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If a planet had two suns...

by baobeiiiii
Tags: planet, suns
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mfb
#19
Nov30-12, 09:55 AM
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P: 11,906
α Centauri B has one known exoplanet, and that is not in the habitable zone.

Letīs call a planet there as Bc.
Do you have any reason to expect such a planet? In addition, how would its orbit look like?

Then the distance between Bc and A goes down to 10,5 AU.
Depends on the 3-dimensional orientation of the orbits.
snorkack
#20
Dec1-12, 01:53 PM
P: 386
Quote Quote by mfb View Post
α Centauri B has one known exoplanet, and that is not in the habitable zone.


Do you have any reason to expect such a planet?
No specific reason to expect exactly this to exist.

On the other hand, γ Cephei B approaches about as close to A as does α Centauri A to B, and γ Cephei Ab manages to orbit unperturbed as far away as 2 AU. Thus, there is no specific reason for α Centauri B habitable zone to be empty.

Quote Quote by mfb View Post
In addition, how would its orbit look like?
Relative ordinary low eccentricity orbit around α Centauri B with minor perturbations from A (presumably precession of the nodes and apsides).
Quote Quote by mfb View Post
Depends on the 3-dimensional orientation of the orbits.
Probably at a low inclination to the AB orbital plane. High inclination would be more vulnerable to perturbations.
Whovian
#21
Dec1-12, 04:23 PM
P: 643
Quote Quote by ImaLooser View Post
The coolest case would be where it orbits the suns in a figure-8 pattern. There would be great extremes of temperature. The orbit would be chaotic. You could have the inhabitants advanced enough to have some sort of control over the orbit, since a chaotic orbit can be influenced by very small changes. Then the orbit of the planet would be a big political issue. Some beings would have evolved to favor one star or the other, so there would be a huge debate.
:D That would be interesting.

Quote Quote by the_emi_guy
Why not choose Sirius as your binary star.
Unfortunately, Sirius B doesn't seem to be too bright, so it wouldn't have much of an effect.

Now, even more interesting would be a trinary star system. (Or even quaternary.) That would allow for some pretty bizarre life. From an earthling's point of view, I mean.
mfb
#22
Dec2-12, 07:44 AM
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P: 11,906
Quote Quote by snorkack View Post
On the other hand, γ Cephei B approaches about as close to A as does α Centauri A to B
There is a factor of 2 between the semi-major axes, and the closest approach corresponds to a higher velocity -> short time there.

and γ Cephei Ab manages to orbit unperturbed as far away as 2 AU.
ε=0.115
Roughly circular, but more eccentric than any planet in our solar system apart from mercury.

In addition, it is the only known system with those properties, indicating that those planets could be quite rare. Possible, but rare - even more if you want to decrease the semi-major axis by a factor of 2.
snorkack
#23
Dec2-12, 11:55 AM
P: 386
Errai AB semimajor axis - 20,2 AU
eccentricity 0,41
period 67,5 years

Toliman AB semimajor axis - 23,4 AU
eccentricity 0,51
period 79,9 years.
mfb
#24
Dec2-12, 12:37 PM
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P: 11,906
Oh, I misinterpreted your previous post:
Quote Quote by snorkack View Post
The smallest distance between B and A is 11,2 AU at periastron. Then the distance between Bc and A goes down to 10,5 AU.
Ok, the stellar orbits are similar.

Gamma Cephei A (with planet) has 1.4 solar masses, Gamma Cephei B has 0.4 solar masses. The companion has less mass and less gravitational influence.

Alpha Centauri B (with planet) has 0.9 solar masses, Alpha Centauri A has 1.1 solar masses.
The companion has more mass.
The relative ratios differ by a factor of 4,6.
dodo
#25
Dec2-12, 06:17 PM
P: 688
If you allow me the license, I thought I would add a marginally off-topic post; perhaps still useful if comparisons to Earth are intended. It involves changes to our own solar system, rather than planets formed from scratch in a binary system, so admittedly not the same.

I was rewatching the movie "2010" recently, which ends (I assume this is no spoiler by now) with Jupiter becoming a second sun. I am no physicist myself, but perhaps many of the other posters may confirm my Wikipedia speculation that this would certainly be no paradise for us.

First, if we are worrying about global warming, now imagine adding a second sun sourcing heat to the planet. But this is not really the worst.

For Jupiter to emit visible light, it would have to increase its mass at least 70-80 times (fusion of elements other than hydrogen may start to occur at a smaller mass, but these would only make it glow in the infrared, like what we know as "brown dwarf" stars; for a shiny second sun you really need to fuse hydrogen). But, as the mass of Jupiter increases that much, it will also start falling towards the sun. Guess who is in the middle. At the very least, a large asteroid belt is. So now you have sort of a kitchen blender splashing rocks at the outskirts of your planetary system. But this is not still the worst.

As Jupiter normally orbits the sun, its present mass makes the sun "wobble" - but not by much: just about as much as the sun's radius, but not really much more. A Jupiter that is 70-80 more massive would make the wobbling extremely close to the orbit of Mercury, at least at Jupiter's current distance (granted, less so as Jupiter starts falling in). Now Mercury gets into a violent eccentric orbit; it may or may not fall into the sun, but it may eventually get fractured in pieces by the violence of its new orbit. So now you have another splashing blender in the middle. But this is not yet the worst.

The rest of the inner planets, Venus, Earth and Mars, will likely leave their almost-circular orbits acquired after billions of years of relative quietness. So now, instead of some dozen degrees of temperature difference per year, your planet (assuming it doesn't smash into something, which it eventually will) may likely have a couple hundred degrees of difference between summer and winter. During the summer, lava will run the surface and stones will melt; in the winter, you will be breathing liquid nitrogen instead of air. Bad for your health.

As said, not the same as the OP's request. But the post was intended to illustrate how relatively peaceful, boringly circular our neighborhood is. And how very different life may have to be (perhaps even subterranean, away from the surface; perhaps without an atmosphere at all) in order to survive planets in eccentric orbits, subject to violent tidal forces and temperature extremes.
mfb
#26
Dec3-12, 07:38 AM
Mentor
P: 11,906
I think the movie did not mention any increase in the Jupiter mass - the object somehow catalyzed fusion (?).
A significant larger Jupiter mass would scatter objects in the asteroid belt all over the solar system - even if our orbit stays reasonable, this would be a serious threat.
snorkack
#27
Dec3-12, 11:49 AM
P: 386
On the limit of extremely massive perturbing body, Moon is perfectly stable long term and has a modest eccentricity although it completes only 13 7/19 orbits in one orbit of te perturbing body. And around Jupiter, S/2003 J 2 has a period almost one quarter that of the perturbing body.
aerrowknows
#28
Dec3-12, 10:01 PM
P: 4
As was said earlier, there are many possible permutations and outcomes depending on the exact orbital size and mass of the planets. One possible permutation that was not brought up is that the planet will orbit around both stars as they orbit each other.

To understand this, imagine the figure 8 or infinity sign if you will. The planet will orbit in this shape with 2 suns at the focii of the figure ( means the two suns would be in 2 spaces in the figure ).

The implications would be that the planet experences 9 distinct seasons: 4 around one star, 4 around the other star, and one in between the two. The one in between will have the condiition of constant sunlight for that season since the sun shines from both directions. The 4 seasons per star are governed by the distance,size and temperature of that particular star. For example , a winter around 1 and a very cold winter around the other.
ImaLooser
#29
Dec4-12, 04:24 AM
P: 570
Quote Quote by Dodo View Post
I

But, as the mass of Jupiter increases that much, it will also start falling towards the sun.
Not so. Masses and densities have nothing to do with orbits. What really matters is angular velocity. If the extra mass changed angular velocity then the orbit would become elliptical.

It is true that randomly adding 80 Jupiter masses to the Solar System would have a major effect on its stability.

I bet Clarke added a Baim Capital Fu-Zo-Matic to catalyze fusion. I don't know whether that is possible.
ImaLooser
#30
Dec4-12, 04:27 AM
P: 570
Quote Quote by aerrowknows View Post
One possible permutation that was not brought up is that the planet will orbit around both stars as they orbit each other.
.
Hah! Beat you to it. I think that that is the most interesting scenario. There would be temperature extremes so human life seems impractical, you can have fun inventing some other forms.


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