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2 Planets Can Share the Same Orbit, In 3 Different Ways
StartsWithABang writes: One of the most important characteristics of a planet, at least according to the IAU definition, is that it clear its orbit of all other bodies. But if we allowed for a special caveat — the possibility of two similarly-sized objects sharing the same orbit — could we have a stable configuration where that occurred? Surprisingly, not only is the answer yes, but there are three ways to do it: to have one at the L4/L5 Lagrange point of the other, to have a close-orbiting binary planet, or to have orbit-swapping worlds, where they periodically change spots with one another. Unbelievably, our Solar System has a history of all three!
One Orbit
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Given that the third mass needs to be negligible for the Lagrange points to work (at least according to Wikipedia), to me it seems like this situation might be more like a strange type moon rather than a planet. What is or isn't a "planet" is just a random definition so there isn't really a right answer.
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How many different ways are there to rehash shit that everybody knew since forever into crappy clickbait articles?
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
Stack overflow.
Slashdot, fix the reply notifications... You won't get away with it...
This is an article for "Memento" like people.
Slashdot, fix the reply notifications... You won't get away with it...
This. Seriously, I'm getting sick of having Ethan's blog everywhere I go. Guy's good at manipulating social media, but there's nothing on any of his post that isn't just a rehash of things that Slashdot and other tech/science blogs have already linked to years ago.
One of the most important characteristics of a planet...
There's three characteristics, and this is probably the least important. But if you consider all three to be "the most" important, then I suppose it's one of them. That seems like a pretty silly way to express yourself, though. Personally, I'd probably just say "one characteristic".
Also note that we're talking about the IAU definition, which is not necessarily the only definition. Dictionaries still haven't accepted the IAU definition, and may never do so, because the IAU defines a planet as orbiting the sun, while science fiction writers continue merrily talking about planets around other stars, and show no signs of changing.
... please at least check whether the links in the submission are going anywhere...
Speak for yourself. I read the whole article, and enjoyed it. Not everyone knows all the intricate details of planetary orbits.
And don't forget that Pluto crosses Neptunes orbit as well.
Can we please have warnings on links to Forbes? Those interruptions for their (usually stupid) "thought of the day" are really annoying. Perhaps editors should look for alternative sources where possible.
const int one = 65536; (Silvermoon, Texture.cs)
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They'll say, "oh, it's okay, there's enough of a size difference between those bodies that they don't count". But the thing is that there's no way that most of the current "8 planets" would have cleared their orbits without help from the giants. It's pretty much accepted science in astronomy that Jupiter, and to a lesser extent Saturn, scattered most of the bodies in our solar system. Mars has a Stern-Levison parameter (rating of the ability of a body to scatter small bodies) two orders of magnitude less than Neptune, and Neptune has multiple Pluto-scale bodies in its orbit. Pluto may be small compared to Neptune, but it's not so small in comparison to Mars, yet Mars has two orders magnitude less ability to scatter them. Mars didn't scatter these things away - Jupiter did. Heck, a number of the models show that the planets didn't even form in their current locations.
There's all this misuse of the Stern-Levison parameter out there to say things that it doesn't. The parameter is based around a probabilistic simulation of the body and a bunch of "small bodies" with a mass distribution and orbital distribution similar to our asteroid belt. But of course, that tells you very little - our asteroid belt only has the size and mass distribution that it does today because of the influence of other planets - and when I say "other planets", I really mean overwhelmingly Jupiter (only a tiny fraction of asteroids are in Mars resonances). Jupiter has stopped these bodies from coalescing into larger bodies and scattered the vast majority of its mass elsewhere. That's not the situation that the solar system was in during formation. There were numerous large "planetissimals" scattered around. The Stern-Levison parameter says absolutely nothing about the ability of a body to scatter large planetissimals. And even concerning scattering asteroids, it doesn't state that the scatters are enough to "clear the orbit", only that their angle changes on a pass by more than a given number of degrees.
Basic point: a standard based around the "8 planets" having cleared their orbit is a lie. The science says that most of them aren't responsible for clearing their own orbits.
And while we're at it: what sort of stupid standard puts Mars and Jupiter in the same group but in a different group than Pluto and Ceres? There was a perfectly reasonable standard under discussion at the IAU conference shortly before they switched what they were voting on: a definition built around hydrostatic equlibrium. A lot of the planetary scientists left thinking that this was the version that was going to be voted on, and being happy with either "no definition" or an "equilibrium definition", saw no need to stick around for the final vote. Hydrostatic equilibrium actually is valid science, and it's very meaningful. A body not in hydrostatic equilibrium is generally made of primordial minerals. It's the sort of place you'd go to research, for example, properties of how the solar system formed. A body in hydrostatic equilibrium has undergone mass conversion of its primordial minerals to new forms. It's undergone massive releases of energy (which may still be present, depending), associated action of fluids, etc, and are the sorts of places you would go to study mineralization processes, internal processes or search for life. They're very different bodies, and there's a very simple dividing line - one that's much easier to calculate/measure than a pseudoscience "cleared the neighborhood" standard.
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On such a timeless flight.
Slashdot supports <b> and <i> tags. I don't know what kind of primordial ooze you just crawled out of, but this is civilization, son, and you'd better act like you're part of it while you're here.
There's a lot of good stuff in your post. In other star systems, there are almost certain to be Earth-sized bodies that don't have giant planets to clear their orbits. They wouldn't be classified as planets under this definition, no matter how Earth-like they otherwise are.
I agree that hydrostatic equilibrium is a better basis for the definition. I'd also propose that a system of two bodies in hydrostatic equilibrium that orbit a star, with a barycenter outside of either body, be classified as a double planet. The Pluto-Charon system is an example where Charon is massive enough relative to Pluto that the center of mass of the two bodies lies outside both Pluto and Charon.
And ends with me leaving Slashdot for a few months.
Enough of this SWAB crap!
Exactly on other side of Sun so you would never see it. But I dont think this is stable. Also since Earths orbit is ellipitical, the speed is not uniform through ot the year. So part of the years wouldnt be halfway apart and possibly visible.
No, that's pretty much always been the way it was.
It's easier to be a result of the past, but more fun to be a cause of the future! http://www.spacefinancegroup.com/
One complication - hydrostatic equilibrium also is somewhat dependent on local conditions, i.e. composition of the body. A hypothetical planet made entirely of Mercury, for instance, might be/have been in HE when only 5 feet in diameter (before it froze solid, or orbiting close enough to a heat source to remain liquid). That's of course an absurd extreme, so there's probably an example somewhere out there in the universe! :)
So IMHO, HE is a necessary criterion, but may not be sufficient. I read an article a few months ago that asserted another criterion to go with HE but I don't recall what it was. In any case, I generally agree with what you say, for what it's worth.
It's easier to be a result of the past, but more fun to be a cause of the future! http://www.spacefinancegroup.com/
My interpretation has been that the French helped with the Revolution to keep a large fraction of British forces occupied 'over there', so the French wouldn't have to fight them at home.
Also, it's a little-recognized point, but it's quite arguable that George Washington, as a fairly new officer in the British Army, accidentally started what we call the French and Indian war. He was tasked with building a fort at the confluence of the Allegheny and Monongehela rivers, which join to become the Ohio, in what is now Pittsburgh. A French force wandered by, on the way toward (IIRC) Virgina. Washington's force attacked and killed most of them (again, IIRC). As it turned out this was not, as Washington had thought, a raiding party but a diplomatic one. Oops.
But the Revolution was in fact more significant than what you propose, for at least two reasons. 1) This was the first country where Rousseau's and Locke's ideas about the sovereignty of the individual 'man' over the government were explicitly defined in the fundamental law of the nation - Britain had gone some way in that direction, but primarily only with respect to the relations between the King and the aristocracy. Even Hamilton was aghast at the prospect of the great unwashed masses actually being able to vote. 2) This was the first country that was defined not by ethnicity or geography but by the founding principle.
As various people said at the time, democracy has generally not been successful - at that time no democracy had ever survived more than about 200 years, as the two forces of people voting themselves largesse out of the public till, and the influential continually manipulating the system and the people to give themselves absolute power (sometimes using 'bread and circuses' - a term going back to Pericles, who caused the eventual destruction of Athens a few decades later) will eventually bankrupt the nation, which will then turn to military rule or defeat by a nearby enemy. From Greece and Rome to Argentina and Venezuela, we see this happen over and over again.
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They'll say, "oh, it's okay, there's enough of a size difference between those bodies that they don't count".
No, they'll just point out that while the orbits of the two planets appear to cross when looking at a 2D top-down view of the solar system, in 3D space they come nowhere near each other. The closest point in their orbits is 2 AU apart. Unless you want to say that Neptune's orbital zone its supposed to be clearing is twice the distance between the Earth and the Sun, Pluto is irrelevant.
For someone who seems to care a lot about Pluto you seem to have forgotten how absurdly tilted its orbit is.
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Since the moon orbit the sun, not the Earth, doesn't the definition of a planet not apply to the Earth ? ...
(the moon always curves toward the sun, never away, during it's 1 year journey. It does wobble on a montly basis
that allows the earh and it to swap arouind as being furthest from the sun.)
Yes, the Earth-Moon system is double planets sharing an orbit. But that doesn't mean they can't be planets. It's the common definition of the Moon that is wrong.
The Ringworld is unstable!!!
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And while we're at it: what sort of stupid standard puts Mars and Jupiter in the same group but in a different group than Pluto and Ceres?
One that looks at this picture of orbits, notices the striking difference, realizes that this clearly puts Pluto and Ceres in a completely different class of objects, with completely different origins etc, and feels like acknowledging that obvious fact?
There was a perfectly reasonable standard under discussion at the IAU conference shortly before they switched what they were voting on: a definition built around hydrostatic equilibrium(sp).
Hydrostatic equilibrium is in fact used by the IAU to designate the difference between "dwarf planets" and "small Solar System bodies". If that were made the baseline for proper planets, we'd have to add somewhere between 53 and 200 new planets. You are talking about changing our list of planets by 2500%, rather than by 13%. Not only would that not be "reasonable", that is in fact the opposite of "reasonable".
Now you could make an argument that this definition doesn't get at what truly separates the TNO's like Pluto from planets (which for me probably has to do with being made from the same primordial rotating disk of leftover Sun stuff). So yeah, it should probably be tweaked, and will have to be at some point. But until we have a better handle on how planet formation in other solar systems works, this definition is probably good enough to be getting on with.