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.

Comments

Re:Wow, and I thought the existing Sednoids were n

[Rei]

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? :)

Re:There is a 9th planet

[Rei]

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.