Effect of axial tilt on a planet

[JamesDJarvis]

...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....

Mars is about 6800 km in diameter. Earth is about 12750 km in diameter. You can get these numbers all over the place, accurate numbers actually.
The surface area of a sphere is 4pir^2. They are not spheres of course but close enough for scientific reality in fantasy worlds.


And i noted a few "about the sames" and had a silly online dweebish reaction.

 

[lgburton]

And i noted a few "about the sames" and had a silly online dweebish reaction.

totally understand that feeling... ;-)

 

[Desdichado]

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.

You're quite right -- I think I was getting the mass and the diameter confused.

 

[JamesDJarvis]

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?

You don't need rain to have weather. Variations in wind speed alone and pressure alone would produce differences in an environnment. Not much fun but still weather. Changes in pressure will cause changes in temperature (and vice versa). One air mass moving at a different speed compared to another air mass will also casue changes in pressure. when water gets involved weather is more fun.

The further a land mass is from a large body of open water the more likely it is to be dry.

How much water do you need for percipitation? The answer really only has to be some. If atmospheric pressure and temperature allow for there to be free standing water there is going to be evaporation, if there is evaporation the water vapor will eventually collect and form clouds which will result in rain.

Large bodies of water also serve to warm nearby land masses. The further you get from the water the more likely it is to be colder. Some glaciated regions of earth are effectively deserts made out of water because there is seldom any percipitation to speak of because what little there is adds to the glacier and doesn't reenter the environment as free water for some time.

Have a world without too much water and i'd say you'd have perdictable rain (not too much and not very often) with the seasons and time of day with an occasional surprise. Much like occurs in some desert regions here on earth.

 

[JamesDJarvis]

If folks want to play with this sort of thing I'd recomend hunting down "SIMEARTH" you get to tinker with planetary conditons, placement of land masses, amount of water and see how the environment turns out.

 

[Umbran]

,... if there is evaporation the water vapor will eventually collect and form clouds which will result in rain.

Not if there isn't enough water in total, there won't be. You need enough water in the atmosphere so that, on occasion, the relative humidity gets high enough for condensation to occur. It is possible to have a world with little enough water so that it can all evaporate, but the overall relative humidity to be low. That would mean no condensation, no cloud formation, and no rain.

Large bodies of water also serve to warm nearby land masses. The further you get from the water the more likely it is to be colder.

Half correct. large bodies of water serve to mitigate temperature swings - they warm the land in teh winder and cool it in the summer. The further you get from the water, the larger your temperature variation is apt to be. The highs will be higher, and lows will be lower.

 

[Harmon]

3) the reason that mars does not currently have life is still under debate in many different fields - but theories generally include the lack of liquid water, the high salinity of the soil, the fact that it's a signifigantly smaller planet, and the fact that it's twice as far from the sun as earth!

Question- could it be the fact that Mars has a thin atmosphere, that liquid water evaporated from the planet and that is why there is no ocean and thus no life?

 

[JamesDJarvis]

Not if there isn't enough water in total, there won't be. You need enough water in the atmosphere so that, on occasion, the relative humidity gets high enough for condensation to occur. It is possible to have a world with little enough water so that it can all evaporate, but the overall relative humidity to be low. That would mean no condensation, no cloud formation, and no rain.

well I was going with the assumption there is enough water on the world to have oceans and we aren't dealing with a brief "sweet spot" in an effectively non-terrestrial world when there is free standing water before it all gets trapped in the atmosphere as vapor or boils away forever.

 

[JamesDJarvis]

Question- could it be the fact that Mars has a thin atmosphere, that liquid water evaporated from the planet and that is why there is no ocean and thus no life?

Yes. Because of the air pressure and temperature water can't really spend much if any time as a liquid. When (and if) ice melts on mars it boils away into vapor. Not 100% certain but I think water boils on mars somewhere near 0 degrees celsius, which mean ice ->vapor but not ice -> water -> vapor.

The story might be different underground. A good point to hit for a RPG campaign.

 

[Desdichado]

You don't need rain to have weather. Variations in wind speed alone and pressure alone would produce differences in an environnment. Not much fun but still weather.

What, you don't think hemisphere spanning windstorms that wrack Mars for weeks at a time are fun?