Gliese 581-G (Just for fun)

[Meshon]

I forgot about gravity.

So many times I've wanted to do that.

[Azélor]

I'm not sure that your planet can have a satellite because it is tide locked. Think about it, the gravity pull form the star is strong enough to stop the rotation of the planet. What would happen to the satellite in that case?

[Raptori]

Thinking about it you're right. The moon would have to be far closer to the planet for it to orbit the planet rather than the sun, so a smaller moon moving at extremely high speed and relatively low altitude orbit would be more plausible... o.O

[JefBT]

Also, orbiting at high speed on low altitude may impact the planet's rotation as well, after some time. Or at least the water level may change very often.

[Azélor]

Thinking about it you're right. The moon would have to be far closer to the planet for it to orbit the planet rather than the sun, so a smaller moon moving at extremely high speed and relatively low altitude orbit would be more plausible... o.O

I don't think so but Universal sandbox indicate otherwise...

[acrosome]

Yes, a moon would be unlikely. Unless it were a recently captured vagrant.

With a giant ball of fusing gas in a predictable location in the sky, I doubt that the locals would care much about magnetic compasses. It would be pretty damned easy to fix your latitude, just by measuring the height of the sun above the horizon. As always, fixing longitude would be more of a challenge. In fact, my mind boggles on a way to do so, even with accurate clocks. Perhaps with very accurate stellar measurements, but that could only work near the ice zone where you can see the stars. The stars also wouldn't wheel around the pole star (if there is one) as quickly as they do on Earth- instead, one rotation would take one year.

More intersting is how they would define direction. North/South/East/West makes little sense. Perhaps they'd use a polar system instead? Clockwise, Widdershins, Axial, and Radial? (With Axial defined as "towards the spot where the sun is directly over head," and Radial as the opposite.)

Also, there's really no reason to expect the hot side to be all land, is there? There'd be no ice given the model you're using, true. But there might be a sea crossing the hotside pole. Land might run right up to the ice sheet in some spots. Etc. Because, yes, the planet would be pulled into a bit of an egg shape, but that tidal force is acting on the water too, so you can model it as a flat surface. High points are high, low points are low (and full of water, which is rapidly evaporating at the hotside pole).

[Podcreature]

I'm not sure that your planet can have a satellite because it is tide locked. Think about it, the gravity pull form the star is strong enough to stop the rotation of the planet. What would happen to the satellite in that case?

Really great feedback guys, thanks for sharing all your thoughts. It's truly helped my system become not only more realistic but more detailed.

Actually tidally locked planets rotate, they just rotate at the same rate that they make a revolution. That is why this planet does have a North Pole, just like our moon does. Where it is just depends on axial tilt. Orbit is indeed possible, though I'm sure it would be eccentric. I hadn't considered it too big of a problem... The real problem, I realized, after these theories got me doing more research, is that unless the moon was close enough in mass by a factor of 10 it would either fall into the planet or the sun at some point depending on which orbit was faster (which is in agreement with Raptori's theory except that larger moons actually are more sustainable.) The real problem here is just that a very big moon would probably cause the objects to become tidally locked to one another - a great idea for a different planet project, but alters this one too much.

I figured some kind of collision would have been the reason for the moons, but if they'd be falling into the planet eventually, I'd rather scrap them, however, it seems interesting that two similarly sized objects can be tidally locked to each-other and orbit a sun... I -could- go with my collision idea and say that once there were two worlds orbiting one another, which is a scenario that would give life an earlier chance to get started, too (wider habitable zone from day/night.) Let's say a disaster broke up the sister planet, creating a few moons, either destined to someday coalesce into a large enough object to hold orbit, or eventually fall into the sun. The recent-ness is really not a big issue, since in astrological terms "recent" can give or take hundreds of millions of years. My ancient sentient race is only a tenth of that age. Life could have survived such a bombardment and still be very diverse at present, (Die-offs actually promote evolution, by opening new niches for more and more complex organisms to fill.)

But I digress, if most of the debris was propelled at a trajectory that sent the largest chunks of the sister planet into the sun, leaving smaller bits to shower our host or coalesce back into the biggest remaining chunk of the sister, then it might work out for life. The moon might still be large enough to orbit for a good while if, like Raptori says, it's close enough.

This would cause some strange things to happen, but I think they might be beneficial. The tides would be very aggressive and stir up the sea a bit, good and bad... There might even be a noticeable change in gravity depending on where the moon is at, just fun... I assume the planet would stay locked to the sun but it would wobble distinctly. This would actually help create more dynamic weather, and keep hot spots from being too extreme - the desert in the center might not actually cook flesh off bones. (Otherwise, my world doesn't have a big enough liquid sea to have a lot of ocean current and distribute heat.) The moon would have to be just the right size, though I'm confident that size exists, whether I figure it out or not. In conclusion, it doesn't really matter if the moon will stay in orbit forever, because neither will our own, after all.

[Podcreature]

Also, there's really no reason to expect the hot side to be all land, is there? There'd be no ice given the model you're using, true. But there might be a sea crossing the hotside pole. Land might run right up to the ice sheet in some spots. Etc. Because, yes, the planet would be pulled into a bit of an egg shape, but that tidal force is acting on the water too, so you can model it as a flat surface. High points are high, low points are low (and full of water, which is rapidly evaporating at the hotside pole).

Thanks for the thoughts on navigation. Ideas are welcome, as I have yet to settle on something that will work for future maps... should I work up the nerve to make one that's detailed, and I'm hesitantly tempted.

To answer your question, I wouldn't say I "expected" it to be all land when I made it that way. I guess it's just fun to embrace coincidences. Not to mention, I do prefer my land organisms to have more real-estate to compete over. I decided that this world looks this way specifically because I just imagined this large continent on the face, and erosion along the glacial melt zones made a cookie cutout of the warm region. But here's some reasons it might look the way it does... aside from coincidence/preference: Most of the ocean is frozen on the back side of the planet, keeping sea-levels low on the face. Rain falls frequently along the "green band" and erodes the earth there. When glaciers melt water pools in the depressions they made. So it's a cookie-cutter concept, basically, and water is the cutter.

[Nexis]

HI.

I was reading this thread and had a thought. Depending, of course, on the planet having a small or large elliptical orbit. This may cause sun watchers to see the sun "Beat like a heart" in a year. This may have more theological implications than navigational.

The other idea comes from Eratosthenes. The scholar who measured the circumference of the world by measuring the path of the sun by studying the shadow of a stick. If you place a stick directly under the sun at 90 degrees from the ground it would cast no shadow. Moving away from that stick and place another, it would cast a shadow directly away from the center under the sun. Do this in a circle and farther away you can have a very accurate navigation instrument and mapping. Carrying a "Sun Compass" will tell you how far away you are from the "Sun-ward" center of the world and the direction of the shadow will always point in that direction. That will create a compass if you standardize the height of the stick you can measure the distance away you are from "Sun-ward" by measuring the length of the shadow. Say If you want to reach the city of Randar you must travel North- East of sun-ward for seven shadow lengths. North south east and west generally being directions away from the Sun Center of the world.

[Podcreature]

I actually was thinking of having an elliptical orbit for the sake of temperature flux basically seasons, but they'd be on a 2 month cycle, lol. May be worth it, but the "pulsing" sun would be really neat.

And that is the best example of navigation on a planet like this I've heard yet... or at least for a very specific navigation tool that incorporates the planet's tide-locked status. The length of the shadow would definitely be the key there. Would have to maek sure it's level though. Maybe you could wear it on your wrist like a watch, and it could be a little globe, or flattish orb, water filled, so the plate inside stays level, and in the center of the plate is a little needle or something. This wouldn't have to be very big at all. With the direction of the sun and the length of the shadow, you could know exactly where you are at any time! With this and a map you'd be set.

UPDATE: Well I did a little mooore research and apparently the orbit of our planet is eccentric, but slight flux in distance from our sun has very little to do with our seasons. I kindof already knew it had something to do with Axial tilt but didn't know which played more influence. (Wasn't as interested in this stuff when I was in school, lol) So... I'm thinking this planet will have some kind of axial tilt, because seasons will be very helpful for life, but it will cause the sun to change position notably. So to navigate with such a thing as a sun-dial, you'd need to know the season, too I guess. Currents and dynamic weather can actually increase the size of the green band considerably... I wonder if an eccentric or elliptical orbit really would cause noticeable change in sun's appearance.

In conclusion, this planet will probably have an equator, a minuscule elliptical orbit (since it was probably two planets orbiting each-other and one was lost, disrupting a perfect circle slightly) and most likely an axial tilt, since scientists think the collision that produced our moon was the cause of Earth's. There are magnetic poles but I wonder if the sun will still be useful in mapping too if it moved in the sky a bit. Might need a map for each of the 55 days in a year.

And here's the finished chart, I'm basically done with this for now... until I decide to update the planet's topology, and create a real map with political and climate information. (The moon isn't that small, it's not orthographic view, it's how big it actually looks from the planet.)

finished chart.png