Yesterday I watched an interesting docu about extra solar planets. One part was about so called "Planemos".....Planets that have no solar system and just wander around. Sometimes they become "trapped" in another star sytem though. The thought of wandering planets is mind boggling to me...even more so the thought of a planet just "appearing" and becoming trapped in our solar system. I wonder what effect it would have on earth if another planet of...lets say similar to earth mass....gets trapped in our system and "settles" somewhere in the habitable zone.
Planemos
- Thread starter FreddyE
- Start date
I've always preferred the term "rogue planet", which may or may not have official recognition. 
The effects of being trapped in our solar system would be a distortion of the planetary orbits. The reason our solar system behaves sanely is because of the large mass of the sun holding everything in position, combined with fairly large separation of the planets.
If a new earth sized planet passed close enough to the earth, or mars, or venus, then they would be pulled into eccentric orbits, which may set things up for a collision in the future. I don't know if the inner part of the solar system could support a new planet, and remain stable.
The effects of being trapped in our solar system would be a distortion of the planetary orbits. The reason our solar system behaves sanely is because of the large mass of the sun holding everything in position, combined with fairly large separation of the planets.
If a new earth sized planet passed close enough to the earth, or mars, or venus, then they would be pulled into eccentric orbits, which may set things up for a collision in the future. I don't know if the inner part of the solar system could support a new planet, and remain stable.
The odds of that are low. The relative velocity of any planemo passing through the Sol system would probably be too high for it to be captured. If by some striking coincidence it were moving slowly enough to be captured, it would be in a highly eccentric cometary orbit at first and would probably take tens of millions of years to settle into anything resembling a regular orbit.
I've always preferred the term "rogue planet", which may or may not have official recognition.
The difference is that a rogue planet would be a planetary body that formed within a star system and was later ejected. A planemo (planetary-mass object) is a small body that formed on its own and was never part of a planetary system; thus, it's got the mass of a planet but isn't technically a planet or former planet, because a planet is a body that orbits a star.
Not really. Smaller systems behave just as "sanely," such as the systems of moons around Jupiter and Saturn. It's just that our system has had time to settle into a stable configuration. In the early history of the Solar System, it's now believed, there were many planetary-mass objects formed, but many collided or were jettisoned from the planetary disk by the inward migration of the giant planets. Jupiter's gravity in particular is a dominant force in the arrangement of the Solar System, despite its separation from the others. Gravity has no range limit, after all.
As I said, such a change would take many megayears, if it happened at all. If Jupiter's gravity stole enough momentum from a planemo or rogue, it might settle into an inner-system orbit eventually, and while it gradually became less eccentric, that would have gradual effects on the orbits of the other inner planets. But those effects would most likely be subtle, and would be quite undetectable on the time scale of a human lifetime. We're not talking When Worlds Collide here.
And there's no reason why a merely Earth-sized planemo or rogue would have enough gravitational influence to render the whole inner system "unstable," beyond that subtle effect on the status quo as it shifts to a new equilibrium. It would probably take something on a Jovian scale to have a catastrophic effect.
As for the collision risk... the Solar System isn't a pool table. Or if it is, it's one where the "balls" are the size of bacteria. The odds of collision are negligible.
All Seeing Eye
Admiral
I've read many 'theories' if that's what you call them online which says Venus was a rogue planet and got caught in our solar system.
Is there any evidence such planets could actually be formed? I find it hard to believe a planet could be formed outside of a star system. In a star system the rocks and materiel that make up planets are abundant and are constantly circling the star allowing time for them all to clump together and form a planet but out in the dead of space I can't see it happening at all.
What if the planet was caught in the location of the asteroid belt?
Is there any evidence such planets could actually be formed? I find it hard to believe a planet could be formed outside of a star system. In a star system the rocks and materiel that make up planets are abundant and are constantly circling the star allowing time for them all to clump together and form a planet but out in the dead of space I can't see it happening at all.
What if the planet was caught in the location of the asteroid belt?
I've had a story idea on the backburner for a really long time with just such an idea, and that it's orbit isn't in the same plane as the rest of the planets so there's less of a chance of collision. However, with all the orbital mechanics involved, I'm reluctant to do it unless I can figure out how to get it somewhere near real, if you know what I mean.
All Seeing Eye
Admiral
You must be thinking of Immanuel Velikovsky's infamous book Worlds in Collision from the 1970s, a ludicrous piece of pseudoscience that attempted to explain Biblical and mythological events by postulating an inane set of astronomical catastrophes, mainly the idea that Venus was a "comet" that got jettisoned out of Jupiter somehow, careened around the system like a pinball, caused a lot of Biblical miracles (like Joshua or whoever stopping the Sun in the sky), and finally settled down where it is now. Pretty much every bit of it is contradicted by basic physical law, our knowledge of the planets, and our knowledge of history.
There's not a shred of actual science to suggest that Venus's origins are extrasolar. For one thing, it has the most circular orbit of any known planet in the Solar System, which makes it the worst possible candidate for a captured rogue (since a captured body would have a high eccentricity). A captured body would probably also have a much higher inclination than Venus does.
Where do you think that "materiel" in a star system comes from in the first place? Interstellar space is full of gas and dust. Any concentration of that material, large or small, will eventually collapse under its own gravity if it doesn't get dissipated somehow. We know this mechanism produces stars of all sizes and brown dwarfs as well; so there's no reason it couldn't happen with something even smaller. If you have something smaller than the amount of mass that forms a brown dwarf, you get a body like a Jovian planet, too small to undergo fusion and thus not qualifying as a brown dwarf. This is what scientists are generally talking about when discussing planemos -- bodies along the lines of Jupiter or Neptune. Although I see no reason why there couldn't be smaller bodies as well.
If a planet could have a stable orbit there, there wouldn't be an asteroid belt. Remember, Jupiter's gravity is the dominant force in shaping the orbits of the planets. After all, it's more than twice as massive as the other seven major planets combined. And its gravity prevents planetesimals from about 2-5 AUs from coalescing into planets. It would be the influence of Jupiter's gravity that would ultimately dictate the disposition of any rogue body that got captured by Sol, and whatever orbit it settled into would probably not be in the Main Belt.
And again, the odds of any capture event are extraodinarily low, due to the differences in velocity and momentum I mentioned before.
In fact, this is exactly how Pluto orbits the Sun. And, indeed, the comets. In these cases, not only are the orbits inclined significantly compared to the general orbital planes of the other planets, but also venture within, and in the case of some comets directly intersect, the orbits of other planets, due to their eccentric, ellipsoid, paths.
All Seeing Eye
Admiral
Nope, what I've read is that Venus got caught in our solar system before the Earth even became habitable.
Well, could you provide a link to where you read that? The only thing I can find on the subject is this page:
http://everything2.com/title/The+theory+that+Venus+came+into+our+solar+system+relatively+recently
And the original poster is clearly influenced by Velikovsky, making some of the same false statements and feeble attempts to use the theory to explain Biblical events. The subsequent posts will explain better than I can just why the idea is such complete nonsense.
There is absolutely no scientific basis to the idea that Venus came from outside the Solar System or has a young origin, and there is abundant scientific evidence to the contrary. Here's a page that refutes the "young Venus" idea:
http://www.talkorigins.org/faqs/venus-young.html
As for the idea you're describing, that Venus was "captured" billions of years ago, it's certainly not an actual scientific theory, and I can't even find a single online reference to it as a conjecture. I have no idea where you got this notion, but there's not a shred of logic or evidence to support it.
All Seeing Eye
Admiral
I aint got a clue, was years ago.
Well, it apparently doesn't exist anymore, and there's no corroboration for the idea anywhere, so you're better off forgetting it. It does not represent what any actual science tells us about Venus.
If Venus orbited in an opposite direction around the sun from other planets and had a radically angle to it's orbit around the sun then it would be a good case for that. As it stands right now.... not much of a case.
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