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> Another factor that kept ED138 hidden is that it is on the same plane as our galaxy. “For the last 20 years, the object has kind of been looping its way across the Milky Way, from our point of view,” Holman explained. “People don’t typically search for things in the Milky Way, because there’s so many stars that it’s really hard to find moving objects.” [1]

This thing was actually found despite its location, not because of it. If it had been in the opposite part of the sky we almost certainly would have spotted it sooner, given that it's one of the brightest TNOs we've discovered.

We're finding it now because Vera Rubin (the instrument that found it) just came online and is exceptionally good at finding these kinds of objects specifically, even when they're hiding amidst a dense population of stationary background stars.

[1] https://edition.cnn.com/2026/10/28/science/ed138-dwarf-plane...

Thanks!

You can also turn on the known asteroid population:

https://dahlend.github.io/ketev/#t=2026-11-12.9717&sel=2026%...

Everything runs in the browser, served as a static github pages so I don't have to think about hosting or anything.

I've built a similar app with the same sources, it works pretty well on mobile: https://spacemap.co/s/54667839/2026%20ED138?at=now,-2.48520,...

it worked for me, you can drag the sidebar to make it smaller.

but it's not great for mobile

Classifications are useful. Even the 'proper' planets we split into terrestrials, Jovian giants, and ice giants. Each planet is individually interesting in itself. One might even argue all of the bodies in the Solar System exist on a continuum of mass from the tiniest mote of space dust, to rocks and asteroids, to moons and dwarf planets to terrestrial planets, ice giants, giants, and then the Sun, and then hypergiant stars, neutron stars, black holes, and then supermassive black holes, so let's call all of them 'celestial objects'—which we kind of do. But such a catch-all is pointless. Each object behaves very differently, with wildly different physical laws governing its interior and its neighbourhood.

Classifications impose structure on a collection of celestial objects, and we can derive relationships, commonalities, understand their development, the physics governing these objects, and build useful physical and mathematical models to widen our understanding of the universe.

Most reasonable scientists understand that some of these objects will blur the edges—like many moons being more massive and larger than Mercury. Or like the largest super-Earth exoplanets being nearly as massive as Neptune, or the largest gas giant exoplanets being 30-80 times as massive as Jupiter and hence having a surface temperature of ~2000 K. But that is part of science, and possibly even where the most interesting work is.

The backlash was all just populist ignorance on display. There were multiple concrete measures of planetness constructed and Pluto is an outlier in all of them. One of these things is not like the others.

Yeah. The gas giants are clearly way different from rocky planets and we still keep them all under one taxonomical grouping. Pluto and other bodies should have been an extension of that: make them dwarf planets or whatever other classification you want. But they're still planets. Theres no "demotion" just a further categorization.

To me this subject is just a combo of bikeshedding[0] lumper and splitter[1] stuff by people who aren't domain subject experts.

I find people do this a lot with space stuff because they're interested in it but don't really know much about it.

It's ultimately irrelevant to the subject at hand and detracts from the conversation.

https://en.wikipedia.org/wiki/Law_of_triviality

https://en.wikipedia.org/wiki/Lumpers_and_splitters

Ok so we have 50 planets?

Yeah, I don't like when a modifier is mandatory. If they chose to label them "dwarf planets" then it should be expected that people will leave off the modifier "dwarf" when being concise.

If they really didn't want people to continue to refer to them as planets, then they should have chosen a completely different noun.

Eris has more mass. And our Moon, the Galilean moons of Jupiter, Titan and Triton are all both larger and more massive.

A planet is an object that:

  a) orbits a star, and is not a star nor a brown dwarf itself;
     i) a star is an object that is massive enough and hot enough to conduct protium fusion in its core
    ii) a brown dwarf is an object that is massive enough to conduct deuterium fusion, but insufficiently massive (and hence insufficiently hot) for protium fusion  
  b) has attained hydrostatic equilibrium, that is, it is spheroidal;
  c) it has cleared its local neighbourhood of 'rival planets' since its birth;

There is some controversy about when giant planets stop being giant planets and start being brown dwarfs—typically around 30 Jupiter masses—but this is an active area of research, to understand the fusion ignition in these objects. As I mentioned in another comment, classifications are useful. Of course they are arbitrary and they are biased—they were decided by humans. But the entire point of science is to push the edges of our understanding and reduce these biases and make our models more general and less arbitrary.

I agree with this picture as the barycenter argument seals it for me. The only leap left is for me to believe Ol'Jove as a failed star (it still emits heat in excess of what it derives from Sol) and we find ourselves cozily herded about by a binary star system.

You merely need to define the term "NinePizza", which is a collection of nine pizzas—and then have your very educated mother serve that. This doesn't present any problems philosophically, since we already have terms like "Solar System" for collections of disconnected objects.

Uranus and Neptune already are a two-member class (“ice giants”).

Does Saturn have enough density to count, though? I mean, from a certain point of view, it's more of a spheroid of hydrogen with a bit of helium. Maybe we need a new term for it, like "Planetary nebula"? ;)

So, a factor of 14.4 is enough to put the line between Ceres and Pluto, but a factor of 23.0 is not enough to put it between Pluto and Mercury?

Yes, those classifications are arbitrary, but then any classification is. If you want to consider Pluto as a planet, you have to include quite a lot of other bodies, which are all qualitatively and quantitatively different from the 8 (which themselves are in 2 qualitatively and quantitatively different groups. Or 3, depending on who you ask).

In the grand scheme of things, it does not matter and astronomers won’t care about the general public’s feelings. It is utterly pointless to get worked up about these things.

> The updated IAU definition is essentially reverse engineered to fit how they wanted to classify the planets.

I wholeheartedly agree with this take. I have something of a personal hatred of poorly executed retconning thus I present the following proposal.

For the sake of simplicity we should use even powers of 10 with earth as the primary reference point. Note that the earth is 10^24, mars is 10^23, and the earth's moon is 10^22 (pluto is also 10^22 and less massive than the earth's moon). It seems "obvious" then that 23-25 are planets, 22 or less are relegated to dwarfs, and 26 and over are giants (jupiter is a 27 and the sun a 30 for reference).

By that logic, if we want to consider pluto a planet then the earth's moon also has to qualify. I don't really care one way or the other but that just doesn't seem sensible to me.

Glad that artist's impression was there so I could get a good idea of what Planet 9 may or may not look like.

Why not?

Why not? Blindsight by Peter Watts got one, Big Ben.

then we need all the previous posts about it linked