Celestia Forums

I have an Earth-like moon around a gas giant. Celestia reads that the temperature around the gas giant is aronud 215 K, and around the moon is an even cooler 202 K. According to Celestia, the temperature around Earth is about 260 K - and even Mars is 221 and still relatively frigid.

I want living on this moon to be very similar to living on Earth. And of course, with temperatures that low, I doubt that would be possible without something drastic being different, like a much thicker atmosphere, or a great deal of volcanic activity.

This is a fictional solar system with not much bearing on any particular concept, so I could of course just move the host planet in a couple of AU, but unfortunately there are already planets in that area.

So I'm asking two questions. One - the planet's about 2/3 the size of Saturn. I'm wondering how far the planet would have to be away to not perturb the orbit of another planet. Secondly, if scooting the planet closer in doesn't help, is there any planetary mechanism I can set in that would keep the moon warmer?

For the sake of not being vague: the nearest planet from this gas giant is 4.4 AU away on its closest approach, while the gas giant is 13.7 AU away from the host star.

Thanks in advance.

Angry Space Goat,
If you want there to life on that moon than you are most certainly going to have to move the parent gas giant into the stars habitable zone. I have been working on a mega add-on with the same things in mind. But I approached from the other direction. I looked for a star that we now had a large gas giant in a stable orbit in its parent stars habitable zone. I then worked from there. As far as the other planet goes, I would try to keep your system in the Copernican layout. That is base your system on the layout of our solar system as a model. You can of course adjust the distances some. But do not try and bunch all the planet to close to there star. I am not saying that you have to keep the planet size the same but try and keep them in as similar position as possible. And of course no real erratic orbits or you can kiss any of those moons farewell.

If you are interested I could give you the .scc file for my add-on and you can then plug-in everything else. It would be a staring point.

Don. Edwards

If you've got a planet at ~215K at 13.7 AU, you've got yourself a very luminous central star, which means either a high-mass main sequence dwarf, in which case your system is going to be so young that it is probably not out of its heavy bombardment stage, or a giant star of some kind, around which any Earthlike world would be in the "recently thawed from iceball" stage, which would require some kind of extreme terraforming, but then you might as well install some kind of focusing device (mirrors or something) to increase the temperature anyway if your world is on the cold side.

Gamma Cephei b is one gas giant which could conceivably have an Earth-like satellite; Ursa Majoris 47 b is another.

However these large planets probably have powrful magnetic fields, so any Earth-like moon would need to be at least as distant as Callisto or Titan from the planet, or have a powerful magnetosphere of its own.

Celestia wrote:TET1 Tau
Abs mag: 0.41
Luminosity: 58.4x Sun
Class: G7III
Surface temp: 5,070 K
Radius: 11.19 Rsun

Sol
Abs mag: 4.83
Class: G2V
Surface temp: 5,860 K

For comparison. There wouldn't be problem using Theta Taurus, would there?

Secondly, if I'm moving the world closer to its parent star, how far would be safe that it wouldn't gravitationally perturb the other world in orbit? Jupiter is around 4.4 AU on its closer approaches, if I'm right, so that's what I was aiming for to be safe. How much farther could I move it in without trouble?

Thanks for the help.

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Hill radius

It's the distance within which an object's gravity dominates the orbits of nearby bodies. Outside that distance, the gravitational effects of other objects (like the sun) dominate.

That'll at least give you a place to start.

Angry Space Goat wrote:

Celestia wrote:TET1 Tau
Abs mag: 0.41
Luminosity: 58.4x Sun
Class: G7III
Surface temp: 5,070 K
Radius: 11.19 Rsun

Sol
Abs mag: 4.83
Class: G2V
Surface temp: 5,860 K

For comparison. There wouldn't be problem using Theta Taurus, would there?

The spectrum of Theta1 Tauri is G7III, the luminosity code of III means the star is a giant. As far as I am aware you need a star of type A or above during the main-sequence phase to get a G-type giant, which means a maximum system age of about a billion years - lots of gigantic impact events occurring then.

So there's very low probability that a stable planetary system could have formed around this star?

Define "stable".

Light pressure probably will have quickly pushed away the protoplanetary cloud, but that probably wouldn't prevent planets from forming in all such systems.

Let's just say that whatever planets there are in the system probably have *lots* of craters on them!

Massive star is short life.
During forming planets, or on forming planets, the star will die.
So it is difficult for lives to develop...( ' (Y)')

So what types of stars would be able to support 'stable' systems, similar to our own?

I think it would be dwarves of main sequence, like Sol or Rigel Kentaurus B (G or K type V)... M dwarves are to cold, and the habitable zone is too near the star... Maybe A or F stars type V like Sirius or Procyon could be another good possibility, but I'm not sure...

I think....

Giant stars(I-III) are dying stars. O, B and A type stars are too massive to live long enough time. M type stars are extremely dim and most of them exhibit fatal flare. In the result, F, G and K main sequence(V) and subgiants(IV) may host stable system.
Of course companion stars makes planet's orbit unstable.

In addition, a scientist says that mass of protoplanetary disk is important.
If the disk is massive, more gas giant planets are generated. Massive gas giants destroy their highly circular orbits by stronger gravity. Evenntually, there remain Eccentric planets. Habitable planets in such "massive systems" must ruined by the disaster.

Some M class dwarfs have found their way on to the Tarter and Turnbull Habcat
http://www.nasa.gov/vision/universe/new ... Stars.html
including this one, which I place a planet around;

http://www.orionsarm.com/worlds/Dante.html

Umeboshi wrote:I think....

Giant stars(I-III) are dying stars. O, B and A type stars are too massive to live long enough time. M type stars are extremely dim and most of them exhibit fatal flare. In the result, F, G and K main sequence(V) and subgiants(IV) may host stable system.
Of course companion stars makes planet's orbit unstable.

On celestia, I currently have a inhabited (native humanoid race) planet orbiting an A star. if it's to short a time for a planet to form and get life before the A star (in this case, Deneb) died, what about captured planets?

Just think, if, at the a-star's birth, it captured a frozen planet that already had all the ingredients for intelligent life (and already had primitive bacterias) and warmed it up, could there possibly be at least enough time for an intelligent race to evolve and get out just in time as the A-star dies out?

PlutonianEmpire,

Deneb is an A2Iae supergiant, which means that it is already evolved. Considering stellar evolution calculations one can evaluate that it was an early B-type star of about 15 solar masses before it became the supergiant. Early B-type stars have a typical life time of 10 Million years, this would be much to short, even for your your recaptured planet, to have intelligent life evolved from bacteria.

Caro wrote:PlutonianEmpire,

Deneb is an A2Iae supergiant, which means that it is already evolved. Considering stellar evolution calculations one can evaluate that it was an early B-type star of about 15 solar masses before it became the supergiant. Early B-type stars have a typical life time of 10 Million years, this would be much to short, even for your your recaptured planet, to have intelligent life evolved from bacteria.

So, the only way Deneb CAN have civilization is if it captured a sunlike star that was at least 2 billion years old, right?

PlutonianEmpire wrote:So, the only way Deneb CAN have civilization is if it captured a sunlike star that was at least 2 billion years old, right?

Well, I do not want to calculate the probability for this...

Caro wrote:

PlutonianEmpire wrote:So, the only way Deneb CAN have civilization is if it captured a sunlike star that was at least 2 billion years old, right?

Well, I do not want to calculate the probability for this...

Eh?

Even if Deneb were to have captured an entire planetary system - around a G- or M-class star without disturbing it too much gravitationally, the rather large amount of UV-radiation and the - undoubtedly - fierce weather (stellar wind) from Deneb would probably have a noticible influence on life on a planet in the captured sstem.