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Planet-Wide Seasons? (Random Planetary Orbit Question)

 
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Shatner
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Joined: 07 Mar 2008
Posts: 867

PostPosted: Wed Aug 16, 2017 4:11 am    Post subject: Planet-Wide Seasons? (Random Planetary Orbit Question) Reply with quote Add User to Ignore List

I had something I was wondering about that I thought I'd pitch to y'all in case someone here had any insights.

The seasons on Earth are due to an axial tilt in the planet's spin. Our blue ball is a little over 23 degrees off with respect to the orbital plane, which means one hemisphere is getting more sunlight than the other. Hence seasons, the severity of which increase the farther you get from the equator.

Now, imagine you had a planet with no axial tilt. No tilt, no seasons... right? Well, yeah in an orbit with little-to-no eccentricity. But, and this is me finally getting around to my question, could you have a planet with no axial tilt but a highly elliptical orbit that experienced seasonal temperature variation due to its variable distance from its star?

If so, what you'd have is planet-wide seasons, with literally world-wide winter and world-wide summer, which is kind of neat and would give rise to some really crazy weather and evolutionary results.

I mean, the whole thing is fantastical since a world like that should be well outside the Goldilocks Zone for at least some of its orbit and be subject to nasty impacts, to say nothing of what merry hell the rest of the system's orbital bodies would do to something with such a huge, elliptical orbit, but I'm willing to handwave all that stuff aside for this asinine curiosity.

So yeah, thoughts?
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FrankTrollman
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Joined: 07 Mar 2008
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PostPosted: Wed Aug 16, 2017 4:37 am    Post subject: Reply with quote Add User to Ignore List

Comets are basically planets that have planetary-wide seasons in exactly the way you describe. They glow when they are near us because they get close enough to the sun that the ice heats up and melts. In essence they are in winter when they are far from the sun and summer when they are close to the sun.



-Frank
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Mechalich
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Joined: 04 Nov 2015
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PostPosted: Wed Aug 16, 2017 8:31 am    Post subject: Reply with quote Add User to Ignore List

You could also have planet-wide seasonality if the planet was in a multiple star system, which is the premise of the Helliconia novels.
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deaddmwalking
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Joined: 21 May 2012
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PostPosted: Wed Aug 16, 2017 1:06 pm    Post subject: Reply with quote Add User to Ignore List

I don't think you'd have to have a very eccentric orbit - for example, you wouldn't have to go as far as Mars, even.

I'm not sure on my math, but if you double the distance from the sun, you'd get 1/4 as much light (and therefore heat). Mars is 1 1/2 times as far from the sun as the Earth, and the mean temperature of -55 Celsius is 73% of the average temperature of Earth 14 Celsius (I converted to Kelvin to compare).

The difference between an Alaskan Winter (5 degrees F) and the average temperature at the equator is 86%.

Since you want roughly half the climate variation as exists between Earth and Mars, you want roughly 1/4 of the distance between them. The Earth would range from 91 million miles to 104 million miles.

Mars is the most eccentric planet with a distance of 27 million miles between it's closest approach to the sun and it's furthest. Earth would be slightly less eccentric than Mars is now.

Someone with a better background feel free to correct my numbers.

Edit - And I realize I completely disregarded the effects of atmosphere. Since it effectively traps heat, it would take longer to cool off a planet so the distances would probably have to be much more significant.


Last edited by deaddmwalking on Wed Aug 16, 2017 1:29 pm; edited 1 time in total
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DrPraetor
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Joined: 02 Apr 2009
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PostPosted: Wed Aug 16, 2017 7:06 pm    Post subject: Reply with quote Add User to Ignore List

deaddmwalking wrote:

Someone with a better background feel free to correct my numbers.

Edit - And I realize I completely disregarded the effects of atmosphere. Since it effectively traps heat, it would take longer to cool off a planet so the distances would probably have to be much more significant.


You failed to account for the atmosphere, but you also failed to account for differences in orbital velocity - the planet would be moving more slowly over a longer distance when further from the sun, so heat retention by the atmosphere would be counteracted by spending a (considerably) greater amount of time in the colder part of the orbit.

If I were writing a science fiction novel, to a first approximation I'd hand-waive the effects into cancelling out, but in any case, your winters would be long and your summers would be short.
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