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In this link, the BA himself debunks a website that claims that Earth's axis has tilted to 50 degrees. Needless to say, it would be a bizarre place.
My question is this: If you had a planet that was the same as Earth in every way, except that the axial tilt was 50 degrees, what effects would the extended tropics and midnight suns have on the life on that planet? I'm having trouble imagining it.
- Maha Vailo
Order of Kilopi
The polar circle would be in the tropics! :surprised
Snow would be a world wide phenomenon and the poles would be very, very cold.
Established Member
No, the poles would be considerably warmer on average than they are now, possibly warmer than the equator. 50° is close to the point where the poles become warmer than the equator, though the distribution of the continents matters. See Habitable Climates: The Influence of Obliquity, arXiv:0807.4180.Originally Posted by Argos
Order of Kilopi
Not warmer than the equator, I say.
See Habitable Climates: The Influence of Obliquity, arXiv:0807.4180.The Sun would never be higher than 40 degrees at the poles, for a brief period, since the Sunīs declination would vary more rapidly from day to day.High obliquity planets have severe climates, with large amplitude seasonal variations, but they are not necessarily more prone to global snowball transitions than low obliquity planets
But maybe the poles would not be as cold as I first imagined, since tropical waters would cover a big percentage of the planet. The overall temperatures of the planet oceans would be lower, perhaps.
Established Member
Actually the solstice is when the Sun's declination is varying the least.
I'm glad you withdraw your assertion that the poles would be much colder than they are presently. If you look at Spiegel et al. figure 5 you will see that in the 60° model there is net heating at the poles and net cooling near the equator, and therefore heat transport from the poles to the equator. This is the opposite of Earth's current situation. The paper I referenced does not state where the exact cross-over occurs, but from memory it is between 50° and 60°, so the expected average temperature at the equator in a 50° world would be only slightly warmer than the poles. The distribution of the continents makes a difference. Land reflects more radiation than does the ocean, so, if there were ocean at the poles and land at the equator, the 50° world's equator could well be cooler than its poles. To model a real planet's climate accurately you would also have to take account of the effects of the continents and mountain ranges on the oceanic and atmospheric currents.
On a 50° world seasonal variations would be greater everywhere, but variation in average temperature with lattitude would be smaller. Global average temperature depends on the global heat balance. It's not obvious how changing the obliquity would change this, unless it precipitated a transition to a global snowball, which Spiegel et al. don't think is likely.
Established Member
Why is there no planet with a zero-degree tilt? Is no tilt even possible?
Order of Kilopi
The perturbations on Earth are a rough and dirty multibody situation, unlike the simple forces on a thought-experiment gyroscope. In addition our planet is lumpy and gooey, unlike the uniform rigid disk of a laboratory gyro.
Established Member
So, what is it? A very warm planet, or a very cold one? Also, what lifeforms might dominate?
- Maha Vailo
Established Member
Simply changing the obliquity will not make a planet very warm (hot Jupiter-like) or very cold (Neptune-like). If the planet starts with the current terrestrial biota (which is implied by same as Earth in every way) then I'm pretty sure the dominant lifeform would continue to be homo sapiens. In general tropical forms would do badly since such a planet would have no zone which is continuously warm. Terrestrial life would be much harder hit than marine life, because the seasonal temperature swings would be much greater on land than in the oceans, and migration is more difficult for land based creatures.
Established Member
So, what would essentially dominate on a terrestrial planet with high obliquity would either be desert life or steppe/prairie life. Feel free to correct me if I'm wrong.
- Maha Vailo
Order of Kilopi
I expect the predominant effect on these sort of planets would be the transfer of heat energy from the hot pole to the cold pole. In summer, the hot pole would get very hot, and the cold pole should be very cold (but the atmosphere will transfer heat from the hot pole to the cold pole). This would probably make the planet windy, in summer and winter at least.
During spring and autumn, the climate might be a little more like the Earth, and the whole planet might have a reasonable temperature and climate. But in summer, the hot pole will have weeks of continual sunshine, sometimes with the sun quite high above the horizon. That heat should be enough to prevent the buildup of permanent snow caps, unless the planet is in the cooler part of the habitable zone.
A very tilted planet, at 90 degrees, say, would be something like a cross between a tidally locked world and an ordinary world. At the solstices the atmopsheric circulation would resemble the asymmetric circulation on a tidally locked planet, and at the equinox the circulation should resemble Earth's circulation to a certain extent.
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The poles would have hotter summers and colder winters than now.
Winds to and from the equator would be stronger.
Birds could migrate more easily and humans too using wind powered boats.(have they been invented yet?).
Wind powered electrical generators would produce more output.
Seasons would be more extreme so live underground in an all electric house.
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Umm sails....
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So what you're saying is the winds would make sailing ships more efficient (thus possibly extending the Age of Sail on this alternate Earth), but you're also saying that the winds would force us to live underground (probably constraining civilization to hills and mountains). Doesn't this sorta contradict each other? It's pretty hard to get access to the ocean from a mountainside.
- Maha Vailo
Banned
We'd see much the same as we see on Earth today. The only difference would be where the various regions are located.
Order of Kilopi
There would be windy seasons and relatively calm seasons; you might want to live underground during the windy seasons.
Here are three images I've made using Celestia, showing the different seasons on an imaginary planet with a high tilt;
This one shows high summer in the southern hemisphere, with the local star nearly overhead and surface temperatures at the poles of 60 celsius and above; hot winds redistribute the heat to the rest of the planet
http://www.orionsarm.com/im_store/Silenussouthsumer.jpg
Here is high summer in the northern hemisphere- similar conditions apply
http://www.orionsarm.com/im_store/Si...orthsummer.jpg
Spring in the northern hemisphere; there is still snow on the ground in the northern hemisphere, so the albedo in that hemisphere is higher- spring is therefore cooler on Silenus than the autumn
http://www.orionsarm.com/im_store/silenusclouds.jpg
otherwise weather patterns in spring and autumn more-or-less resemble those on other Earth-like planets.
Last edited by eburacum45; 2009-Jul-25 at 04:20 PM.
Established Member
^ Wow. What sort of life could dwell in such harsh conditions? It seems like even desert life would have a hard time getting a foothold, much less human life.
- Maha Vailo
Order of Kilopi
Some sort of biannual plant that only appears in spring and autumn and low, sprawling animals that can tolerate windy conditions might survive best.
Established Member
Also in little islands climate will be much softer.
Newbie
Those who have trouble visualizing the effects of pronounced tilt might go and have a look at my site: http://www.planetfuraha.site. Choose the planet icon, below the galaxy icon, and choose 'some more examples'. You will see how light and day vary on the surface of a planet with a 43 degree tilt.
Not quite 50, but close enough.
Order of Kilopi
I like the page that shows 'Furaha Today'; is that updated automatically, or do you do it manually?
Newbie
Automatically, with Javascript.
I learned only enough of it to read time and calendar data, and used a little bit of mathematics to work out wghich of a series of figures to use. The only thing that is done by hand is to upload fresh files for one or two months beforehand (those could all be left in place, but they take up much room).
Order of Kilopi
Very nice.
Established Member
--Sea level would be higher; the polar climate wouldn't be stable enough to build up continental ice sheets. This would moderate the biggest climate extremes.
--As aforementioned, seasonal weather would probably be much more violent than ours, with stronger winds at all levels.
--Assuming the Moon's orbit was the same, the full Moon would frequently below the horizon during summer nights in the upper mid-latitudes (from say, London) while being near the zenith during the winter.
--I'm guessing biodiversity would be less; highly changeable environments on Earth typically have relatively low diversity (e.g., estuaries, tundra, taiga, etc.), even if they have high biomass (again, the example of estuaries). Of course, evolution would perhaps be "forced" to become more "inventive" in such a scenario, so there's no way to say for sure.
Order of Kilopi
I would imagine even more creatures would aestivate and hibernate during the extreme summers and winters and/or migrate further north and south.
Order of Kilopi
A couple of papers on obliquity here
http://arxiv.org/abs/1101.2156
http://iopscience.iop.org/0004-637X/691/1/596
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