
Amateur astronomers discover a planet with four suns - boh
http://io9.com/5951865/unprecedented-amateur-astronomers-discover-a-planet-with-four-suns?utm_source=lifehacker.com&utm_medium=recirculation&utm_campaign=recirculation
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InclinedPlane
I tracked down the original paper (<http://arxiv.org/abs/1210.3612>) and dug
up some useful details.

The planet in question is a gas/ice giant similar to Uranus with a radius 6
times that of Earth (nearly 80,000 km in diameter) with an as yet unknown mass
(although it must weigh less than half of Jupiter's mass at the most). It
orbits a pair of binary stars with a period of 138 days. The binary it orbits
is an F dwarf star with 1.5 the Sun's mass and an M dwarf with 40% of the
Sun's mass, they orbit each other with a period of 20 days. For reference,
this translates to the two stars orbiting much closer than Mercury's orbit
(around 0.17 AU) and the planet with an orbit close to that of Venus (around
0.65 AU, according to my calculations).

This system is bound to another binary system of similar total mass (a G2 star
similar in mass to our Sun and an M2 dwarf star with around half or less the
mass of our Sun) at a distance of around 1,000 AU. At that distance the second
binary system would merely be the brightest stars in the night sky of the
planet. The two binary systems would orbit each other with a period of tens of
thousands of years.

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ChuckMcM
I've tried about 8 different ways to modelling that and so far all of them
have the planet being ripped apart as soon as its orbit is elongated by the
traversing between the two pairs of binaries. Bizarre doesn't begin to
describe it.

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InclinedPlane
This doesn't make sense to me. The two pairs of binaries are around 6 _light-
days_ apart. The gravitational forces they have on each other are miniscule,
but they are persistent enough to cause the two systems to orbit each other
with a period longer than the duration of human civilization.

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ChuckMcM
Yes, and if you model the force on the planet when it travels between them it
has a small tidal effect. Depending on the relative orbital planes of the
planet and the second binary star system, that may occur any time from once
per orbital period to once every 10,000 years. But now try to see how the
planet stays in a stable orbit over a billion years. At least in the models
I've been able to come up with the tidal effect is assymetric, which is to say
the tweak to orbit of the planet is not counter acted by a symmetric tweak on
the far side. Even starting with the 'suns' being effectively two point
sources 1000AU apart in a bilaterally stable orbit. Trying to find a way to
reliably orbit a planet around one of them stably is eluding me. If you can
come up with some orbital parameters that work I'd love to see them.

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InclinedPlane
Apologies for my skepticism, my estimate is that the distant binary star
system would impart a force on a planet less than 5% that of Jupiter on Earth.
Could you provide more details on your n-body simulations? Such as what code
base you are using, etc.

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DanBC
They were using Planet Hunters - which appears to be a crowd sourced "find
interesting bits in all this data" website. (<http://planethunters.org/>)

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bdisraeli
I work for the group that made Planet Hunters. We have a variety of similar
projects at <http://zooniverse.org>, including four others we launched in the
last month that have people classifying sea floor life, galaxies, cyclones,
and bat calls.

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DanBC
They're very cool projects! I've been noodling around for a bit.

I'll register if I think I'll be any good, and I'll certainly be passing the
URLs around to people if I think they'll be interested.

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tocomment
Any chance someone could make a diagram of the orbit for us? I really can't
picture this? Does it make a figure 8 around the first two stars?

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InclinedPlane
It's a pair of binary stars with a planet orbiting one pair.

To give you a conceptional model, imagine that Mercury is a star and then
imagine that, say, Saturn and one of its moons are also stars. Now, obviously,
orbital mechanics are going to change when you have all of these much more
massive bodies in the system, but hopefully you get the picture.

Edit: obviously not to scale, but maybe this helps:
<http://i.imgur.com/RJrOw.png>

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jmilloy
Your parent is asking how the planet orbits two stars, and probably how the
2-star-1-planet system orbits the two other stars. That is, "how does any body
orbit two stars?"

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InclinedPlane
And I explained. How does the Earth orbit the Sun-Mercury system? It's no
different than how a planet orbits a binary system from afar. The two stars
orbit each other and then the planet orbits around both stars. And then that
whole system orbits around another binary star system at a tremendous distance
(1,000 AU, ten times farther away than Voyager 2 is from the Earth now).

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fusiongyro
It's a little different; in our solar system, the Sun is one of the foci of
the ellipse, whereas in a binary system that focus would instead be the center
of gravity between the two stars.

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drcube
Although Mercury in this instance is extremely insignificant, technically the
earth orbits the center of gravity of the Sun and Mercury. Actually, the
center of gravity of the Solar system as a whole, but I'm just going along
with the GP.

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fusiongyro
Gosh, how incredibly helpful.

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b_emery
Their link to human vs machine is interesting:

<http://www.planethunters.org/science#human>

I wonder how good their machine learning is? I'd love to throw some support
vector machines or neural networks at this stuff!

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sadga
A team at McGill made a "game" to find patterns in I think protein-folding or
genome data, to leverage humans to identify patterns that their algorithms
could not.

<http://en.wikipedia.org/wiki/Phylo_(video_game)>

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wooptoo
Man, everything has to be quad core these days.

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zandorg
Overheating too, I guess.

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twmb
I wonder if it's a planet such that the surrounding stars' lights prevent any
other starlight from being seen, except for once every few thousand years.

One could only imagine a civilization that lives here and what would happen to
society whenever the full night sky is occasionally seen...

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DougWebb
The planet is a Neptune-like gas giant, so no civilization there. It probably
has big moons though, and with all the suns around they might be warm enough
to develop life. I haven't done the math, but I'm guessing that when the moon
is on the night side of the planet relative to the nearby stars, the location
of the distant stars would cycle in basically the same way Jupiter does in our
sky. It moves slowly relative to the background stars, but still rises and
sets every day.

I don't know the details and couldn't do the math if I did, but I'm guessing
those stars at 1000AU can't be much brighter than our full moon is, maybe
combined with the light pollution of a big city. I've lived outside of New
York all my life, and my night sky still has stars in it. Not many, but enough
to know they're there, and sometimes on a clear night I can see quite a few.

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pdonis
> I'm guessing those stars at 1000AU can't be much brighter than our full moon
> is

They may well be fainter. According to Wikipedia, the Sun is about 400,000
times as bright as the full moon, on average:

<http://en.wikipedia.org/wiki/Apparent_magnitude>

So if the Sun were 1,000 AU away from us instead of 1 AU, it would be a
million times fainter (1,000 squared), or _less_ bright than the full moon.

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SoftwareMaven
But there are two of them, so that would mean closer to the moon's brightness,
right? If I'm following, the sun would be about 40% as bright ast he full moon
at 1000AU, so with the second start being smaller than, it may be 60%?

(Mock my math if need be, I'm not really trying here. :)

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pdonis
Yes, the second star would add to the brightness and make things closer. Also,
I didn't see in the article what the actual brightnesses of the two stars
1,000 AU away are relative to the brightness of the Sun. I just used the Sun
because it was easy to look up the relative brightness of the Sun vs. the
Moon. :-)

Edit: I see from looking at more recent posts that the two distant stars are
thought to be spectral class G and M. The Sun is a G, so it should be about
the same brightness as the brighter of the two.

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pm
Brian Aldiss referenced a similar kind of system in his Helliconia science
fiction trilogy, where a planet orbited a small sun, which in turn orbited a
much larger sun in a much longer orbit.

Ironically, truth turns out to be stranger than fiction, seeing as this two
binary systems are involved.

