The book I’m reading takes place on a planet in which the seasons follow a winter-spring-summer-fall pattern, but the seasons are unpredictable. Any one season can last years, and there’s no telling how long it will last; a winter lasting 10 years is not unheard-of. And Winter Is [always] Coming.
Under what circumstances would this be possible in real life (if at all)? Would an extra moon or two, a weirdly-shaped orbit, or any other geophysical/astronomical factors create such a situation?
You can have a variable sun.
I thought about this in connection with a particular tv show and the only thing I could come up with was a large, unstable belt of debris in the same ecliptic plane as the planet that would be massive enough to obscure radiation from its star.
Image something like the asteroid belt in this solar system but a couple orders of magnitude bigger. Depending on the distance to other bodies in the system and their mass, the debris in the belt would constantly be clumping and being remodeled such that the planet in the OP could end up parked behind such a clump (or vacancy) for very variable periods of time.
I imagine we’re talking about the same thing.
Game of Thrones?
This is trivial: you have a binary system where one star has a highly elliptical orbit of the other. Brian Aldiss did this with Helliconia.
If the Earth had no moon it wouldn’t spin steadily on its axis the way it does and would wobble from a nearly straight up 0 degree tilt to a nearly on its side 80 degree tilt, which would cause seasons to vary so wildly as to make parts of the planet randomly equatorial and arctic. If there was a planet with no moon that varied randomly between having the axis of the planet point towards and away from the sun just enough to make it summerlike and winterlike conditions due to other varying gravitational forces in the solar system maybe such a thing could be possible, but I couldn’t guess at what the specifics would have to be.
In the actual instance mentioned: Magic.
Apart from the answer of magic, how would you distinguish between spring and fall? Can spring follow fall and vice-versa? How are they different?
Yes. I think there was an article on IO9 but I don’t remember if they had anything good. This was maybe 6+ months ago though.
Clearly, spring is a season in which plants emerge from dormancy for their reproductive activities, and fall is when they begin to shut down. You’d know the difference in these seasons by the activity of the plants.
Supervolcanic activity could dump particulates and gases into the upper layers of the atmosphere, causing winter-like conditions for years at a time. This could be happening on one continent while people try to survive the seasons on other landmasses.
If they are that unpredictable they are not really seasons. The planet just has unstable climatic conditions. The whole concept of a season has to do with regularity and predictability.
I’d guess that a sufficiently elliptical orbit would do the trick, in conjunction with the prototypical axial tilt. Most people think seasons come from the former, and not the latter. Then again Mars has such an orbit, yet IIRC its seasons are as regular as ours.
Back to the OP, it’s hard to imagine a planet with life (as we know it) if there are winters that could last for 10 years, and springs and other growing seasons that only occur at random times. Plants (as we know them) require some degree of regularity to grow as producers. Of course, it’s fiction, but the question presumes a semblance to known systems, i.e our own.
Not to mention that everybody in Westeros and Essos seems to measure time in something called a “year”; which even appears to be more or less the same length as an Earth year. Equally odd is that one of the signs the Maesters used to determine that “winter” is coming was that the days were getting shorter; which is a clear sign that the planet’s axial tilt does change unpredictably.
The year part is hard to wrap your head around; as I understand the story (yeah, I don’t know, I’m that guy) winter and summer both come on randomly and last many of our own years. It seems like an elliptical orbit would explain the long seasons but not the randomness, but an Earth size orbit would be too small to explain why the axis was pointed mostly directly at the sun for many revolutions. Maybe the orbit is much, much larger and it actually takes many Earth years to complete a revolution, also meaning the star is much hotter, also meaning that random gravitational forces are yanking the axis into angles within 45 degrees af directly pointing towards the star for years at a time. If that were the case the only reason to refer to an Earth “year” is if the inhabitants came there from this Earth.
This isn’t even remotely true. Even if you take the studies of Jacques Laskar (which is where I assume you got this idea) at face value, even the instabilities that are predicted still occur on geological time scales, not in the span of years or even decades. Note that the other planets with no large moons in comparison to the planetary mass, such as Venus, Mars, Jupiter, Saturn, Uranus, and Neptune have not been observed to “wobble” (precession of the ecliptic) in the periods in which they have been observed. It is true that Mars is believed to undergo a substantial precession of the ecliptic, but this probably has more to do with being geologically inert. The primary advantage of the Earth garnered from its Moon is that due to the additional stored energy of the Earth-Moon system it is relatively insensitive to perturbative effects on its orbital characteristics such as ecentricity by Jupiter compared to a world without a large moon. However, again, these effects would occur on geological timescales.
Other influences due to eccentricity of orbit, additional companions to their primary star, et cetera would have secondary effects which would also be noticable; for instance, days becoming significantly longer or shorter, constellations shifting, et cetera. A more likely hypothesis is that the composition of the upper atmosphere (comparable to our upper troposphere and stratosphere) undergoes dramatic cycles which alter its permittivity and absorbtivity, allowing more or less radiation to the lower troposphere and the oceans, which then alters the planetary climate. Alternatively, there may be some process in the oceans which changes in current speeds or directions occur (for instance, changes in density that drive thermohaline currents) or the release of undersea hydrates such as methane clathrate. Or perhaps there is some significant source of supplementary geothermal heating which goes through irregular cycles.
Stranger
One problem is to consider how advanced the astronomical and meteorological knowledge of the planet’s inhabitants is. If they are “cave men”, sure, they might not be able to see the pattern, but an advanced civilization, even one as primitive as Ancient Greece*, might be able to either find the greater pattern (e.g. the seasonal patterns change over a 165 year cycle), or identify what astronomical bodies are associated with climate change (e.g. when Mars starts appearing close to Jupiter, expect longer winters ahead. When Mars appears alone in the night sky and Jupiter is nowhere to be found, expect long summers ahead).
*They weren’t actually that primitive, they had the steam engine and coin operated vending machines!
One thing a moonless Earth wouldn’t have would be tides at the level we see. The only meaningful tidal effect would be solar, potentially having an effect on the life there. Tourism in the Canadian Maritime Provinces would suffer some.
Come on, man, give me a break, I’m trying to come up with possible explanations for comic book logic. I guess I shouldn’t have said “seasons” since the Earth wouldn’t be shifting around within a solar year, or even a century; I didn’t mean to imply that without the moon the planet would be straight up one week and lying on its side the next. Sheesh, you must be a blast to shoot the shit with at all the rocket scientist parties. 