Thread: Research/Hypothetical Scenario (Extrasolar/fictional planet)

Hello, I am a new member. I came here via a search trying to research for a piece of fiction I am attempting to write. However, now I just wish to pose this as a hypothetical problem. I have no idea if this is the right section of the forum for this, but I am guessing extra-solar planet research is as close a fit to the idea as anything else.

The idea was, with all variables open to adjustment, could there be a planet with noticeable seasons yet no axial tilt? For the fictional planet, I wanted a world with no separate seasonal patterns such as we have in the northern vs southern hemispheres. I also wanted there to be no times, in arctic/antarctic regions, where there are periods where the sun doesn't set or doesn't rise, hence the lack of a tilted axis for the hypothetical planet.

I imagine a planet with an orbit more eccentric than Earth's that allows it to span from one side of it's star's habitable zone to the other. There would also be one moon about the same relative size and distance from the planet as our own. I assume this would work so long as the eccentricity of the orbit does not lead to excessive temperature extremes that would incinerate or freeze life on the planet. While it might not have as well defined seasons as we have, would this still create a cycle of cooler - temperate - hotter - temperate - repeat? Could this even be imagined in such a way to mimic the seasons of one hemisphere of our planet?

Also, with these parameters, what would the effects be that would be different from our own world? I would imagine that with such an eccentric orbit there might be more volcanic activity from the tidal forces of the sun on the planet, such as can be seen on some of Jupiter's moons. But what other differences could be expected?

Any thoughts or impressions would be greatly appreciated. My knowledge of astronomy and geology consists of a single introductory college course each.

Thank you in advance to anyone who offers any ideas or commentary.

In fact, from studies of extrasolar planets, it appears that strongly elliptical orbits are the norm, and our system's almost circular orbits are the exception. An elliptical orbit will generate seasons without axial tilt. The problem is that most such orbits are too damn elliptical, creating massive temperature fluctuations over the course of a year, and meaning it is inimical to life. Of course, a hypothetical planet can have whatever degree of ellipticity in its orbit that you decide.

A planet that is close to its parent star could be tidal locked, so that the same side always faces the star. If the star is a red dwarf, then the temperature may still be in the liquid water region. The light will be redder than ours, of course.


Off the topic, did you know that red dwarf stars may 'live' far longer than almost any other kind, and may still glow enough in a trillion years to maintain life on a close orbiting planet? Our own star is projected to go Red Giant in 500 million years, making life on Earth impossible.

Originally Posted by Neraluz

The idea was, with all variables open to adjustment, could there be a planet with noticeable seasons yet no axial tilt? For the fictional planet, I wanted a world with no separate seasonal patterns such as we have in the northern vs southern hemispheres. I also wanted there to be no times, in arctic/antarctic regions, where there are periods where the sun doesn't set or doesn't rise, hence the lack of a tilted axis for the hypothetical planet.

Its not impossible, but you would need a set of exceedingly stringent conditions to pull it off. For one, I'm not sure if it is possible for a planet to have no axial tilt and still be stable. Every planetary body in our own solar system has an axial tilt, and depending on what is orbiting it, they aren't particularly stable. The tilt of our own planet oscillates every 41,000 years, but that is only because we have a large moon to stabilize it. By contrast, the orbital tilt of our nearest neighbor Mars varies dramatically.

To pull it off, you have to have a very special moon (or multiple ones), which has just the right attributes (i.e. mass, orbit, distance, etc.). Otherwise the axial tilt will change and vary with time.


As for the other stuff, unless you want to try really hard to give the planet seasons, there really isn't any need to give it an eccentric orbit. In fact, an eccentric orbit would probably be detrimental to life living on it. Even if it was only a little bit eccentric, there would probably be long periods of time from one climate extreme to another, and not so much seasons. However I don't suppose it is impossible for some sort of life to live under such conditions, provided that it never leaves the habitable zone of its parent star, so if you want to give your planet an interesting climate, then go for it.

Otherwise, what you can expect is for the different latitudes to have essentially the same weather and climate year round. And if you choose to give it "seasons", the entire planet would experience "summer" and "winter" at the same time.

While it might not have as well defined seasons as we have, would this still create a cycle of cooler - temperate - hotter - temperate - repeat? Could this even be imagined in such a way to mimic the seasons of one hemisphere of our planet?

It would be something like that. However, the "summer" would definitely be shorter than the "winter", since the planet's orbit will swing by the perigee more quickly.

Also, with these parameters, what would the effects be that would be different from our own world? I would imagine that with such an eccentric orbit there might be more volcanic activity from the tidal forces of the sun on the planet, such as can be seen on some of Jupiter's moons.

Not really, unless the eccentricity of its orbit was really large. But I don't think you don't want that to happen, particularly if you want it to be habitable. What causes volcanic activity on Io (Jupiter's moon) is the fact that it is being gravitationally influenced by not only Jupiter, but also the other Galilean moons. But if you want a lot of volcanic activity, you could have this hypothetical planet being stabilized by a large few moons. Just take care not to turn it into Io though.