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Hunt For Ninth Planet Reveals Distant Solar System Objects (carnegiescience.edu)
schwit1 writes: Astronomers have discovered several new objects orbiting the Sun at extremely great distances beyond the orbit of Neptune. The most interesting new discovery is 2014 FE72: "2014 FE72 is the first distant Oort Cloud object found with an orbit entirely beyond Neptune," reports Carnegie Institution for Science. "It has an orbit that takes the object so far away from the Sun (some 3000 times farther than Earth) that it is likely being influenced by forces of gravity from beyond our Solar System such as other stars and the galactic tide. It is the first object observed at such a large distance." This research is being done as part of an effort to discover a very large planet, possibly as much as 15 times the mass of Earth, that the scientists have proposed that exists out there.
A sednoid (2014 FE72) with an orbit out to 3000 AU (0,05 light years)? Talk about extreme, I would have been happy just for a couple more "ordinary" sednoids! But that's exactly the sort of thing you want to see if you're of the view that trying to group the universe into a neat collection of "stars" with "planets" orbiting them is oversimplistic. This lends credence to the notion that you're going to get shared debris between different stars, rogue planets that don't orbit stars, etc. Because with large bodies reaching that far out, it becomes pretty easy to perturb them to leave the solar system altogether.
I have no clue what the discovery of 2013 FT28 is going to say about the possibility of an additional large planet in our solar system, but I look forward to the papers on it! Hopefully it won't rule one out, and will instead better constrain an orbit
"99 dead duelists of Dios on the wall. 99 dead duelists of Dios! Take one's ring, pass it around..."
Looking at their graph (since I don't see the perihelion stated anywhere), it looks to be about 60 AU (about double that of Neptune). That's some tremendous temperature changes on that body! The equilibrium temperatures are:
((1368 / D^2 - 3.127e-6) / 4 / 5.670e-8 ) ^ 0.25 ... where D is the distance in AU. So at perihelion it'd be about 36K, but at aphelion only about 5K.
Now, this particular body is probably too small to retain significant hydrogen or helium, but you could imagine what it would be like for a large planetary one in such an orbit. It'd transition between being a hydrogen-ice planet with a helium mantle and water ice/rock core; and an ice giant like Uranus and Neptune. In its solid phase, its hydrogen-ice surface would be resurfaced entirely with every cycle and thus might be expected to be perfectly smooth, except because of the heat involved in the settling processes - and how low viscosity and structural integrity in general hydrogen ice has - I'd be willing to wager that you'd get helium volcanism and maybe even plate tectonics.
It gets even weirder if a planet at such distances as this one's aphelion were to have a moon that loses helium vapour to its planet (perhaps, for example, on an eccentric orbit getting it back at each perihelion as the planet inflates, to repeat the cycle at the next aphelion). After all, even below the boiling point, there's always some vapour pressure for helium. If you're taking that vapour away, then you're looking at evaporative cooling, and you really don't need to lose it that fast to cool to below the cosmic microwave background (because radiative exchange is so slow at those temperatures) and thus to helium's lambda point. Now you have a body with superfluid helium on it, and all of the crazy weirdness that superfluids do.
Back to our solar system - aka, a small body like 2014 FE72 - you're not going to have much hydrogen or helium. But even still, that crust is going to be going through some crazy thermal stresses at the very least. Also, neon - while not as common as hydrogen and helium, but should be more common in the outer reaches of our solar system than the inner - would pass through all three phases (melting point 24K, boiling point 27K at 1 bar; lower at reduced pressures). I wonder what sort of minerology neon would form? "Neonothermal" crystal veins, analogous to crystals in hydrothermal systems on Earth? :)
"99 dead duelists of Dios on the wall. 99 dead duelists of Dios! Take one's ring, pass it around..."
and we never get anything better than fusion drives (and Bussard ramjets don't work), then maybe a high density of these "rogue" worlds will allow the (very slow) colonization of the galaxy.
If there are roughly 1000x as many these large planetary bodies floating in interstellar space as there are stars, then perhaps it'll be feasible to travel to them in tens of years traveling at speeds achievable by nuclear fusion (hundredths of "C"). Then, using the resources there, colonies could be set up. Eventually, these will sprout new colonies, further pushing the boundaries of inhabited space until finally they reach a star.
This scheme of colonization would be unlike anything the western world, even in the days of years long voyages via sailing ships, has known. Perhaps the closest would be the voyages of the far flung polynesians who managed to spread across the vastness of the pacific ocean over a period measured in centuries(?). If any of them made it to South America (some say they did), it would be like these future voyagers making it to the next star.
Of course, we all hope for a Star Trek/Star Wars future with warp/hyperdrive bringing the stars within an afternoon's jaunt. Failing that I guess the runner up desirable future would be the hyper broadband interstellar communications network in which our downloaded selves could be digitally transferred at the speed of light to the next instancing hub (such as in Greg Egan stories of the post-singularity future).
However if neither of those pan out and if we don't learn how to make/harness anti-matter, micro-blackholes, zero-point energy, giant laser driven solar sails or ??? then perhaps this is our most optimistic future.
Maybe with immortality and suspended animation it won't be too bad. Slow trips around the galaxy indeed
This lends credence to the notion that you're going to get shared debris between different stars, rogue planets that don't orbit stars, etc.
But how many? I don't think the process of exchange can be fast - if those bodies had galactic escape velocity, after all, they wouldn't stay here for long. So they must be comparatively slow. But the distances are still large (tens of thousands of AUs) and the volume in which they could be present is really big. Would a frequent exchange mean that most of this mass (or mess?) is actually in the interstellar space? And not in some neat belts close around stars?
Ezekiel 23:20
They don't have escape velocity; they're stuck with us until something perturbs them. But the key point is that when something is that far out, it's very easy to perturb. And our stellar neighborhood is not static. Indeed, one of the alternative theories to explain the sednoids is that rather than a planet X, the orbits are due to one or more stellar passes nearby our solar system.
So far we're still not seeing very far out, we're just barely spotting these things, and only when they're near perihelion. There's much more out there yet to discover, and so far all signs point to that our solar system doesn't just "stop" anywhere, it just keeps on going. Heck, we only know about the Oort cloud because comets have such distant aphelions.
"99 dead duelists of Dios on the wall. 99 dead duelists of Dios! Take one's ring, pass it around..."
You mean 10th. You forgot about Ceres.
Under no reasonable standard is Pluto 9th. 10th, fine. I'd go out on a limb and argue at least 17th, also adding in the "planetary moons" that meet a hydrostatic definition even better than Pluto: Luna, Ganymede, Callisto, Europa, Io, Titan, and Triton. Using "planet" on the basis of of "body large enough to assume hydrostatic equilibrium but not undergo fusion" and moon as "body that orbits a planet".
Hydrostatic equilibrium is a very meaningful definition. A body not in hydrostatic equilibrium is made of primitive materials; it's the sort of place you'd go to learn about the formation of our solar system. A body in hydrostatic equilibrium has experienced internal heating, movement of fluids, chemical reactions, etc. It's the sort of place you go to learn about geology and search for life.
Or if you'd rather, you can apply the Captain Kirk test. Put it up alone by itself on a viewscreen. Would Captain Kirk say "Beam me down to that planet" or "Beam me down to that asteroid?" It's silly, but it's basically another way to say, "is the word functioning as normal people would use the word?" Of course, if there was another, bigger body in the background, they might say "beam me down to that moon". But we've all seen sci-fi where we're told that a body is a moon but people keep accidentally referring to it as a planet. The Forest Moon of Endor, for example. If it's a gigantic round thing, a part of us wants to call it a planet, even if we also know it's a moon. No reason not to just have them both as descriptive terms: a "planetary moon".
(And IMHO, if there's anything we should be kicking out of the "planet" club, it should be the gas giants... followed next by the ice giants. Seriously, how much is Jupiter like Mars?)
As for Stern, he once presented a rather interesting classification scheme (ironically, in the same paper as the Stern-Levison parameter was proposed). Basically, forget about all of these nouns, just have a good list of adjectives. You can have various things from sub-dwarf planet to super-giant planet to indicate the mass; prefixes like "gas" or "ice" or "rocky" to indicate the character: other adjectives to indicate its orbital parameters (including its "neighborhood" if you prefer), etc. Why limit yourself? Cite as many adjectives to describe it as are appropriate to the situation.
"99 dead duelists of Dios on the wall. 99 dead duelists of Dios! Take one's ring, pass it around..."