.

The bands occur because the surface of the Earth absorbs and retains heat better than the air, so you get pockets of warm air near the surface in temperate regions that want to rise to replace the tropical warm air which has cooled off during the hours or days it took to get to the temperate regions. But with the sun on the horizon 24/7, would the land be able to produce those pockets of warm air? Possibly on the sides of hills facing the sun, or in the subtropic climate regions where the sun is much brighter than on Earth.

[awesome] However, I like the idea of having some sort of mirror system to increase the illumination on the surface. Then you would definately get more surface heating and more Earthlike weather. It would also increase the useful habitable area. You could even create variations in sunlight over time, creating a day / night / season cycle.

Yej (4 Score & 7 Years Ago) Relationship Status: They can't hide forever. We've got satellites.
#7: Feb 28th 2011 at 1:16:45 PM

[up] Wouldn't variations involve moving the mirrors?

MattII Since: Sep, 2009
#8: Feb 28th 2011 at 1:40:44 PM

Oh, and I just checked up, and it's actually called an Alderson Disk, not an Anderson disk.

edited 28th Feb '11 1:41:14 PM by MattII

FrodoGoofballCoTV from Colorado, USA Since: Jan, 2001
#9: Feb 28th 2011 at 2:30:06 PM

[up]So it is!

[up][up]Yes, but it might not require more movement than the rotation of the disk. If the disk and the mirrors were "orbiting" at different rates, the mirrors would move relative to any given spot on the surface, rather like the shadow squares in Larry Niven's Ringworld.

edited 28th Feb '11 2:30:15 PM by FrodoGoofballCoTV

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