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back to article PLANET-SWAP shock: Stars grabbed dirtballs from other clusters

Space boffins have suggested that billions of stars in our galaxy have captured roaming rogue planets as they tootle through the cosmos. Artist's impression of a rogue planet tootling through the universe Artist's impression of a rogue planet tootling through the universe. Credit: Christine Pulliam (CfA) The rogue planets, …

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Trollface

Artist's impression

Artist brings own massive spotlight?

I'm pretty sure rogue planets are black, because they are light years away from any stars.

Disclaimer: Not an astro-boffin

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Re: Artist's impression

Nor me - astro or otherwise, but it never seems to stop me pontificating...

It appears also to have clouds, and frozen polar caps...

It must be near a star, or some source of heat...

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Go

Re: Artist's impression

Such a rogue planet would wander relatively close to a star from time to time. Perhaps it's being illuminated by such a star which is out of frame. Even at a distance of one light year, a star like our Sun would be bright enough to cast shadows. Perhaps the planet depicted is in the process of being captured :)

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Re: Artist's impression

Ok i'll bite, you'd have preferred the artist painted a black sphere against the emptyness of space?

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Re: Artist's impression

Quote: "Even at a distance of one light year, a star like our Sun would be bright enough to cast shadows"

Are you sure about that? Any references?

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Mushroom

Re: Artist's impression

Look, if you want to go take a photograph of something which you know won't be illuminated, you bring a flash. Or two. Or half a dozen. In this case it's probably a dozen thermonuclear devices. And if it's a long journey there, a couple of days extra setting up the lighting so that you'll have the best image possible will be inconsequential.

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Are you sure about that? Any references?

Sure, it's been calculated that at a distance of 1ly the Sun would have a magnitude of about -4 (see http://www.bautforum.com/archive/index.php/t-47706.html and there's various other sources you can Google,) which is about as bright as the planet Venus from Earth. On a very dark night with no street lighting etc, Venus can be seen to cast shadows.

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Re: Are you sure about that? Any references?

In fact there's some working out here: http://www.bautforum.com/showthread.php/36560-1-lightyear-distance-from-the-sun?p=641829#post641829

According to this it's magnitude -2.69, which would be rather brighter than Jupiter and is still bright enough to cast shadows.

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Probably more common

N-body systems (where N >2) tend to be unstable except under certain conditions (lagrange nodes, resonant orbits, one planet WAY far away from two stars). So I expect these "rogue" planets are fairly common, having been kicked out by gravitational dynamics.

And I would nominate Hollywood as a place that originated in an alien system and got kicked out. Especially if that system had taste.

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Cue planetary racism: we do not like your type here, you do not belong here really!

But maybe planets of a certain age have gained wisdom, rather than becoming stupid with more authority (as Lu Tse said in "Thief of Time")

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Ogi
WTF?

How did they spot two worlds orbiting each other without a star?

Forgive my ignorance, but I was under the impression that our telescopes are not powerful enough to see exoplanets on their own. They can only spot them when they pass across their star, or by the effects the planets have on their star (e.g. gravitational).

So we only observe the stars directly, and infer the planets from the star, so how do you spot planets when there is no star to observe and infer from?

Any astroboffins in the ranks who can enlighten me?

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Re: How did they spot two worlds orbiting each other without a star?

If the planets pass between us and any star we're looking at, there's a chance we can see them. Doesn't necessarily have to be their own star, they could just pass in front of us like ET in front of the moon.

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Ogi

Re: How did they spot two worlds orbiting each other without a star?

So basically we got lucky :)

Thanks for the explanation! It does seem obvious in hindsight, lol!

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Anonymous Coward

IANAA

> If they pass a different star later on, which is moving in the same direction and at the same speed

How does this statement make sense?

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Re: IANAA

I read that as rogue planets and stars orbiting the centre of the galaxy. IE the galaxy rotates. But you are right, if both star system and planet are orbiting the galaxy at the same speed how would they join up?

Now I'm comfused...

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Boffin

Re: IANAA

By putting a "roughly" into that sentence.

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Gimp

Beware

Mondas may return !!!!!!!!!!

(icon obviously an early prototype)

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This is a bit of a mish-mash article

I think that what has happened here is that the results from a very specific initial condition have been badly projected in to a general condition.

Just some of the things that bother me about this article:

"...end up trillions of miles away." - one light year is 6.8 trillion miles. However, one light year isn't very far away at all ("Space [the HHGTTG says] is big. Really big. [...] you may think it's a long way down the road to the chemist's but that's just peanuts to space..." D.N.A.). Having said that though, stars in a cluster can be less than one light year apart.

"The clusters then disperse..." - Why should a cluster disperse? The globular clusters around most galaxies appear to be some of the oldest parts of those galaxies, at least judging by the fact that they seem to contain the oldest stars, and they haven't dispersed despite being close to a mucking great gravity well and all the perturbations that implies. Extra-galactic clusters will hardly be perturbed by anything and should be even more stable. One of the notable things about clusters seems to be their stability.

"...pulling once-neighbouring planets away from each other to end up hundreds or thousands of times farther from each other than the Earth is from the Sun." - The Earth is 1 AU from Sol whilst Neptune is ~30 AU from Sol. Eris varies between ~40 to ~100 AU from Sol and the Oort cloud is reckoned to extend out to about ~50,000 AU - roughly one light year, so once again, hundreds or even thousands of times further away than Earth isn't really very far at all.

"If they pass a different star later on, which is moving in the same direction and at the same speed..." - A couple of other folk have already commented about this but to clarify, if the planet and the star are moving in the same direction and at the same speed, and they're close enough for one to capture the other, then they must have come from the same place, at the same time.

Sure, planets can be ejected from their parent systems but they have to pick up a lot of speed to do so and this means it's difficult for another star to capture them.

However, capture can occur if the ejected planet has previously been through sufficient close encounters with enough other stars to slow it and change its path such that it ends up on a relatively slow intersecting course with another star. But this won't be a 'same direction, same speed" path.

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Boffin

Re: This is a bit of a mish-mash article

With regards to the same speed, same direction bit, objects can be roughly travelling in the same direction, at roughly the same speed having come from very different places. For a case in point, consider a planet in orbit around a star, and another, more massive planet, brown dwarf, or second star. This second object can quite happily come trundling through this two body-system and it can do it at the same speed and in the same direction as the planet. Its momentum means that it isn't in orbit around the first star. Consider also the fact that the orbital motions of a system cannot be solved for more than two bodies (in much the same way that the schrodinger equation cannot be solved exactly for more than two particles), and that space contains more than two objects, by quite a margin. Excepting the odd situations where bodies are stabilised by things such as resonant orbits, the motion of everyhing in space is essentially chaotic.

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Re: This is a bit of a mish-mash article

The problem with any body travelling through space, that's moving fast enough to cross between different star systems that are far enough apart for planets to develop and assume stable orbits*, is that they have to be travelling at much higher speeds than orbital velocities to escape their original system. In an encounter with such a passing body, a planetary body orbiting the passed star is quite likely to be thrown out of its orbit, and even possibly thrown out of its parent system in turn, but it's very unlikely for the passing body to capture the orbiting body because of the speed differential.

On the other hand, if the passing body has been slowed by previous encounters, like the one described above, to approach another system relatively slowly then it's going to upset and perturb the system it's approaching well before it gets close enough to capture anything; even another Jupiter sized body passing within a thousand AU or so of our Sol would cause havoc within our system.

I mostly agree though, having coded a multi-body gravity sim, that orbital/gravitational motions for multiple bodies are chaotic, but have a look at Klemperer Rosettes (note that these configurations would be unstable in real life though - any perturbation, however small, would ultimately upset them).

Like I originally said, it's not impossible, but it's very, very unlikely. On the other hand though, in an infinite universe everything must happen.

* In a cluster the stars are much closer together but the resultant perturbations means that planets are very unlikely to form and assume stable orbits.

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Pirate

wow

Interstellar travel at hyperdrive speeds just got much more dangerous. Large, unlit planets lurking in dark pockets, unknown until some boozer plows into them at .9c after a long night at the pub. Definitely need to keep your Interstellar Garmin updated.

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Coat

Ohhhh, so that's where Pluto went.

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Coat

If you see a set of planets

If you happen to see a set of 5 worlds orbiting a 6th in a Klemperer Rosette, it can be worth a lot of cash.

The one with the fat check from General Products in the pocket - I'm a bit forgetful recently for some reason....

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Uranus

Sorry, not another "your anus" joke... but with Uranus' odd vertical rings, wouldn't that be a good choice for a potential rogue planet?

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Re: Uranus

It's not just the rings that are tilted; the entire planet has been toppled 97 deg and it appears to be 'rolling' around its orbit. Most likely reason is that something pretty big hit it but it might also be connected with the speculated migration of the gas giants outwards from earlier orbits much closer to the Sun.

Its low orbital eccentricity and inclination from the solar ecliptic plane suggests that it wasn't captured but slowly spiralled out; a captured body would be likely to have much higher orbital and planar eccentricities, a bit like Pluto or Eris. However, just having relatively high eccentricities doesn't mean that these bodies were probably captured either.

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Non-Zero

"We can rule out large planets," Perets said. "But there's a non-zero chance that a small world might lurk on the fringes of our solar system."

There's a non-zero chance I might wake up with wings tomorrow.... what's wrong with saying there's a very small chance our solar system could have a rouge planet ? Also working out the rough odds can't be that hard and if they work out in the same range as me flying to work in the morning then just say it's very very unlikely !

Picky/petty yes but annoying :p

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Boffin

Re: Non-Zero

What they mean is that a gas giant-type planet would have been spotted by now on account of it being huge (thus occluding stars) and massive (notably affect the orbits of stuff we know about).

Something small, like Earth/Venus or smaller might not have been.

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Re: Non-Zero

"what's wrong with saying there's a very small chance our solar system could have a rouge planet ?"

We already have one: it's called Mars.

"Picky/petty yes but annoying :p" Me too.

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boffins

"boffins" says it all........ so how would our esteemed "boffins" have any idea this might have happened? I mean really; we don't even know what happened in this solar system much less ANY system anywhere....

This is exactly what we have become today: any "boffin" anywhere saying anything they want because they can.

boffin = idiot.

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FAIL

Re: boffins

Let me get this straight - you're asserting that scientists are all idiots. I can only assume that the computer you used to write that message on was designed and built by God?

And boffins are the idiots? You're either a troll, or very stupid yourself.

FWIW, we can deduce a LOT of things about the formation of our own solar system, from the motion and orbits of the planets and their moons, from the isotopic constitution of meteorites, the structure of the Earth (which itself can be deduced from the way waves from earthquakes travel through it), etc. etc. Just because we cannot wind back time and see the history of everything in perfect detail doesn't mean we can know nothing about it.

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Pint

Two worlds orbiting each other without a star.

I propose we name them Fred and Ginger

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Facepalm

Re: Two worlds orbiting each other without a star.

That's without a star, you have two there.

I suggest Ant and Dec. Nothing even remotely stellar about them.

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Thumb Up

Space 1999

Space 1999 ... a possible reality rather than just scifi

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Re: Space 1999

+1

Reading through this whole article, I was thinking of that series.

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Angel

Solar 2

Sounds like the boffins spent the week playing Solar 2 then wrote it up as a paper. Fun game if you like your physics lite.

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Bronze badge

Rogue planet "tootling" through the Universe?

I've never heard it described quite that way before. I assume that's an astronomical term?

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Anonymous Coward

Re: Rogue planet "tootling" through the Universe?

It's due to the sound it makes

in a vacuum.

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Angel

what are words worth in the face of this stunning news?

oh fabulous space sauce....

I wandered lonely as a rogue planet

that floats on high o'er space shuttles and moons

when all at once I saw a crowd,

A host, of boffins, commentards, buffoons;

Beside glowing panels, a curious frieze,

Whistling in the dark, shooting the breeze.

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