Dwarf planet discovery hints at hidden world orbiting solar system
news.nationalgeographic.com
news.nationalgeographic.com
http://www.nature.com/news/dwarf-planet-stretches-solar-syst...
“It goes to show that there’s something we don’t know about our Solar System, and it’s something important,” says co-discoverer Chad Trujillo, an astronomer at Gemini Observatory in Hilo, Hawaii. “We’re starting to get a taste of what’s out beyond what we consider the edge.”
The journal article reports on what they know for a fact. Another planet on an unusual orbit is speculation for now, so I'm not surprised they didn't mention it - although I hope that as they gather more data they'll be able to infer its location and see it block stars or somesuch, if it exists.
http://www.newscientist.com/article/dn16501-elliptical-orbit...
Also it could be a brown dwarf which are hard to detect but will be inline with typical binary star systems observed elsewhere. It is hardly unlikely that our own sun is an exception to the rule.
Not to mention, the 'nemesis' theory is speculated by some main-stream astronomers.