This object appears to be in a very eccentric orbit (0.948), and with an H magnitude of 3.55, so it is likely hundreds of km in diameter. Ceres for reference has a H magnitude of 3.33 (smaller H is bigger diameter).
If you want to know what H means: https://en.wikipedia.org/wiki/Absolute_magnitude#Solar_Syste...
https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2017%...
Out at 90 AU, and by the year 3000 is out at 500 AU, and that's still not anywhere near maximum distance. Looked like it was going to be 10,000+ years orbits or longer, and probably out at several 1000 AU at maximum.
Little skeptical it would even orbit normally with how heavily eccentric it is, and the extreme distance at maximum. Way... out beyond the heliopause / heliosheath / termination shock.
The preprint announcing the discovery lists the semi-major axis as 838 au, so the major axis is 1676 au and aphelion is about 1630 au.
I think there is a tendency for them to have their PE out to one side and the AP out to the other giving a fairly obvious pattern indicating another larger object is shepherding the others into their orbits.
from [0]:
> Before its demotion from planet status in 2006, Pluto was considered to be the planet with the most eccentric orbit (e = 0.248). Other Trans-Neptunian objects have significant eccentricity, notably the dwarf planet Eris (0.44). Even further out, Sedna has an extremely-high eccentricity of 0.855 due to its estimated aphelion of 937 AU and perihelion of about 76 AU
> ...
> Comets have very different values of eccentricities. Periodic comets have eccentricities mostly between 0.2 and 0.7, but some of them have highly eccentric elliptical orbits with eccentricities just below 1; for example, Halley's Comet has a value of 0.967
so possibly an ignorant question, as someone who's interested in astronomy but doesn't follow it very closely - when this is categorized as a dwarf planet, does that include "it might be a comet" as a possibility? or have they already ruled it out as a possible comet through other observations?
0: https://en.wikipedia.org/wiki/Orbital_eccentricity#Examples
Back from the 1810's to the 1870's or so, most people considered Ceres, Vesta, and things like that to be planets- they were bodies that wandered around the solar system, that meant they were planets. When the numbers started to get into the 20's, everyone decided to create a new category, "asteroid" (Greek for 'star-like') and put all of the smaller things in that. So when Pluto was discovered in 1930 it was slotted right into the planet category. Pluto was discovered mostly by accident, because Clyde Tombaugh was amazing at working the blink comparator, and finding the one dot that moved in between the two pictures of the night sky a few days apart.
However, by the 1990's and 2000's you had computers and digital cameras, which are even better than Clyde at finding things that move, and quickly the number of planets started to go up- and it was clear that once we had thoroughly mapped the ~~Oort Cloud~~ (meant Kuiper Belt, see below) etc. we would have dozens of planets. And so once again astronomers decided to create a new category, just like they had with asteroids a century earlier. This time they drew the line in such a way that Ceres got moved from asteroid to dwarf planet- it has enough mass to be roughly round, so after over a century of being an asteroid it became a dwarf planet.
This is how things always work in science: we discover something, then we discover more of them, and re-categorize everything based on the new discoveries. It's just more noticeable with Pluto because reciting the planets is done by every schoolkid in a way that they don't for subatomic particles or for species of voles or whatever.
So it’s interesting that the Oort Cloud is often mentioned as a real thing. Surely there are plenty of bodies discovered which are orthogonal to its existence, but Oort’s “Cloud” itself still enjoys only the status of hypothesis and not reality.
https://en.wikipedia.org/wiki/Oort_cloud
Sadly, even Wikipedia editors seem unable to distinguish between the formal definitions of “hypothesis” vs. “theory” when delivering such a scientific article.
Is there a chance that Alpha Centauri also has its own cloud that overlaps with it?
Would AC influence the cloud and adjust the orbit of smaller comets?
Oort Clouds are mostly empty space, so there wouldn't be much direct interaction. But there would certainly be gravitational effects.
My guess (FWIW) is there's more out there than we suspect, likely including plenty of rogue/wandering planets between systems.
There’s no reason that Pluto couldn’t have remained a proper planet. It’s big enough to be round and its largest moon is big enough to be round. Mars doesn’t have any round moons. Mars is still a planet.
This doesn't sound like a science way of doing things. The definition of planet would have to be literally changed to add "Or has to have been discovered before 19XX" in order to keep Pluto without becoming an unbounded set. If you're annoyed at all the pedants correcting kids or anyone else talking about the nine planets, I'd take it up with them for uselessly debating such a fine distinction, like a chemist arguing about the word "Sodium" on a Nutrition Facts label.
I would argue the colloquial definition has indeed been changed in the above way, in that most people would say that what Mars, Venus, and Pluto have in common is they're all planets, and only a few would remember the odd factoid that the dwarf planet designation was created.
It's okay for the colloquial definition to be different than the scientific one. There isn't any use case where that will harm anyone. It's not like we're chartering flights to "All Planets" where space tourists are going to be ripped off, limited to 8 planets by the technicality and missing out.
What’s a “moon” versus a “planet”? Earth is a moon of Sol, is it not? Why is having a lot of planets a problem in the first place? Why do we have to restrict the definition at all? If 2-3 stars are at the center of a star system, are the planets in that star system planets, or something else? What if they’re small?
This whole scene is ripe for people who want to put their stamp of opinion on something to go nuts arbitrarily.
We already have the word "satellite" for "things that go around other things" right? I think "moon" is just "satellite of a planet" for convenience in discussing that subset.
> Why is having a lot of planets a problem in the first place?
I think keeping the number manageable is explicitly something we keep around to help kids grasp the main entities in the solar system. If we just said "there are 235 planets" it would be silly to try to teach them all, so we'd probably just settle for "The top 10 biggest planets" or something. Having a definition instead of a number to bound the set isn't much less arbitrary than teaching the "top 10," but since the long tail clearly starts after #8, "Top 8" would be the only guaranteed stable set to give special treatment to, which is what we've arrived at with the official definition.
No. The sun is a star, so it doesn't get to have moons. It has planets. If Jupiter started generating heat from nuclear fusion reactions, we'd call Io a planet right before we boiled to death, and with our dying breath we'd add "and also, it's no longer a moon".
Putting a leash on a cat doesn't make it a dog, and both of those creatures have four legs even if you call the tails of each a leg. A planet revolves around a star, a moon revolves around a planet (revolving around a star). There's further elements which make Ceres and Ed White's lost glove not a planet or a moon, respectively, but planets and moons are distinct and non-overlapping categories.
Planets orbit stars. Moons orbit planets. That's a clear and easy distinction. Planet vs dwarf planet isn't so clear to most.
If a super massive planet and two stars orbit each other in the center of a star system, all the planets that orbit those stars are moons then technically, right?
This is all super fuzzy and completely arbitrary. These concepts are constructs. Humans could make them better. Instead, everyone decided to make it all worse.
Satellites? Natural or manmade, small or big, doesn't matter.
At present, purely theoretical: we don’t know of any. They are probably quite rare, but we don’t really know - maybe, in centuries to come, we’ll know of dozens of examples; maybe, there are none to find in this entire galaxy
Mercury, Venus, Earth, Mars, Ceres, Pallas, Juno, Vesta, Jupiter, Saturn, Uranus, Neptune, Pluto, Eris, Makemake
(Plus some more).
Why should giant planets be in same category as normal ones? Why mixing ringed with non-ringed? Why mixing moonless with moon-enabled? Gas/liquid ones and solids? I could go on for a long time.
Current estimates expect about 200 Pluto-sized objects in the Kuiper belt and about 10'000 in the surrounding region.
Compared with 4 rocky planets, 2 gas giants and 2 ice giants.
Why remove Pluto?
The definition of a Planet could be whatever we want. It could be "these named entities are planets, other things are not planets" if we wanted. That makes a hell of a lot more sense to me than anything else, because eventually we are going to find planets which really blur the boundaries we have currently. Until we observe the entire universe, any set of rules we come up with are going to appear to be wrong in some situations.
If it were a ratio then 0 would be escape and 1 would be circular.
If not that section, apologies for missing what you're trying to point out - I'm just trying to see what needs to be cleaned up so I can make an edit if needed.
How big is that compared with other dwarf planets/ Moons? If you sort all dwarf planets by size, which position does this take (approximately)?
Pluto -> 2300 Km
Ceres -> 950 Km
Fobos(Mars) -> 25 Km
With an orbit somewhere around 28k years, it reached perihelion in about 1931, at 45 au from the Sun.
Simplistic odds would seem to imply that there's over a hundred more dwarf planets just like this but further away, so we just haven't seen them.
Assuming 500Km, is in in the top 10 by size/mass[1][2]? Top 100? Top 1000? Top 1000000?
[1] Yes I know it's not the same. Whatever criteria is easier to measure.
[2] I guess not top 10, but I have no idea about the current knowledge of the long tail. Fake Edit: I took a look at https://en.wikipedia.org/wiki/List_of_possible_dwarf_planets So between 20 and 30???
When it's in the faraway part of its orbit, it is moving very slowly, probably only tens of meters per second, but it's still close enough to the sun to eventually fall back in for another loop.
However, if something else dense enough got close enough out there, it would be easily perturbed and have its whole orbit altered, or even be ejected.
But interstellar space is pretty void of wandering solid bodies, so it keeps falling back towards the sun.
As far as we know ... we don't know how many rogue planets are out there ... mayb be as numerous as the number of stars or even greater