Information and Context

I'm working on a story, based 220 or so years in the future in a hard-science universe (where a quantum jump drive has been invented). I was wondering if anyone could give me some information and advice.

This is also my first time doing any project like this.

I plugged some information into this calculator.
Plugged in values:

  • Day length: 120 (I want it to be really long)
  • Mass: 0.4 (I want less gravity)
  • Radius: 0.7 ( ^^ )

Output values:

  • Density: 1.16618
    • Minimum Density: 2 g/cm3
    • Typical Density: 5.2 g/cm3
    • Maximum Density: 11.1 g/cm3
    • Actual Density: 6.437 g/cm3
  • Radius: 8920 km
  • Surface Area: 249.9 million km2
  • Roche Limit: 1200 km
  • Surface Gravity: 0.82 Gs
  • To Orbit Velocity: 5.99 km/s
    • Thrust Time to Orbit at 3 Gs: 4.9 minutes
  • Escape Velocity: 8.5 km/s

If that's too much information, or not enough, please say so.

For plot reasons, It would be nice if the days and nights were really long. Also, I'd like the planet to be a bit darker / cooler than earth, but still be bright enough to easily see (for humans) on the surface.


  1. What could the planet's sun / orbits look like?
  2. How long is viable for a day / night cycle with that sun / orbital system?

If you have any general tips, or ideas, or links to share, please do! Any help is appreciated!

Thanks to all those who gave me advice as I am very new to this!!

  • 3
    $\begingroup$ Wow this is a lot of stuff! Just to warn you, you might get some 'too broad' close votes, since it's usually encouraged not to ask more than one question per post. I recommend maybe asking some of these separately, and also looking around on the site to see if there's anything useful. Best of luck! $\endgroup$ Oct 19, 2017 at 1:24
  • 1
    $\begingroup$ Please, one question per, ummm, question. $\endgroup$
    – Mołot
    Oct 19, 2017 at 3:47
  • 1
    $\begingroup$ Yes this is rather a lot to ask in one go - can you restrict it to 1 or at most 2-3 closely interrelated questions $\endgroup$
    – Slarty
    Oct 19, 2017 at 4:10
  • 2
    $\begingroup$ "A quantum jump drive" doesn't sound as particularly belonging to hard-science to me... $\endgroup$
    – AngelPray
    Oct 19, 2017 at 20:32
  • 1
    $\begingroup$ Interesting question, welcome to WorldBuilding. I'd recommend taking a look at our already existing questions, you might find some of them interesting. For example to use the search box in the upper right: [planets] long day is:q will search for all questions tagged planets that contain the words "long" and "day" yielding stuff like Realistic sky of an Earth-like moon orbiting a gas giant (length of day and size of celestial bodies) $\endgroup$
    – Secespitus
    Oct 19, 2017 at 20:36

1 Answer 1


In answer to the Day/ Night cycle, There is no real physics based reason you can't just say the day is however long you want it to be.

In terms of what an orbit looks like, taking a bit of a look at what goes on in Mars should demonstrate for you that what you want is supported by Hard Science fairly easily. A somewhat eccentric orbit will give you seasonal variations to your hearts content

Here is a picture of Mars Orbit: enter image description here

This came from a page that describes quite a bit about what goes on in Mars that is similar to what you are trying to do: https://www.universetoday.com/14717/how-long-is-a-day-on-mars/


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