# Seasonal progression for an Earth-like planet with wobbly axis tilt?

I'll try to keep this question as concise as I can, but I'm not great with technical jargon, so a simplified answer would be greatly appreciated.

Here's the set up:

I have binary star system with two yellow stars of equal mass orbiting each other. Around those stars are multiple planets, two of which are inhabited and share the same highly elliptical orbit (I'm imagining a football shape with the stars in the middle), but on exact opposite sides. One of these planets (A) is similar in axis tilt to earth, so I'm assigning it a similar seasonal progression (taking into account how the change in orbit will affect that), but the other planet (B) has an axis with more angle (something like 27 degrees, rather than Earth's 23) and their Milankovitch Cycle is considerably shorter as well (10,000 years, compared to Earth's 26,000), which I understand might impact the length and severity of its seasons.

Clarification: I'm using the word seasons not to describe the weather of an area, but more the amount of direct sunlight/warmth a part of the planet receives. For example, Winter Equinox in the Southern Hemisphere on Earth is when the South Pole receives the least amount of warmth/sunlight, which corresponds to the Summer Equinox in the Northern Hemisphere, where the North Pole receives the most amount of warmth/sunlight.

My research has lead me to believe that planet A will have a seasonal progression for each hemisphere more or less like the following:

• Winter 1 = Long and harsh
• Spring = Shorter than winter, very warm
• Winter 2 = Long and gentle
• Autumn = Shorter than winter, less warmth than spring

And the seasons would just repeat from there.

What would planet B's seasonal progression look like compared to this?

• You appear to be missing some seasons there. Welcome to the site, this is a good first question. – Xandar The Zenon Feb 17 '16 at 20:19
• Note that the L3 Lagrange point isn't a very stable location for a planet. Your system will likely destabilize very quickly. – Frostfyre Feb 17 '16 at 20:28
• how far are the stars from each other? – King-Ink Feb 17 '16 at 20:31
• How do you make the axis "wobbly"? And I think it will be on the scale of thousands of years, not really seasons. – JDługosz Feb 17 '16 at 22:24
• @JDĹ‚ugosz - That's poor wording on my part, I'm sorry. I meant that Planet B's axis will have a bit more of an angle than planet A (maybe 27degrees rather than Earth's 23), but also that the Milankovitch Cycle would change much more frequently as well (Earth's is 26,000 years, so this one would be... every 10,000 years, maybe?) – z2a Feb 18 '16 at 6:33

The climate and seasons will depend on:

## Dual-Star

A stable orbit implies no significant perturbation when getting closer from one star. It implies that the planets are far enough from both stars, which will appear very close from each other in their sky. As a consequence, the climate will not be impacted by the dual-star configuration: it will behave like a one-star system.

## Eccentricity

The earth solar irradiance fluctuates by about 6.9% yearly for an eccentricity of about 0.0167 (nearly circular). The orbit you describe is completely different, with a distance to star(s) likely to double. In this case, minimal irradiance will be 25% of the maximal irradiance.

## Axial tilt

Considering your orbit description, the effects of the tilt may fall short compared to the eccentricity impact : the tilt does not affect the total energy received, only it's local (planetary) distribution.

## Conclusion

The orbit you describe1 will lead to huge irradiance amplitude due to orbital eccentricity. This will lead to extreme seasons, unless the planet can store energy and amortize the cycle somehow (like oceans storing energy on earth, but you'll need that on another scale ; or a full greenhouse venus-like system).

1 which is probably unstable : two planets orbiting on each other's L3 point is not a stable configuration.

They're Milankovitch Cycles there are four of them that combine to effect the long-term climate of Earth you won't get that much change just by altering only one of them. The seasons themselves can't be affected on a year-by-year basis by cycles that are short term only on a geologic timescale. Planet A isn't going to have anything in common with the Earth in a highly eccentric orbit, it really isn't going to be anything like Earth if it's in a binary system, in fact it's going to have to be so far from those stars it'll freeze solid. That's not a possible star system anyway, the stars can orbit a mutual centre of gravity or one can orbit the other, they cannot "orbit each other".

The 27 degree tilt is going to create more extreme seasonal variance, summer will be hotter, winter colder, spring and autumn shorter, from memory the difference is about twice the change in tilt, as a percentage, roughly. If you put the two worlds next to each other and looked at them on extreme timelapse, assuming that Obliquity (change in axial tilt) is the only cycle that has a relative difference, you will see a rather different rhythm to the advance and retreat of continental ice sheets what the difference will be is anyone's guess given how little we really understand climate.

For the sake of interest the Milankovitch Cycles are Obliquity, the variation in degree of axial tilt, Eccentricity, the degree to which the orbit deviates from circular, Longitude of Perihelion, where in the cycle of seasons our closest approach to the sun falls, and Axial Procession, where in our orbit compared to Perihelion the summer and winter actually falls, due to the "direction" the rotational axis is pointing. These cycles combine to give Earth an ice-age periodicity of about 100,000 years due to the constructive and destructive interference of the variations in insolation and insolation distribution that the cycles each create. This is also effected by land distribution to some degree as land bound ice is very important to net insolation uptake on a planet.

I would think an M class planet in the habitable zone of its solar system, with a wobbly axis as it spins would do one of two things.

1. It would increase the speed at which the seasons change, so you would go from spring to summer, in one day, then autumn to winter in one night, and so on. 2. It would double the number of seasons the planet experiences.