I created the following system (including a simulation in universe sandbox which seems stable):

  • Sun-like G-type star with same mass, density, radiation profile, diameter and luminosity as the Sun.

  • Gas giant (from now on referred to as "Primary"): 12 Jupiter masses, semi-major axis: 1 AU, Orbital period 1 Year.

  • Moon: 0.6 Earth masses, semi-major Axis 0.00614 AU, Orbital period 39 Hours.

  • The moon has the same density and material composition as Earth.

  • It's tidally locked.

  • The orbit around the Primary is nearly circular.

  • All the bodies have the same axial tilt as Earth.

I know a constellation like this would naturally not form around a sun-like star, but this is a fictional scenario

I'm attaching a physical map I made of the moon's surface, including the grid and the location closest to the Primary below. I already have the following clues about some of the climate factors that may be at play here:

  • Longer day/night-cycle, probably results in increased pressure during the colder night.
  • Red dot on the map: closest point to the Primary this is likely to be a cold spot, since it's often hidden from the sun once the moon passes the planets shadow.
  • This potential cold spot is likely to have increased pressure, since cold air is heavier than warm air.
  • Increased tidal heating, which could result in volcanic emissions leading to an additional greenhouse effect, but also emit particles that provide minor atmospheric darkening.
  • Increased plate tectonics
  • Ocean tides are more pronounced, at least I assume.
  • Lower Coriolis forces, resulting in lower deviation of ocean currents.
  • Brighter night on the moon's Primary-facing side.

So my question is: Can the information provided here be used to draw a somewhat accurate system of ocean currents and winds? Or is there more info needed?

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  • $\begingroup$ If I am picturing this correctly. the moon will go around the gas giant, putting the hole mone into darkness. Then will come out of shadow giving the red dot area a 1st sunrise in the "east", then as it moves in between the sun and primary a 1st sunset, as it proceeds around it will have a second sunrise in the "west" to only proceed back into the shadow of the primary. It will never have a noon or direct sunlight. Thats alot of night time. Most of its heat may very well come from the primary reflecting solar from its surface. This may help regulate sharp temperature changes. $\endgroup$
    – Gillgamesh
    Commented Apr 25 at 12:38
  • 1
    $\begingroup$ Thank you for the answer. According to my simulation, the Gas Giant has an apparent size/angular diameter of 10 in the sky if you would stand on the moons red dotted-Equatorial Point. And if I play it, the sun would appear to be hidden behind the primary for 50 Earth Minutes each day. With a daytime and a nighttime of 19 hours 30 , the moon would still get 18 hours 40 minutes of at least partial daylight on this particular spot. So i think the dimming effect would be quite minimal actually. I updated my question so you can see the size of the sun and the primary. $\endgroup$ Commented Apr 25 at 15:08

1 Answer 1


Hard SciFi: You got yourself an earth without a moon.

You placed a gas giant inside the astroid belt. That's a NONO. During sun formation, gas giants inside the astroid belt are either sucked into the sun or blown away. As a result, we remove the gas giant from the equitation. Because of that, you are left with an earthlike planet without a moon.

Soft SciFi: Handwave it all.

Throw out the numbers. Make it Soft SciFi and handwave everything to get your habitable moon at a long distance. Explain the goldilocks zone around the gas giant far away with the gas giant making heat and ignore normal physics calculation. Just set an average temperature and design your planet from there.

  • $\begingroup$ If I want to discuss these fictional scenarios, which tags should I use? Or should we move this question to another forum? $\endgroup$ Commented Apr 26 at 6:28
  • $\begingroup$ My goal is not to copy earth or our solar system. The goal is to have a habitable moon. That's where my entire work is based on. We have Pandora in Avatar for example. Maybe it doesn't exist in real life, but it works from a cinematic/story standpoint. $\endgroup$ Commented Apr 26 at 6:31
  • $\begingroup$ habitable moons are in theory possibible around rock planets inside the habitable zone, or if the gas giant far out of the goldilocks zone provides heat and does not turn the planet into an irradiated wasteland. You can do it for your story, but you can't expect science to hold up. If you do it, you are writing soft science fiction, where you handwave the whole planetary setup part. $\endgroup$
    – Trish
    Commented Apr 26 at 6:41
  • $\begingroup$ Thank you for the reply. With "in theory possible" do you mean it's possible to form , or do you mean its possible to exist? $\endgroup$ Commented Apr 26 at 6:45
  • $\begingroup$ According to hill sphere and orbital calculations it can clearly be and remain stable. $\endgroup$ Commented Apr 26 at 6:46

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