Effect of axial tilt on a planet

[JamesDJarvis]

-- our moon is roughly 25% of the mass of the Earth. .

nope. Way off there.
The Earth has a mass of 5.98x10^24 kg and the moon is 7.35X10^22 kg.
The moon is 1/81 the mass of earth.

The moon would have to be made of some pretty heavy metals to be 1/4 the mass of earth.

 

[JamesDJarvis]

Why do folks think earth and mars are almost the same size?
Mars is about 1/2 the diameter of the Earth. That means it has about a 1/4 of the surface area earth does (roughly speaking).

 

[Aristotle]

Why do folks think earth and mars are almost the same size?
Mars is about 1/2 the diameter of the Earth. That means it has about a 1/4 of the surface area earth does (roughly speaking).

But, from what I've read, the surface are of mars is about the same as the exposed surface area of the earth (i.e. everything not covered by water).

 

[lgburton]

I know what you are saying. The whole planet is supposed to be hot so I have the heat (I see that poses a problem too, but we'll get to that later). Water is obviously the primary issue with my land planet idea. My question is, does the water need to be oceanic in depth? Let's say my "swampland", which is mostly flooded with large boggy archipelegos here and there, covers 20% of the planet. Sure, there are large portions of it that are only 10 to 50 feet in depth, but I could see there being large canyons 3 or 4 hundred feet deep scarring the surface beneath the water. Perhaps it's even fed by additional sources of underground water. In a sense it becomes a shallow, stagnant, ocean without tides. Which reminds me, did I mention the lack of a moon?

well, no you diddn't, but it wouldn't have as signifigant an impact as has been implied earlier in this thread. having checked up on it, the science that the tv shows were using is relativly new and unproven. the real fact is that we don't know what impact a large moon has, aside from tides, on a planet.

anyhow:
i'd say that you do need oceanic depths to produce the heat-sink effect that our oceans do on earth, helping make a viable hydrosphere. if you are going to go with the swamp/deep canyon route, i'd suggest making them equatorial, so that they can still function as heat-sinks.

Let's say my rivers and lakes/seas cover another 5%. Am I anywhere even passably close to being "acceptable if not improbable" at that point? You're right, saying it's magic is likely the easiest approach, and to a point I'm doing that. I don't expect my land planet to be scientifically feasible so much as I want it to be believable at first pass.

I was also playing with the idea of massive geyser fields in areas of significant seismic activity constantly pumping vapor into the air.

well.... the ammout of water that a guyser field, no matter how large, would put out wouldn't be that signifigant in terms of cloud formation / greenhouse effect, when compared with oceanic evaporation. i could be wrong on this point, but...

just my 2cp on the world building:
well, with what you've got so far, i'd arrange the geography so that the equator was mostly swampy on the outskirts, with a narrow but world-spanning sea covering most of the tropics. if this area were the primary volcanic area, you could have it so densly filled with islands that it wouldn't be too much like an ocean... it could make some interesting societal myths/legends, would give you the required water area to produce an active and (most likely) life-producing hydrosphere.




and, just in case anyone wanted scientific backup of the snowball effect i was talking about earlier...
http://www-eps.harvard.edu/people/faculty/hoffman/snowball_paper.html

 

[lgburton]

Why do folks think earth and mars are almost the same size?
Mars is about 1/2 the diameter of the Earth. That means it has about a 1/4 of the surface area earth does (roughly speaking).

surface area, earth does win, hands down.

LAND surface area, however, if you were to use an arbitrary altitude on mars which would fill the northern basin, hellas, and vallis noctis/marinaras, mars comes out about the same, because only 30% of the surface would be covered in water, as opposed to earth's 70%.

 

[JamesDJarvis]

surface area, earth does win, hands down.

LAND surface area, however, if you were to use an arbitrary altitude on mars which would fill the northern basin, hellas, and vallis noctis/marinaras, mars comes out about the same, because only 30% of the surface would be covered in water, as opposed to earth's 70%.

That'd mean this flooded mars would have 61% of the land area of earth. Not close enough for "about the same" in my book, if you don't think so don't take my word for it pour two little kids some drinks but give one 61% of what you give the other one and ask them what they think.

 

[lgburton]

That'd mean this flooded mars would have 61% of the land area of earth. Not close enough for "about the same" in my book, if you don't think so don't take my word for it pour two little kids some drinks but give one 61% of what you give the other one and ask them what they think.

...where are you getting your measurements from, out of curiosity?

now, on another level, i'm also wondering where your original question came in - i don't really see anyone in this thread assuming mars is anywhere near the same size as earth....

 

[JamesDJarvis]

But, from what I've read, the surface are of mars is about the same as the exposed surface area of the earth (i.e. everything not covered by water).

If you are getting sceintific about what biomes would be where you really can't just shove the oceans aside. certainly not when you are talking about climate and weather. The oceans are 70% of the earths surface area and as such have a huge impact on climate. There is weather over the oceans.

 

[lgburton]

If you are getting sceintific about what biomes would be where you really can't just shove the oceans aside. certainly not when you are talking about climate and weather. The oceans are 70% of the earths surface area and as such have a huge impact on climate. There is weather over the oceans.

well, thanks for pointing that out. i read it in a different way, though the way you read it is definetly still valid.

however, if you'll note, a lot of the discussion has been about why oceans are really needed for a planet to have created life... so yes, those of us discussing the problem are aware that they have a huge impact on the climate, and that weather does indeed exist offshore.

part of what's going on in this exersize is trying to figure out a way in which, while minimizing oceans on a planet, to still have things like rain and weather.

do you have something constructive to contribue to the conversation?

 

[Aristotle]

If you are getting sceintific about what biomes would be where you really can't just shove the oceans aside. certainly not when you are talking about climate and weather. The oceans are 70% of the earths surface area and as such have a huge impact on climate. There is weather over the oceans.

Yep, but all of my comments (and pretty much all of the mars talk in this thread) have revolved around the idea of a planet with significantly less water coverage than the earth. 25% surface coverage by my most recent post, and not nearly as deep as the oceans of our own planet. It's bee pointed out to me, on several ocasions, that such a planet isn't really feasible given our current understanding of how planets work. All I'm looking to do is make my idea slightly more believable. The bad science will likely be obvious to those who know what they are talking about, but will hopefully be enough to suspend disbelief for for folks who are willing not to look too hard. Past that point, "It's magic. The core of the world is the corpse of the first god too, so you had to expect a little scientific inconsistancy."