# Science fiction story

Hi, everybody :)
I joined this forum because I'm currently writing a sci-fi story and I want to create an alien world that is scientifically correct, but due to my lack of knowledge and experience I'm facing some big troubles. I have a ton of questions(I hope I won't bother you much).
So here is short description of my plot: there is an icy moon orbiting around a gas giant around 20% bigger than neptune. The moon itself is almost the size of the earth has almost the same atmosphere as earth, and these bodies are all part of a P-Type binary star system with one big yellow dwarf(like our sun) and the second star is orange dwarf 16% smaller than the main star, both stars are around 0.2AU from each other. The gas giant is 2.5AU far away from the both stars. I suppose all objects on the icy moon would cast two shadows, but I have no Idea how exactly they should look like during the different times of the day(sunset, noon...) would they be fuzzy on the dawn and sharp clear at afternoon? Please give me as detailed description as possible, I tried to render a scene on Maya with two lights and one solid object, but I can't make good render output because I'm touching maya for the very first time...
Thank you in advance.

## Answers and Replies

Related Writing and World Building News on Phys.org
I suppose all objects on the icy moon would cast two shadows, but I have no Idea how exactly they should look like during the different times of the day(sunset, noon...) would they be fuzzy on the dawn and sharp clear at afternoon?
2 shadows that mostly overlap.

However, the change would not be based on the day on your exomoon. Your stars would encircle common centre of mass in something like a month. During such cycle, for an observer, they would 2 times eclipse each other and 2 times spread apart. During eclipse and near it you have one shadow, otherwise two.

Concerning day on your exoplanet. You know, that you are supposed to have rather long one, right?

Ogi
Thank you for the answer.

Concerning day on your exoplanet. You know, that you are supposed to have rather long one, right?
Yes I'm aware of that, I suppose when the two suns are eclipsing then the day and night would be equal, now I'm trying to construct a binary solar system with MAYA to get better picture of the phases, rotations and other motions in the system...

Also my plot places the characters in the outer space far away from our local galactic group, some kind of cataclysm sends our guys
in more than 200 million light years away from earth, in the alien binary solar system we were talking about, so I was wondering is it possible for the scientists to find out where exactly are they in the universe, where is Earth, or milky way. Their ships have all kind of astro equipment - radio telescopes, optical telescopes, cosmic background radiation observatories and so on...

Concerning day on your exoplanet. You know, that you are supposed to have rather long one, right?
Um, why?
So here is short description of my plot: there is an icy moon orbiting around a gas giant around 20% bigger than neptune.
In which measurement?
The moon itself is almost the size of the earth has almost the same atmosphere as earth, and these bodies are all part of a P-Type binary star system with one big yellow dwarf(like our sun) and the second star is orange dwarf 16% smaller than the main star,
In which measurement?
both stars are around 0.2AU from each other. The gas giant is 2.5AU far away from the both stars. I suppose all objects on the icy moon would cast two shadows, but I have no Idea how exactly they should look like during the different times of the day(sunset, noon...) would they be fuzzy on the dawn and sharp clear at afternoon?
Yes, because of Earth-like atmosphere.
The angular distance between stars never reaches 5 degrees. Moon can pass Sun farther than that.

Thank you for the answer.

Yes I'm aware of that, I suppose when the two suns are eclipsing then the day and night would be equal, now I'm trying to construct a binary solar system with MAYA to get better picture of the phases, rotations and other motions in the system...
I mean long day because of tidal locking:
https://en.wikipedia.org/wiki/Tidal_locking

Also my plot places the characters in the outer space far away from our local galactic group, some kind of cataclysm sends our guys
in more than 200 million light years away from earth, in the alien binary solar system we were talking about, so I was wondering is it possible for the scientists to find out where exactly are they in the universe, where is Earth, or milky way. Their ships have all kind of astro equipment - radio telescopes, optical telescopes, cosmic background radiation observatories and so on...
Seems plausible. At this moment we know that we're within Laniakea Supercluster, which spans for 520 million LY. So from 200 mln LY from our star seem in theory not as problem, to estimate our position:
https://en.wikipedia.org/wiki/Laniakea_Supercluster

In practice it assumes that ship has a good back up of data concerning far galaxies. And also some calculations, the especially tricky ones would include this time lag... after all we would see our galaxy as it was 200 mln, when Earth was in Triassic era ;)

almost the same atmosphere as earth
Do you know, that you have here some leeway?

Ogi
Concerning day on your exoplanet. You know, that you are supposed to have rather long one, right?
Um, why?
Tidal lock. So one day - one orbit around the planet.

Sure, he can put it on a low orbit, but already Io with its 42h day has got terrible volcanism, and he is requesting a habitable planet.

Sure, he can put it on a low orbit, but already Io with its 42h day has got terrible volcanism, and he is requesting a habitable planet.
Io has volcanism because it has eccentric orbit because of perturbations from Europa that just happens to be in a disturbing resonance.
Look at Mimas. 23 hour day and no volcanism.

Io has volcanism because it has eccentric orbit because of perturbations from Europa that just happens to be in a disturbing resonance.
Look at Mimas. 23 hour day and no volcanism.
Do you think that those two suns would not bring any perturbations? ;)

And Mimas has radius of less than 200 km, Io has radius of 1821 km, and he needs even more for Earth like moon. There would be more nice ratio of mass to surface through which those tidal heat could leave.

If you prefer Saturn moons, what about selecting something bigger... like Titan with its presumed cryovolcanoes...

Last edited:
Do you think that those two suns would not bring any perturbations? ;)
By my estimate, their orbital period relative to each other is in the region of 24 days. If the moon is on a low orbit, there would be little chance of resonance.

Also my plot places the characters in the outer space far away from our local galactic group, some kind of cataclysm sends our guys
in more than 200 million light years away from earth, in the alien binary solar system we were talking about, so I was wondering is it possible for the scientists to find out where exactly are they in the universe, where is Earth, or milky way. Their ships have all kind of astro equipment - radio telescopes, optical telescopes, cosmic background radiation observatories and so on...
Given that your guys have a large database, and all manner of telescopes etc, I they should I think be able to find matches for a few objects that have unique signatures.
Only 3 or 4 definite matches would enough for them to get some idea of their location.
This would be complicated though by the fact that things can change a lot in 200 million years/
(Yes I know that light years is a measure of distance, but that amount of displacement would result in objects being observed at a different point in their history)
Possibly things like quasars would remain identifiable.

Drakkith
Staff Emeritus
Science Advisor
Also my plot places the characters in the outer space far away from our local galactic group, some kind of cataclysm sends our guys
in more than 200 million light years away from earth, in the alien binary solar system we were talking about, so I was wondering is it possible for the scientists to find out where exactly are they in the universe, where is Earth, or milky way. Their ships have all kind of astro equipment - radio telescopes, optical telescopes, cosmic background radiation observatories and so on...
Absolutely. They should be able to find out where they are by looking at distant galaxies and comparing them to previous observations. For a change of 200 million light years they should see some fairly obvious parallax, size differences, and changes in the apparent shape of known galaxies since they are viewing them from different angles and distances than before. There may even be enough change in the redshift of galaxies to measure as well.

At minimum they should be able to look around and spot a galaxy cluster whose mass and distribution matches what we already know about the local group.

I mean long day because of tidal locking:
In my story the moon will not be tidally locked, is this it possible for such a large satellite? Also the moon will be rotating clockwise both around the gas giant and it's axis.

In which measurement?
Equatorial radius - is this a good example when we want to describe the size of a planet?

Io has volcanism because it has eccentric orbit because of perturbations from Europa that just happens to be in a disturbing resonance.
Look at Mimas. 23 hour day and no volcanism.
Yes the satellite seismology should be something like Mimas, but the gas giant has 6 more moons, one of them the second largest moon(the frozen one we were talking about is the largest moon)is with the size of Saturn's Titan, would this cause a violent volcanism on the frozen moon?

And finally I want our guys to be lost in the space, even though they have very sophisticated instruments and telescopes, Is there a chance for them to have no idea where they are, and how that should be described?

Last edited:
In my story the moon will not be tidally locked, is this it possible for such a large satellite? Also the moon will be rotating clockwise both around the gas giant and it's axis.
Any big close satellite would become quickly tidally locked, the only way is to put it on far away orbit.

Equatorial radius - is this a good example when we want to describe the size of a planet?
Mass would be more practical. For simplicity sake I'd assume 1.73 mass of Neptune (we're both ignoring higher compression and higher temperature of the gas, let it be)

Using formula:
https://en.wikipedia.org/wiki/Tidal_locking
And assuming that this moon would be 20900000 km away:
https://en.wikipedia.org/wiki/Ferdinand_(moon)

Seems - OK.

[playing a bit more with formula]

Just keep not much closer than 3 mln km (almost ten times our distance to the Moon). One orbit around the planet - at least 117 days.

Ogi
Thank you all for the detailed information :) I hope I'll be able to create a scientifically accurate environment.

Drakkith
Staff Emeritus
Science Advisor
Just remember that characters, conflict, and plot are all more important for fiction than accurate science. Though the latter can be used to enhance the former.

Ogi
As for finding a way home or knowing your position in the galaxy: I would use pulsars. Pulsars don't change much through the eons, and they have a very precise frequency which will be unique. They're also big enough that you could likely detect them from a very long ways away. When we sent out the Voyager probes, we used the distance to 13 pulsars and their frequency to give any alien life a map back to our location.

Ogi
This technique with the pulsars is very interesting, never heard about it before, thank you :)

DHF
You said you want your characters to have no idea where they are. However I think knowing where they are is important otherwise why decide that they are 200 million light years away? Knowing where you are and knowing how to get home are two very different things.

If your intrepid heroes are at our current level of technology then its also possible to have an idea of where you are but knowing exactly where they are might be impossible. At those distances, even if they knew where they were with 90% accuracy...that leaves a margin of error worth millions of light years.