Effect of axial tilt on a planet

[Umbran]

Yes. Because of the air pressure and temperature water can't really spend much if any time as a liquid.

But is that a cause of the problem, or merely a symptom of another cause? Recall that the planet probably hasn't always been the way it is now. The reasons it has no liquid water now may not be due to it's state now, but instead upon it's state in the past...

For example - Olympus Mons notwithstanding, Mars doesn't seem to be a tectonically active world. Right now, vulcanism is seen to be a big refresher of atmospheres. Without active volcanoes releasing gasses, you eventually end up with a thin atmosphere as gasses escape to space.

So, maybe lack of vulcanism is the problem, right? Well, one might say that Mars is tectonically inactive because it lacks a large moon. Large moons produce tidal friction heating in their planets, keeping their cores warmer for longer. So maybe the lack of the moon is the problem.

But a large moon is not the only thing to keep a planet active. Radioactives in it's core also do a large part of that work. So, perhaps the planet has no life because it has no water because it doesn't have enough of these heavy radioactive elements...

Or, as is usually the case with nature, there's no one single cause for anything. End results come through the confluence of many factors, not one.

 

[Warehouse23]

Harmon--to answer your question: there is some compelling evidence that Mars has lost water (in addition to other light gases) over time. This process is part of a phenomenon called "sputtering, " or "Jeans Escape." As gas molecules, like water vapor, bounce around an atmosphere, they may reach an altitude where there are so few neighboring gas molecules that at any given moment they may bounce outwards, away from the planet, and not encounter any additional gas molecules to bounce them back planetwards (think of this like billiard balls on a pool table--if you take the bumpers off the sides of the table, the only thing which would keep a ball from rolling off the table, and onto the floor, would be a collision with another ball).

Water cannot "evaporate" from a planet--evaporation is just a state change between liquid and gas phase. Water, hydrogen, helium, and other gases can escape from planetary atmospheres, though. The hotter you get the particles (by solar heating, a greenhouse effect, what have you) the larger the gas molecules you can eject.

 

[Ferret]

Well I don't know about the variables of the satalite around the brown dwarf, well I haven't decided them. I'd still like the eclipses to be rare but at least 1 a year, the heat delivered shpould be negligible, by reasonable do you mean reasonably close? I wasn't sure I needed the satalite to not be tidally locked, I just wanted it to get enough light all round; no light and dark side. I realise as it moves around the planet it's going to get odd light and day periods. Axial tilt is similiar to earth, no idea about the orbit, I know it would change seasons and stuff on a planet (I think) but in terms of a moon ???

Josh, what are the alternative for planets though? I know next to nothing about planet types. Would the heat radiation be very bad? Would it actually being tidally locked cause a light and darkside? I can only imagine that with a planet.... And wouldn't heat/light from the dwarf cancel/dull the effects? Why is it in such a hot zone? What effect would the distorted field have? Taffy you say? how do I counteract this? Larger hard substances inthe material? Further out? And alternative to a weighty brown dwarf, something lighter?

Yes, the poping of someone who knows better would be very good

 

[Harmon]

Water cannot "evaporate" from a planet--evaporation is just a state change between liquid and gas phase. Water, hydrogen, helium, and other gases can escape from planetary atmospheres, though. The hotter you get the particles (by solar heating, a greenhouse effect, what have you) the larger the gas molecules you can eject.

Evaporate was the only word I could think of that would get my question across.

Its been a long held theory between my Mom and I that Mar's water escaped its atmosphere through the lack of a thick atmosphere (neither of us has the education to have theories on anything- Mom told me of her first theory back in the late '50s that the continents had all once been one major continent, turns out she was right. She and I saw our first pictures on Mars in the early 80s and said- "had an ocean, gone now," months or years before I heard about it. I have a theory on time and gravity that I have been told conflicts with Albert's so it must be wrong. Sorry, hijacking the thread- forget I was here.)

 

[Desdichado]

Josh, what are the alternative for planets though? I know next to nothing about planet types. Would the heat radiation be very bad? Would it actually being tidally locked cause a light and darkside? I can only imagine that with a planet.... And wouldn't heat/light from the dwarf cancel/dull the effects? Why is it in such a hot zone? What effect would the distorted field have? Taffy you say? how do I counteract this? Larger hard substances inthe material? Further out? And alternative to a weighty brown dwarf, something lighter?

Well, a big part of the fun of having the planet be a satellite of a gas giant or brown dwarf is so that it can have a big glowing and striated feature in the sky that looks really cool. The only problem is, to have a reasonable chance at habitability you need to be a bit farthur out, which somewhat minimizes the impact of that. Personally, I think that's something that can in good conscious be modified for dramatic effect, but I'd never do that without knowing the implications, myself.

As for the heat, no, that's not necessarily a problem. If anything, it means that you can move the entire system farthur away from the star, because if doesn't need to get all its heat from the sun anymore. Being tidally locked doesn't mean that there's a light and a dark side; it means that the brown dwarf will always be in the same position in the sky; it will never rise and set. But the sun still would, and presumably that's what's causing your day and night. Of course, that's where I start losing control of the mathematics of the model, when I have to try and calculate all the effects of rotation around the brown dwarf, the brown dwarf's rotation around the sun, and what all that does to seasons, days, years, etc. Also, if you are tidally locked and the brown dwarf is a significant source of heat, then you've got odd hemispherically dominated weather patterns; one hemisphere is significantly hotter than the other, meaning that prevailing winds far beyond anything in our own world will race around the surface of your world.

As for the tangled up magnetic fields; that's just a metaphor; the magnetic fields aren't actually strands that can get tangled. It's generally believed, though, that the disruption to the magnetic fields means they aren't effective at shielding from solar radiation.

So, it's all doable. I get a bit lost in the model when I try to calculate the effects of it, though. But if can be done, and you could probably handwave away most of the problems I've spelled out and few people would quibble.

 

[Harmon]

Edited- answer appeared after I posted this

 

[woodelf]

Sorry...that should have read primarily.

If you compare the seasons between the Northern and Southern hemispheres, you'll find that their summers and winters aren't as harsh South of the equator, and that's a function of eccentricity of orbit.

That doesn't pass simple sniff test. Southern hemisphere is tilted towards the sun at the same time that the Earth is closer to the sun. Northern hemisphere is tilted towards the sunwhen the earth is farther from the sun. So, if eccentricity were the factor, you'd expect the Southern hemisphere seasons to be more extreme, not less.

Either you're wrong on which has the more extreme seasons, or orbital eccentricity is overwhelmed by other factors.

 

[woodelf]

Cool question and great answers. I don't have much to add other than I wish I could have gotten some of you to reply to my "land planet" thread a while back. World design is so cool and I'd like to get more into the science of it, but haven't found much in the way of introductory material on the subjects in question.

• Magical Society: Ecology and Culture has some of this stuff
• Medea: Harlan's World is several hundred pages exploring the creation of a hard-science scifi world
• After Man: A Zoology of the Future has some really cool stuff in the introduction on th eevolution of life and interactions of geography and biomes and lifeforms.
• the world creation appendix of the AD&D Wilderness Survival Guide is actually a pretty decent introduction to this sort of stuff, if you have no background whatsoever.
• i hear good things about the MegaTraveller World Builder's Guidebook supplement, but i've never gotten my hands on a copy
• Aria: Worlds is absolutely phenomenal, though it pretty much deals with everything from society on up, only touching on biology and geography/planetology.
• Aria deals heavily with the metaphysics underlying all of this, as does The Primal Order and The Primal Order: Chessboards.
• After the Warming is a special on global warming produced around '90. It's fascinating to see how many of the predictions it made (which were at the time going out on a limb) have since been supported or even proven. It's also a really good introduction to the best understanding at the time of what drives climate and weather.
• The Galactic Expedition to Solar System M17 (not 100% on that title, and i can't seem to find my copy at the moment) is a fascinating example of a well-thought-out, but really fantastic, world. It looks like it's the basis for the recent Discovery Channel special Alien Planet, but i haven't seen it yet to be certain. On the down side, where this stuff is concerned, it's more about biology and ecology than geology and climatology.

Also, check the Writer's Digest and Science Fiction Writers of America offerings--i don't know, but wouldn't be at all surprised if they had some of this info.

Or, go get a relevant physics/astronomy/cosmology degree. That should cover it. ;-) [Apparently geology, too, though i wasn't aware that they tended to deal as much as Warehouse23 implies in speculative geology.]

 

[woodelf]

okay then...

I was working on a planet with no true oceans. A planet that was mostly land. I was thinking of making it small, say about the size of mars, so it would have roughly the same land surface area as the Earth. My concern was that I didn't want it to be a desert world or an ice ball, and those seem to be the most likely choices for the planet I am describing. I was hoping to find some science to explain why my world is the way it is. Of course the science doesn't need to be overly deep. It's a fantasy world and I'm fine with "it's magic" being the final verdict.

I was looking at including 4 primary biomes (there would be rivers, forests, and such in each as appropriate). There would be a large desert area with no seasonal change other than hot days and cold nights. I was guessing the best place for this was a pole (likely leaning towards the sun). There would be a vast grassland/savannah dominating a large portion of the world. It would be covered in seas of grass from two to six feet tall. It would be warm year round, with an annual wet season (possibly a cascading wet season since the area is so big?) that floods the lower plains. Then there would be a swamp area (swamps, bogs, everglades, or whatever) with a great deal of shallow standing water. And lastly there would be a large forbidding rainforest region. It would be warm year round with a short season of high heat. It would be littered with lakes and streams fed by near continuous rainfall.

Mountains and canyons are common throughout all 4 areas. Earthquakes are frequent and volcanic activity is fairly regular in remote locations. Rivers, some much larger than anything we have on Earth, can be found in all areas. There are many small and large rivers in and near the jungle and swamp areas. Fewer in the grasslands (except during the wet season), and only a couple in the desert. I figure many of them start in the mountains and the rainforest, and most of that water makes it's way to the swamp region, collecting minerals and becoming more and more brackish as it goes until it finally becomes unusable near the swamp area.

Uh... that's mostly it.

Well, if we just assume there's a mechanism to drive the water cycle, and therefore there are rains and rivers and so on [perhaps increased volcanism means more particulate matter in the atmosphere, maybe just on a seasonal, or at least cyclical, basis, and thus clouds condense more easily?], my first thoughts are:

• You need much less altitude variation. If there's enough water to form rivers, it's gonna run downhill and form lakes or oceans. If there's no "downhill", that won't happen. More reasonably, if you have large areas that are only slightly lower, instead of deep areas, you'll get swamps instead of oceans.
• Much higher temperature, year-round, keeping more of the water in the atmosphere, rather than condensed and on the ground. Thus more greenhouse effect, as well as less standing water.
• Minimal seasonal change implies equatorial, not polar. Equatorial regions have the least seasonal change in solar radiation intensity--and if you take out local moisture (as in a desert), this allows daily changes in solar radiation intensity to be as or more significant than the seasonal changes.
• Not sure how you have canyons, rivers, and no oceans without the canyons flooding. In our own world, canyons are dry, or only have a [relatively] small river at the bottom because there's other places much lower than them for the water to go to.
• I think your notion of really impressively vast swamp regions is a must-have. Picture something the size of the Mediterranean or Caribbean, but with an average depth of 50' or so--plenty shallow enough for anchored plants to completely fill.

Just some off-the-top-of-my-head thoughts, not all guaranteed to be correct or supportable.

 

[woodelf]

Well I don't know about the variables of the satalite around the brown dwarf, well I haven't decided them. I'd still like the eclipses to be rare but at least 1 a year, the heat delivered shpould be negligible, by reasonable do you mean reasonably close? I wasn't sure I needed the satalite to not be tidally locked, I just wanted it to get enough light all round; no light and dark side. I realise as it moves around the planet it's going to get odd light and day periods. Axial tilt is similiar to earth, no idea about the orbit, I know it would change seasons and stuff on a planet (I think) but in terms of a moon ???

Josh, what are the alternative for planets though? I know next to nothing about planet types. Would the heat radiation be very bad? Would it actually being tidally locked cause a light and darkside? I can only imagine that with a planet.... And wouldn't heat/light from the dwarf cancel/dull the effects? Why is it in such a hot zone? What effect would the distorted field have? Taffy you say? how do I counteract this? Larger hard substances inthe material? Further out? And alternative to a weighty brown dwarf, something lighter?

You need a copy of Medea: Harlan's World. Last i looked, i found several copies at Abebooks and Alibris for <US$10. It describes the creation of a collaborative world for scifi stories, and then a dozen or so stories set in that world. Some of the foremost speculative scientific minds of the time (early 80s) were involved in the creation of the world, so the science is as good as anything of the sort.

Medea is an Earth-sized world in orbit around a superjovian planet (right on the edge of brown dwarf status, IIRC). That planet, in turn, is in orbit aronud Castor C (a binary star system). [And, for added astronomical fun, Castor C is effectively in orbit around Castor A and Castor B, which are each binary pairs, and orbit one another.]