10th planet found in our solar system

I think that the article makes a suggestion there or mentions someone's suggestion. It doesn't say that they have already named it.

They aren't comets: they are plutinos, that is they orbit like Pluto. Maybe 2003UB313 isn't one but a new type or maybe a scattered disk KBO (like Ixion) - I'm unsure. Sedna does orbit +/- like a comet but, unlike these, it knows where the plane of the ecliptic lays.

There are 3 possible reasonings to decide which objects that orbit the Sun are planets:

1. Size: if we want to be scientifical, the only natural delimiter of size is that of roundness due to self gravitational pull. In this case all object orbiting the sun of the size of Ceres or bigger are planets.
2. Population: size is only taken in account relative to other objects in the same area. That would exclude Pluto being a planet, as it's just one among many simmilar objects in the KBO (though the most brilliant one, and also was the largest one till the new discovery) but not Mercury, even if it is smaller than 2003UB313.
3. Cultural: this criterium can't be scientific and would give way to many different interpretations. Until the late 18th century there were only 6 planets, the smallest of them being Mercury, the faintest being Saturn. The addition of Uranus and Neptune wasn't any problem as they are large "normal" planets but Pluto is becoming a problem now: on one side, for 75 years it's been considered the outermost planet; on the other side it resembles the case of Ceres, that was called a planet only until other similar objects were discovered and the Asteroideal Belt was defined. So, after all, unless you are a conservative teacher that wants textbooks being "eternally" self-consistent, we have to go back to the two "scientifical" possibilities above.

My own (provisional) conclussion is that size (roundness) should be used as criterium to define planetoids, while population might be used to define planets as such. In this regard Sedna should be considered a planet until other objects of the same type are found in the same region but Pluto not anymore.

Alternatively we can use only size (roundness) as criterium and consider all the 17 known round objects as planets, though some would be minor planets, some would be medium (earth-like) planets and some would be major gas planets. In this case, Mercury would probably be a minor planet, just like Pluto or Ceres or 2003UB313.