I think the most interesting part is at the end of the article: "Their work indicates the potential presence of an enormous planet, perhaps up to 10 times the size of Earth."
Dwarf planets are apparently somewhat plentiful in our solar system, but such a giant would really tickle the fantasy even if far from the sun.
I suspect that in the next ~30yr we'll either find planet 9 or find something else to explain the odd orbits of small things beyond Neptune. There's been a ton of progress in our understanding of that part of the solar system in the last 20yr.
For comparison it is often announced in the media that voyagers 1 and 2 have "left the solar system". Voyager 1 is about 144AU out right now. There are things in orbit of the sun with aphelions from 1500 to 3000AU.
The same folks also discovered https://en.wikipedia.org/wiki/2015_TG387 a while back, with a 1955 AU aphelion. That is a lot more far out. It's crazy to think about an orbit taking over 32 thousand years. I wonder what the sun looks like from out there.
Yeah, I remember that. There is speculation in the astronomy community that based on the sheer amount of cubic volume that is out there, the distance, the small size and dark color of Sednoids and other TNOs, and the small area that's been systematically searched so far, that there may be literally thousands of them out there and a total mass of 75% of Jupiter.
The orbit isn't well known, too short an observation arc, but a rough one has been calculated. It probably reaches somewhere between Uranus and Neptune, but not Saturn.
The first diagram, of the distances from the sun of those objects including the classical planets, it's not really a sensible thing to show.
If you look at the second diagram some of the orbits are very elliptical so the distance from the sun changes significantly. And it's also not the case that one objects it always the same "rank" from the sun.
The article mentions that the orbital elements of Farout (2018 VG18) are currently unknown. We don't know if its orbit is similar to the eccentric orbits of the other minor planets mentioned. All we know is that it is currently about 120 AU from the sun.
"2018 VG18 is much more distant and slower moving than any other observed Solar System object, so it will take a few years to fully determine its orbit."
Why does the article keep referring to it as a planet? That's highly confusing and disingenious, as in, probably trying to get the pop sci sites to start yelling about it as a planet.
The International Astronomical Union defined a planet [0] as an object that:
(a) orbits the sun, (b) has sufficient mass to be round, or nearly round, (c) is not a satellite (moon) of another object, and (d) has removed debris and small objects from the area around its orbit
The dwarf "planets" often suffer from not being round (enough), and even more from not clearing out their debris in their orbit.
The flip side is the IAU came up with a definition that only allows 8 planets in the universe and ceased to be relevant for a common sense definition of planet which existed well before they did.
There are a lot of things out there that orbit stars, and it increasingly looks like just one, or even a handful, of formal definitions are going to be inadequate, even for our own solar system. We need a detailed and extensive classification system....
Well, Farout orbits the sun, is round, is not a moon. The article is silent on item d.
I don't know what to do with the information that its diameter is 500km. I guess that makes it 1/5 of Pluto's diameter, and given that Pluto is called a dwarf planet...
I believe the mass and orbital parameters necessary to clear an orbit of debris are known pretty well known theoretically, and farout won't satisfy it. This is why astronomers can "be looking for Planet 9/X/10" without searching for debris everywhere. (Likewise, knowing the rough mass is enough to know whether a body has a hydrostatic shape; you don't have to actually resolve it's shape in your telescope.)
In more detail it's not about the shape, but mass. Planets are massive enough for gravity to overcome the internal bonds in rocks and metals, making even these materials flow into a round shape.
An asteroid could be perfectly round, but its shape is based on material strength and not just gravity.
Yes, but if we want to distinguish between say asteroids and planets, or orbital pebbles and planets, we need criteria with which to do so and those are going to be at least somewhat arbitrary.
The 'cleared it's orbit' thing is also arbitrary. Pluto is sometimes closer to the Sun than Neptune for example but does that mean they share an orbit? It's mainly to exclude Ceres, which is pretty close to spherical.
The problem is any rules that exclude Ceres and also exclude the other trans-Plutonian planetoids also end up excluding Pluto. If Pluto is a planet and this new thing, why not Eris, Haumea, Sedna, orcus, etc, etc, etc.There are many dozens of them.
We do have applicable terms - planetoid, dwarf planet, so why not use them?
What I don't like about the "cleared its orbit" criterion is that it's something you can't tell from looking at the object itself. If a planet is ejected from its orbit, it becomes a ... well, we don't even have a name for what it would be. (This problem exists for "moon" to a certain extent, but a moon that's thrown out of planetary orbit would become a planet if it was big enough and an asteroid if it wasn't). It's also hard to apply: a lot of extrasolar planets we're discovering will have to be reclassified once we get better at finding smaller bodies, just like in this solar system.
> What I don't like about the "cleared its orbit" criterion is that it's something you can't tell from looking at the object itself.
Dwarf planet is a helpful term in some contexts but not others. The solar system is a dynamic system, when talking about the whole thing or its evolution it's useful to distinguish between planets and dwarfs.
Casually speaking, it's a planet - a big roundish thing orbiting the Sun. But when talking about the solar system it can be useful to distinguish between planets and dwarfs in some contexts. The 8 planets grew massive enough to 'boss' their orbits whereas the dwarf planets did not. There may be hundreds of dwarf planets hiding in the outer reaches of the solar system.
It's about 1/5 the diameter of Pluto (500km to Pluto's 2400), so quite small and definitely not a planet. It's interesting because it could give evidence about the hypothetical ninth true planet-sized object that people have been hypothesizing for awhile.
