Isn't Hauméa officially part of the club, too?

It's never been that simple. When they were discovered in the early 1800, Ceres, Vesta, Pallas and Juno were listed as planets, until astronomers started to find a shitload of rocks in these parts, most of them quite small, and devised the words "asteroids" and "minor planets" ; Pluto was found in 1930 ; our perception of the "outer limit" of the solar system is steadily expanding with new stuff being added to the outer fringe...

Our knowledge of the solar system has always changed to aknowledge new discoveries. And honestly, thinking about all that is "out there", waiting to be discovered/explored, is quite exciting :)

There's actually strong mathematical evidence for a ninth planet.

For the TL;DR crowd: there's something out there synching up the orbits of the six furthest trans-Neptunian objects found so far. (It could be random chance, but the odds against that are at least 10,000:1).

The best mathematical fit appears to be a super-Earth, about 10x our mass, orbiting the sun about 20x farther out than Neptune. But it'd be so small and dim that scientists still need to narrow down where it most likely is, before they can even start to mount a serious telescopic search.

For those for whom even that was too many words, here's an infographic.

Yay! I'm on the map too. Thanks for helping me find myself!
Or it could be a cluster of asteroid-like bodies (like the Trojans, only not bound to a planet) instead of a solid planet. Only the total mass can be inferred, not that it is coherent.

Possible, but extremely unlikely. Over the course of eons, either all of those individual bodies would have aggregated together anyway, or the counter-pull from Sedna and the other larger bodies would have slowly stripped such a cluster apart, one planetoid at a time.

I just took the list of wikipedia. But did see a article stating that haumea is adwarf planet

Yeah, but in the meantime I've been working on my fr--

..On second thought: no, that's gross.

It definitely is, right in the list from the IAU over here (under "How many dwarf planets are there?"). And according to Mike Brown's long list, 2015RR245 is in category two, see it there at #20, so if this one is listed as dwarf officially, probably plenty more should be. Why did they choose to designate this one as such so fast and not the others yet, not sure.

Edit: Strike that, seems to be media mixing up terms here. The IAU recognized the discovery and the discoverers considered it a dwarf planet, but I'm not seeing any formal statement that it was actually recognized as such. It'd be odd if it was, after all.
Initial release

Intergalactic planetary, planetary intergalactic.
Another dimension, another dimension.

Mmmkay, but why a "super earth" and not just another "small" gaz giant, like Neptune or Uranus? Would sound more logical for the outer solar system, and an unusual orbit like the one hinted at in the article would explain why nobody saw it yet.

Depends where it formed and on its exact size. If it actually formed out there, expect a large icy ball more like a giant Pluto. But there doesn't seem to have ever been anywhere near enough material for that. So another option, perhaps most likely, is to have it form closer in and then have it kicked out to such a distant orbit, in which case it could be either rocky or gaseous, depending on exactly where it formed and how quickly it was kicked out. And another option is for it to be a captured planet from another passing star a long time ago, in which case it could be anything. All are pretty low probability though, with the formed close and then kicked to a wide orbit seeming most likely of the bunch but not even that too much.
So so far it's just a theory that will be hard to prove. And hard to know where to look, on such a large orbit, even if this one is true and not competing ones of multiple smaller planets, really pretty much impossible to prove with current technology, or I see a larger and closer one also suggested, but that seems very unlikely. Either way, there's a lot of space to scour for something that'd be less than 4x Earth size if an ice giant like Neptune or Uranus, less if icy world, even just 2x Earth size if rocky, and expected to reflect next to no visible light. Few, if any, current telescopes could spot it in infrared if it's in the outer parts of its orbit.

It could very well be. There's such a huge gap between the mass of Earth (the largest rocky planet) and Neptune (the smallest gaseous/icy one) that no one is quite sure what the interim possibilities might be like.

I used the term "super-Earth" because in the vastness of the Kuiper Belt, a rocky body seems more likely than a gaseous one: passing rocks can (given billions of years) eventually come close enough to merge, whereas the density of space makes gathering enough individual atoms to form a gas giant extremely unlikely at best.

But Cavalary is also correct: there's a fair likelihood that whatever's out there actually formed a lot closer to its parent star — whether that star was our own sun or another stellar body — and got kicked out or captured into its current orbit. In which case, all bets are off as to its composition.

Fun fact: Neptune used to be closer to the sun than Uranus, but it became the unfortunate victim of a resonance battle between Jupiter and Saturn; it got kicked out to its current orbit, and is actually lucky it wasn't ejected altogether. (A leading theory says that there may have been at least one other large body that wasn't so lucky, and did in fact become a rogue interstellar planet. That body is almost certainly NOT the object that scientists think they've found; if it were, it would've been orbiting the sun in the same plane as the other eight planets, not at the skew angle it appears to have.)

For a fun little example of how easy it is for orbits to change and bodies to collide or be ejected, toy around with this gravity simulator a bit.

Very interesting information. With each planet discovery we are in one step closer to solving the universe mystery . It's curious when we have the possibility to travel in a space like by plane. I like astronomy a lot.